/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.app;

import android.animation.Animator;
import android.animation.AnimatorInflater;
import android.animation.AnimatorListenerAdapter;
import android.animation.AnimatorSet;
import android.animation.PropertyValuesHolder;
import android.animation.ValueAnimator;
import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.res.Configuration;
import android.content.res.Resources.NotFoundException;
import android.content.res.TypedArray;
import android.os.Build;
import android.os.Bundle;
import android.os.Debug;
import android.os.Looper;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.ArraySet;
import android.util.AttributeSet;
import android.util.DebugUtils;
import android.util.Log;
import android.util.LogWriter;
import android.util.Pair;
import android.util.SparseArray;
import android.util.SuperNotCalledException;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import com.android.internal.util.FastPrintWriter;

import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

Interface for interacting with Fragment objects inside of an Activity 

Developer Guides
For more information about using fragments, read the
Fragments developer guide.
 While the FragmentManager API was introduced in VERSION_CODES.HONEYCOMB, a version of the API at is also available for use on older platforms through FragmentActivity. See the blog post 
Fragments For All for more details.
Deprecated:
Use the Support Library FragmentManager for consistent behavior across all devices and access to Lifecycle./**
 * Interface for interacting with {@link Fragment} objects inside of an
 * {@link Activity}
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about using fragments, read the
 * <a href="{@docRoot}guide/components/fragments.html">Fragments</a> developer guide.</p>
 * </div>
 *
 * While the FragmentManager API was introduced in
 * {@link android.os.Build.VERSION_CODES#HONEYCOMB}, a version of the API
 * at is also available for use on older platforms through
 * {@link android.support.v4.app.FragmentActivity}.  See the blog post
 * <a href="http://android-developers.blogspot.com/2011/03/fragments-for-all.html">
 * Fragments For All</a> for more details.
 *
 * @deprecated Use the <a href="{@docRoot}tools/extras/support-library.html">Support Library</a>
 *      {@link android.support.v4.app.FragmentManager} for consistent behavior across all devices
 *      and access to <a href="{@docRoot}topic/libraries/architecture/lifecycle.html">Lifecycle</a>.
 */
@Deprecated
public abstract class FragmentManager {
    
Representation of an entry on the fragment back stack, as created with 
FragmentTransaction.addToBackStack(). Entries can later be retrieved with 
FragmentManager.getBackStackEntryAt(). 
Note that you should never hold on to a BackStackEntry object; the identifier as returned by getId is the only thing that will be persisted across activity instances. 
Deprecated:
Use the 
     Support Library BackStackEntry/**
     * Representation of an entry on the fragment back stack, as created
     * with {@link FragmentTransaction#addToBackStack(String)
     * FragmentTransaction.addToBackStack()}.  Entries can later be
     * retrieved with {@link FragmentManager#getBackStackEntryAt(int)
     * FragmentManager.getBackStackEntryAt()}.
     *
     * <p>Note that you should never hold on to a BackStackEntry object;
     * the identifier as returned by {@link #getId} is the only thing that
     * will be persisted across activity instances.
     *
     * @deprecated Use the <a href="{@docRoot}tools/extras/support-library.html">
     *      Support Library</a> {@link android.support.v4.app.FragmentManager.BackStackEntry}
     */
    @Deprecated
    public interface BackStackEntry {
        
Return the unique identifier for the entry.  This is the only
representation of the entry that will persist across activity
instances.
/**
         * Return the unique identifier for the entry.  This is the only
         * representation of the entry that will persist across activity
         * instances.
         */
        public int getId();

        
Get the name that was supplied to 
FragmentTransaction.addToBackStack(String) when creating this entry. /**
         * Get the name that was supplied to
         * {@link FragmentTransaction#addToBackStack(String)
         * FragmentTransaction.addToBackStack(String)} when creating this entry.
         */
        public String getName();

        
Return the full bread crumb title resource identifier for the entry,
or 0 if it does not have one.
/**
         * Return the full bread crumb title resource identifier for the entry,
         * or 0 if it does not have one.
         */
        public int getBreadCrumbTitleRes();

        
Return the short bread crumb title resource identifier for the entry,
or 0 if it does not have one.
/**
         * Return the short bread crumb title resource identifier for the entry,
         * or 0 if it does not have one.
         */
        public int getBreadCrumbShortTitleRes();

        
Return the full bread crumb title for the entry, or null if it
does not have one.
/**
         * Return the full bread crumb title for the entry, or null if it
         * does not have one.
         */
        public CharSequence getBreadCrumbTitle();

        
Return the short bread crumb title for the entry, or null if it
does not have one.
/**
         * Return the short bread crumb title for the entry, or null if it
         * does not have one.
         */
        public CharSequence getBreadCrumbShortTitle();
    }

    
Interface to watch for changes to the back stack.
Deprecated:
Use the 
     Support Library OnBackStackChangedListener/**
     * Interface to watch for changes to the back stack.
     *
     * @deprecated Use the <a href="{@docRoot}tools/extras/support-library.html">
     *      Support Library</a>
     *      {@link android.support.v4.app.FragmentManager.OnBackStackChangedListener}
     */
    @Deprecated
    public interface OnBackStackChangedListener {
        
Called whenever the contents of the back stack change.
/**
         * Called whenever the contents of the back stack change.
         */
        public void onBackStackChanged();
    }

    
Start a series of edit operations on the Fragments associated with
this FragmentManager.
Note: A fragment transaction can only be created/committed prior to an activity saving its state. If you try to commit a transaction after Activity.onSaveInstanceState() (and prior to a following Activity.onStart or Activity.onResume(), you will get an error. This is because the framework takes care of saving your current fragments in the state, and if changes are made after the state is saved then they will be lost.
/**
     * Start a series of edit operations on the Fragments associated with
     * this FragmentManager.
     * 
     * <p>Note: A fragment transaction can only be created/committed prior
     * to an activity saving its state.  If you try to commit a transaction
     * after {@link Activity#onSaveInstanceState Activity.onSaveInstanceState()}
     * (and prior to a following {@link Activity#onStart Activity.onStart}
     * or {@link Activity#onResume Activity.onResume()}, you will get an error.
     * This is because the framework takes care of saving your current fragments
     * in the state, and if changes are made after the state is saved then they
     * will be lost.</p>
     */
    public abstract FragmentTransaction beginTransaction();

    
@hide
-- remove once prebuilts are in./** @hide -- remove once prebuilts are in. */
    @Deprecated
    public FragmentTransaction openTransaction() {
        return beginTransaction();
    }
    
    
After a FragmentTransaction is committed with FragmentTransaction.commit(), it is scheduled to be executed asynchronously on the process's main thread. If you want to immediately executing any such pending operations, you can call this function (only from the main thread) to do so. Note that all callbacks and other related behavior will be done from within this call, so be careful about where this is called from. 
 This also forces the start of any postponed Transactions where Fragment.postponeEnterTransition() has been called. 
Returns:
Returns true if there were any pending transactions to be
executed./**
     * After a {@link FragmentTransaction} is committed with
     * {@link FragmentTransaction#commit FragmentTransaction.commit()}, it
     * is scheduled to be executed asynchronously on the process's main thread.
     * If you want to immediately executing any such pending operations, you
     * can call this function (only from the main thread) to do so.  Note that
     * all callbacks and other related behavior will be done from within this
     * call, so be careful about where this is called from.
     * <p>
     * This also forces the start of any postponed Transactions where
     * {@link Fragment#postponeEnterTransition()} has been called.
     *
     * @return Returns true if there were any pending transactions to be
     * executed.
     */
    public abstract boolean executePendingTransactions();

    
Finds a fragment that was identified by the given id either when inflated
from XML or as the container ID when added in a transaction.  This first
searches through fragments that are currently added to the manager's
activity; if no such fragment is found, then all fragments currently
on the back stack associated with this ID are searched.
Returns:
The fragment if found or null otherwise./**
     * Finds a fragment that was identified by the given id either when inflated
     * from XML or as the container ID when added in a transaction.  This first
     * searches through fragments that are currently added to the manager's
     * activity; if no such fragment is found, then all fragments currently
     * on the back stack associated with this ID are searched.
     * @return The fragment if found or null otherwise.
     */
    public abstract Fragment findFragmentById(int id);

    
Finds a fragment that was identified by the given tag either when inflated
from XML or as supplied when added in a transaction.  This first
searches through fragments that are currently added to the manager's
activity; if no such fragment is found, then all fragments currently
on the back stack are searched.
Returns:
The fragment if found or null otherwise./**
     * Finds a fragment that was identified by the given tag either when inflated
     * from XML or as supplied when added in a transaction.  This first
     * searches through fragments that are currently added to the manager's
     * activity; if no such fragment is found, then all fragments currently
     * on the back stack are searched.
     * @return The fragment if found or null otherwise.
     */
    public abstract Fragment findFragmentByTag(String tag);

    
Flag for popBackStack(String, int) and popBackStack(int, int): If set, and the name or ID of a back stack entry has been supplied, then all matching entries will be consumed until one that doesn't match is found or the bottom of the stack is reached. Otherwise, all entries up to but not including that entry will be removed. /**
     * Flag for {@link #popBackStack(String, int)}
     * and {@link #popBackStack(int, int)}: If set, and the name or ID of
     * a back stack entry has been supplied, then all matching entries will
     * be consumed until one that doesn't match is found or the bottom of
     * the stack is reached.  Otherwise, all entries up to but not including that entry
     * will be removed.
     */
    public static final int POP_BACK_STACK_INCLUSIVE = 1<<0;

    
Pop the top state off the back stack.  This function is asynchronous -- it
enqueues the request to pop, but the action will not be performed until the
application returns to its event loop.
/**
     * Pop the top state off the back stack.  This function is asynchronous -- it
     * enqueues the request to pop, but the action will not be performed until the
     * application returns to its event loop.
     */
    public abstract void popBackStack();

    
Like popBackStack(), but performs the operation immediately inside of the call. This is like calling executePendingTransactions() afterwards without forcing the start of postponed Transactions. 
Returns:
Returns true if there was something popped, else false./**
     * Like {@link #popBackStack()}, but performs the operation immediately
     * inside of the call.  This is like calling {@link #executePendingTransactions()}
     * afterwards without forcing the start of postponed Transactions.
     * @return Returns true if there was something popped, else false.
     */
    public abstract boolean popBackStackImmediate();

    
Pop the last fragment transition from the manager's fragment
back stack.  If there is nothing to pop, false is returned.
This function is asynchronous -- it enqueues the
request to pop, but the action will not be performed until the application
returns to its event loop.
Params:
name – If non-null, this is the name of a previous back state to look for; if found, all states up to that state will be popped. The POP_BACK_STACK_INCLUSIVE flag can be used to control whether the named state itself is popped. If null, only the top state is popped.
flags – Either 0 or POP_BACK_STACK_INCLUSIVE./**
     * Pop the last fragment transition from the manager's fragment
     * back stack.  If there is nothing to pop, false is returned.
     * This function is asynchronous -- it enqueues the
     * request to pop, but the action will not be performed until the application
     * returns to its event loop.
     * 
     * @param name If non-null, this is the name of a previous back state
     * to look for; if found, all states up to that state will be popped.  The
     * {@link #POP_BACK_STACK_INCLUSIVE} flag can be used to control whether
     * the named state itself is popped. If null, only the top state is popped.
     * @param flags Either 0 or {@link #POP_BACK_STACK_INCLUSIVE}.
     */
    public abstract void popBackStack(String name, int flags);

    
Like popBackStack(String, int), but performs the operation immediately inside of the call. This is like calling executePendingTransactions() afterwards without forcing the start of postponed Transactions. 
Returns:
Returns true if there was something popped, else false./**
     * Like {@link #popBackStack(String, int)}, but performs the operation immediately
     * inside of the call.  This is like calling {@link #executePendingTransactions()}
     * afterwards without forcing the start of postponed Transactions.
     * @return Returns true if there was something popped, else false.
     */
    public abstract boolean popBackStackImmediate(String name, int flags);

    
Pop all back stack states up to the one with the given identifier.
This function is asynchronous -- it enqueues the
request to pop, but the action will not be performed until the application
returns to its event loop.
Params:
id – Identifier of the stated to be popped. If no identifier exists, false is returned. The identifier is the number returned by FragmentTransaction.commit(). The POP_BACK_STACK_INCLUSIVE flag can be used to control whether the named state itself is popped.
flags – Either 0 or POP_BACK_STACK_INCLUSIVE./**
     * Pop all back stack states up to the one with the given identifier.
     * This function is asynchronous -- it enqueues the
     * request to pop, but the action will not be performed until the application
     * returns to its event loop.
     * 
     * @param id Identifier of the stated to be popped. If no identifier exists,
     * false is returned.
     * The identifier is the number returned by
     * {@link FragmentTransaction#commit() FragmentTransaction.commit()}.  The
     * {@link #POP_BACK_STACK_INCLUSIVE} flag can be used to control whether
     * the named state itself is popped.
     * @param flags Either 0 or {@link #POP_BACK_STACK_INCLUSIVE}.
     */
    public abstract void popBackStack(int id, int flags);

    
Like popBackStack(int, int), but performs the operation immediately inside of the call. This is like calling executePendingTransactions() afterwards without forcing the start of postponed Transactions. 
Returns:
Returns true if there was something popped, else false./**
     * Like {@link #popBackStack(int, int)}, but performs the operation immediately
     * inside of the call.  This is like calling {@link #executePendingTransactions()}
     * afterwards without forcing the start of postponed Transactions.
     * @return Returns true if there was something popped, else false.
     */
    public abstract boolean popBackStackImmediate(int id, int flags);

    
Return the number of entries currently in the back stack.
/**
     * Return the number of entries currently in the back stack.
     */
    public abstract int getBackStackEntryCount();

    
Return the BackStackEntry at index index in the back stack;
where the item on the bottom of the stack has index 0.
/**
     * Return the BackStackEntry at index <var>index</var> in the back stack;
     * where the item on the bottom of the stack has index 0.
     */
    public abstract BackStackEntry getBackStackEntryAt(int index);

    
Add a new listener for changes to the fragment back stack.
/**
     * Add a new listener for changes to the fragment back stack.
     */
    public abstract void addOnBackStackChangedListener(OnBackStackChangedListener listener);

    
Remove a listener that was previously added with addOnBackStackChangedListener(OnBackStackChangedListener). /**
     * Remove a listener that was previously added with
     * {@link #addOnBackStackChangedListener(OnBackStackChangedListener)}.
     */
    public abstract void removeOnBackStackChangedListener(OnBackStackChangedListener listener);

    
Put a reference to a fragment in a Bundle. This Bundle can be persisted as saved state, and when later restoring getFragment(Bundle, String) will return the current instance of the same fragment. 
Params:
bundle – The bundle in which to put the fragment reference.
key – The name of the entry in the bundle.
fragment – The Fragment whose reference is to be stored./**
     * Put a reference to a fragment in a Bundle.  This Bundle can be
     * persisted as saved state, and when later restoring
     * {@link #getFragment(Bundle, String)} will return the current
     * instance of the same fragment.
     *
     * @param bundle The bundle in which to put the fragment reference.
     * @param key The name of the entry in the bundle.
     * @param fragment The Fragment whose reference is to be stored.
     */
    public abstract void putFragment(Bundle bundle, String key, Fragment fragment);

    
Retrieve the current Fragment instance for a reference previously placed with putFragment(Bundle, String, Fragment). 
Params:
bundle – The bundle from which to retrieve the fragment reference.
key – The name of the entry in the bundle.
Returns:
Returns the current Fragment instance that is associated with
the given reference./**
     * Retrieve the current Fragment instance for a reference previously
     * placed with {@link #putFragment(Bundle, String, Fragment)}.
     *
     * @param bundle The bundle from which to retrieve the fragment reference.
     * @param key The name of the entry in the bundle.
     * @return Returns the current Fragment instance that is associated with
     * the given reference.
     */
    public abstract Fragment getFragment(Bundle bundle, String key);

    
Get a list of all fragments that are currently added to the FragmentManager.
This may include those that are hidden as well as those that are shown.
This will not include any fragments only in the back stack, or fragments that
are detached or removed.

The order of the fragments in the list is the order in which they were
added or attached.
Returns:
A list of all fragments that are added to the FragmentManager./**
     * Get a list of all fragments that are currently added to the FragmentManager.
     * This may include those that are hidden as well as those that are shown.
     * This will not include any fragments only in the back stack, or fragments that
     * are detached or removed.
     * <p>
     * The order of the fragments in the list is the order in which they were
     * added or attached.
     *
     * @return A list of all fragments that are added to the FragmentManager.
     */
    public abstract List<Fragment> getFragments();

    
Save the current instance state of the given Fragment.  This can be
used later when creating a new instance of the Fragment and adding
it to the fragment manager, to have it create itself to match the
current state returned here.  Note that there are limits on how
this can be used:

The Fragment must currently be attached to the FragmentManager.
A new Fragment created using this saved state must be the same class
type as the Fragment it was created from.
The saved state can not contain dependencies on other fragments -- that is it can't use putFragment(Bundle, String, Fragment) to store a fragment reference because that reference may not be valid when this saved state is later used. Likewise the Fragment's target and result code are not included in this state. 
Params:
f – The Fragment whose state is to be saved.
Returns:
The generated state.  This will be null if there was no
interesting state created by the fragment./**
     * Save the current instance state of the given Fragment.  This can be
     * used later when creating a new instance of the Fragment and adding
     * it to the fragment manager, to have it create itself to match the
     * current state returned here.  Note that there are limits on how
     * this can be used:
     *
     * <ul>
     * <li>The Fragment must currently be attached to the FragmentManager.
     * <li>A new Fragment created using this saved state must be the same class
     * type as the Fragment it was created from.
     * <li>The saved state can not contain dependencies on other fragments --
     * that is it can't use {@link #putFragment(Bundle, String, Fragment)} to
     * store a fragment reference because that reference may not be valid when
     * this saved state is later used.  Likewise the Fragment's target and
     * result code are not included in this state.
     * </ul>
     *
     * @param f The Fragment whose state is to be saved.
     * @return The generated state.  This will be null if there was no
     * interesting state created by the fragment.
     */
    public abstract Fragment.SavedState saveFragmentInstanceState(Fragment f);

    
Returns true if the final Activity.onDestroy() call has been made on the FragmentManager's Activity, so this instance is now dead. /**
     * Returns true if the final {@link Activity#onDestroy() Activity.onDestroy()}
     * call has been made on the FragmentManager's Activity, so this instance is now dead.
     */
    public abstract boolean isDestroyed();

    
Registers a FragmentLifecycleCallbacks to listen to fragment lifecycle events happening in this FragmentManager. All registered callbacks will be automatically unregistered when this FragmentManager is destroyed. 
Params:
cb – Callbacks to register
recursive – true to automatically register this callback for all child FragmentManagers/**
     * Registers a {@link FragmentLifecycleCallbacks} to listen to fragment lifecycle events
     * happening in this FragmentManager. All registered callbacks will be automatically
     * unregistered when this FragmentManager is destroyed.
     *
     * @param cb Callbacks to register
     * @param recursive true to automatically register this callback for all child FragmentManagers
     */
    public abstract void registerFragmentLifecycleCallbacks(FragmentLifecycleCallbacks cb,
            boolean recursive);

    
Unregisters a previously registered FragmentLifecycleCallbacks. If the callback was not previously registered this call has no effect. All registered callbacks will be automatically unregistered when this FragmentManager is destroyed. 
Params:
cb – Callbacks to unregister/**
     * Unregisters a previously registered {@link FragmentLifecycleCallbacks}. If the callback
     * was not previously registered this call has no effect. All registered callbacks will be
     * automatically unregistered when this FragmentManager is destroyed.
     *
     * @param cb Callbacks to unregister
     */
    public abstract void unregisterFragmentLifecycleCallbacks(FragmentLifecycleCallbacks cb);

    
Return the currently active primary navigation fragment for this FragmentManager.
The primary navigation fragment's child FragmentManager will be called first to process delegated navigation actions such as popBackStack() if no ID or transaction name is provided to pop to.
Returns:
the fragment designated as the primary navigation fragment/**
     * Return the currently active primary navigation fragment for this FragmentManager.
     *
     * <p>The primary navigation fragment's
     * {@link Fragment#getChildFragmentManager() child FragmentManager} will be called first
     * to process delegated navigation actions such as {@link #popBackStack()} if no ID
     * or transaction name is provided to pop to.</p>
     *
     * @return the fragment designated as the primary navigation fragment
     */
    public abstract Fragment getPrimaryNavigationFragment();

    
Print the FragmentManager's state into the given stream.
Params:
prefix – Text to print at the front of each line.
fd – The raw file descriptor that the dump is being sent to.
writer – A PrintWriter to which the dump is to be set.
args – Additional arguments to the dump request./**
     * Print the FragmentManager's state into the given stream.
     *
     * @param prefix Text to print at the front of each line.
     * @param fd The raw file descriptor that the dump is being sent to.
     * @param writer A PrintWriter to which the dump is to be set.
     * @param args Additional arguments to the dump request.
     */
    public abstract void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args);

    
Control whether the framework's internal fragment manager debugging
logs are turned on.  If enabled, you will see output in logcat as
the framework performs fragment operations.
/**
     * Control whether the framework's internal fragment manager debugging
     * logs are turned on.  If enabled, you will see output in logcat as
     * the framework performs fragment operations.
     */
    public static void enableDebugLogging(boolean enabled) {
        FragmentManagerImpl.DEBUG = enabled;
    }

    
Invalidate the attached activity's options menu as necessary.
This may end up being deferred until we move to the resumed state.
/**
     * Invalidate the attached activity's options menu as necessary.
     * This may end up being deferred until we move to the resumed state.
     */
    public void invalidateOptionsMenu() { }

    
Returns true if the FragmentManager's state has already been saved by its host. Any operations that would change saved state should not be performed if this method returns true. For example, any popBackStack() method, such as popBackStackImmediate() or any FragmentTransaction using FragmentTransaction.commit() instead of FragmentTransaction.commitAllowingStateLoss() will change the state and will result in an error. 
Returns:
true if this FragmentManager's state has already been saved by its host/**
     * Returns {@code true} if the FragmentManager's state has already been saved
     * by its host. Any operations that would change saved state should not be performed
     * if this method returns true. For example, any popBackStack() method, such as
     * {@link #popBackStackImmediate()} or any FragmentTransaction using
     * {@link FragmentTransaction#commit()} instead of
     * {@link FragmentTransaction#commitAllowingStateLoss()} will change
     * the state and will result in an error.
     *
     * @return true if this FragmentManager's state has already been saved by its host
     */
    public abstract boolean isStateSaved();

    
Callback interface for listening to fragment state changes that happen
within a given FragmentManager.
Deprecated:
Use the 
     Support Library FragmentLifecycleCallbacks/**
     * Callback interface for listening to fragment state changes that happen
     * within a given FragmentManager.
     *
     * @deprecated Use the <a href="{@docRoot}tools/extras/support-library.html">
     *      Support Library</a>
     *      {@link android.support.v4.app.FragmentManager.FragmentLifecycleCallbacks}
     */
    @Deprecated
    public abstract static class FragmentLifecycleCallbacks {
        
Called right before the fragment's Fragment.onAttach(Context) method is called. This is a good time to inject any required dependencies for the fragment before any of the fragment's lifecycle methods are invoked. 
Params:
fm – Host FragmentManager
f – Fragment changing state
context – Context that the Fragment is being attached to/**
         * Called right before the fragment's {@link Fragment#onAttach(Context)} method is called.
         * This is a good time to inject any required dependencies for the fragment before any of
         * the fragment's lifecycle methods are invoked.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param context Context that the Fragment is being attached to
         */
        public void onFragmentPreAttached(FragmentManager fm, Fragment f, Context context) {}

        
Called after the fragment has been attached to its host. Its host will have had
onAttachFragment called before this call happens.
Params:
fm – Host FragmentManager
f – Fragment changing state
context – Context that the Fragment was attached to/**
         * Called after the fragment has been attached to its host. Its host will have had
         * <code>onAttachFragment</code> called before this call happens.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param context Context that the Fragment was attached to
         */
        public void onFragmentAttached(FragmentManager fm, Fragment f, Context context) {}

        
Called right before the fragment's Fragment.onCreate(Bundle) method is called. This is a good time to inject any required dependencies or perform other configuration for the fragment. 
Params:
fm – Host FragmentManager
f – Fragment changing state
savedInstanceState – Saved instance bundle from a previous instance/**
         * Called right before the fragment's {@link Fragment#onCreate(Bundle)} method is called.
         * This is a good time to inject any required dependencies or perform other configuration
         * for the fragment.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param savedInstanceState Saved instance bundle from a previous instance
         */
        public void onFragmentPreCreated(FragmentManager fm, Fragment f,
                Bundle savedInstanceState) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onCreate(Bundle). This will only happen once for any given fragment instance, though the fragment may be attached and detached multiple times. 
Params:
fm – Host FragmentManager
f – Fragment changing state
savedInstanceState – Saved instance bundle from a previous instance/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onCreate(Bundle)}. This will only happen once for any given
         * fragment instance, though the fragment may be attached and detached multiple times.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param savedInstanceState Saved instance bundle from a previous instance
         */
        public void onFragmentCreated(FragmentManager fm, Fragment f, Bundle savedInstanceState) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onActivityCreated(Bundle). This will only happen once for any given fragment instance, though the fragment may be attached and detached multiple times. 
Params:
fm – Host FragmentManager
f – Fragment changing state
savedInstanceState – Saved instance bundle from a previous instance/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onActivityCreated(Bundle)}. This will only happen once for any given
         * fragment instance, though the fragment may be attached and detached multiple times.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param savedInstanceState Saved instance bundle from a previous instance
         */
        public void onFragmentActivityCreated(FragmentManager fm, Fragment f,
                Bundle savedInstanceState) {}

        
Called after the fragment has returned a non-null view from the FragmentManager's request to Fragment.onCreateView(LayoutInflater, ViewGroup, Bundle). 
Params:
fm – Host FragmentManager
f – Fragment that created and owns the view
v – View returned by the fragment
savedInstanceState – Saved instance bundle from a previous instance/**
         * Called after the fragment has returned a non-null view from the FragmentManager's
         * request to {@link Fragment#onCreateView(LayoutInflater, ViewGroup, Bundle)}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment that created and owns the view
         * @param v View returned by the fragment
         * @param savedInstanceState Saved instance bundle from a previous instance
         */
        public void onFragmentViewCreated(FragmentManager fm, Fragment f, View v,
                Bundle savedInstanceState) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onStart(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onStart()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentStarted(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onResume(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onResume()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentResumed(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onPause(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onPause()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentPaused(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onStop(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onStop()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentStopped(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onSaveInstanceState(Bundle). 
Params:
fm – Host FragmentManager
f – Fragment changing state
outState – Saved state bundle for the fragment/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onSaveInstanceState(Bundle)}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         * @param outState Saved state bundle for the fragment
         */
        public void onFragmentSaveInstanceState(FragmentManager fm, Fragment f, Bundle outState) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onDestroyView(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onDestroyView()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentViewDestroyed(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onDestroy(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onDestroy()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentDestroyed(FragmentManager fm, Fragment f) {}

        
Called after the fragment has returned from the FragmentManager's call to Fragment.onDetach(). 
Params:
fm – Host FragmentManager
f – Fragment changing state/**
         * Called after the fragment has returned from the FragmentManager's call to
         * {@link Fragment#onDetach()}.
         *
         * @param fm Host FragmentManager
         * @param f Fragment changing state
         */
        public void onFragmentDetached(FragmentManager fm, Fragment f) {}
    }
}

final class FragmentManagerState implements Parcelable {
    FragmentState[] mActive;
    int[] mAdded;
    BackStackState[] mBackStack;
    int mPrimaryNavActiveIndex = -1;
    int mNextFragmentIndex;
    
    public FragmentManagerState() {
    }
    
    public FragmentManagerState(Parcel in) {
        mActive = in.createTypedArray(FragmentState.CREATOR);
        mAdded = in.createIntArray();
        mBackStack = in.createTypedArray(BackStackState.CREATOR);
        mPrimaryNavActiveIndex = in.readInt();
        mNextFragmentIndex = in.readInt();
    }
    
    public int describeContents() {
        return 0;
    }

    public void writeToParcel(Parcel dest, int flags) {
        dest.writeTypedArray(mActive, flags);
        dest.writeIntArray(mAdded);
        dest.writeTypedArray(mBackStack, flags);
        dest.writeInt(mPrimaryNavActiveIndex);
        dest.writeInt(mNextFragmentIndex);
    }
    
    public static final Parcelable.Creator<FragmentManagerState> CREATOR
            = new Parcelable.Creator<FragmentManagerState>() {
        public FragmentManagerState createFromParcel(Parcel in) {
            return new FragmentManagerState(in);
        }
        
        public FragmentManagerState[] newArray(int size) {
            return new FragmentManagerState[size];
        }
    };
}

Container for fragments associated with an activity.
/**
 * Container for fragments associated with an activity.
 */
final class FragmentManagerImpl extends FragmentManager implements LayoutInflater.Factory2 {
    static boolean DEBUG = false;
    static final String TAG = "FragmentManager";
    
    static final String TARGET_REQUEST_CODE_STATE_TAG = "android:target_req_state";
    static final String TARGET_STATE_TAG = "android:target_state";
    static final String VIEW_STATE_TAG = "android:view_state";
    static final String USER_VISIBLE_HINT_TAG = "android:user_visible_hint";

    static class AnimateOnHWLayerIfNeededListener implements Animator.AnimatorListener {
        private boolean mShouldRunOnHWLayer = false;
        private View mView;
        public AnimateOnHWLayerIfNeededListener(final View v) {
            if (v == null) {
                return;
            }
            mView = v;
        }

        @Override
        public void onAnimationStart(Animator animation) {
            mShouldRunOnHWLayer = shouldRunOnHWLayer(mView, animation);
            if (mShouldRunOnHWLayer) {
                mView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
            }
        }

        @Override
        public void onAnimationEnd(Animator animation) {
            if (mShouldRunOnHWLayer) {
                mView.setLayerType(View.LAYER_TYPE_NONE, null);
            }
            mView = null;
            animation.removeListener(this);
        }

        @Override
        public void onAnimationCancel(Animator animation) {

        }

        @Override
        public void onAnimationRepeat(Animator animation) {

        }
    }

    ArrayList<OpGenerator> mPendingActions;
    boolean mExecutingActions;

    int mNextFragmentIndex = 0;
    SparseArray<Fragment> mActive;
    final ArrayList<Fragment> mAdded = new ArrayList<>();
    ArrayList<BackStackRecord> mBackStack;
    ArrayList<Fragment> mCreatedMenus;
    
    // Must be accessed while locked.
    ArrayList<BackStackRecord> mBackStackIndices;
    ArrayList<Integer> mAvailBackStackIndices;

    ArrayList<OnBackStackChangedListener> mBackStackChangeListeners;
    final CopyOnWriteArrayList<Pair<FragmentLifecycleCallbacks, Boolean>>
            mLifecycleCallbacks = new CopyOnWriteArrayList<>();

    int mCurState = Fragment.INITIALIZING;
    FragmentHostCallback<?> mHost;
    FragmentContainer mContainer;
    Fragment mParent;
    Fragment mPrimaryNav;
    
    boolean mNeedMenuInvalidate;
    boolean mStateSaved;
    boolean mDestroyed;
    String mNoTransactionsBecause;
    boolean mHavePendingDeferredStart;

    // Temporary vars for removing redundant operations in BackStackRecords:
    ArrayList<BackStackRecord> mTmpRecords;
    ArrayList<Boolean> mTmpIsPop;
    ArrayList<Fragment> mTmpAddedFragments;

    // Temporary vars for state save and restore.
    Bundle mStateBundle = null;
    SparseArray<Parcelable> mStateArray = null;

    // Postponed transactions.
    ArrayList<StartEnterTransitionListener> mPostponedTransactions;

    // Prior to O, we allowed executing transactions during fragment manager state changes.
    // This is dangerous, but we want to keep from breaking old applications.
    boolean mAllowOldReentrantBehavior;

    // Saved FragmentManagerNonConfig during saveAllState() and cleared in noteStateNotSaved()
    FragmentManagerNonConfig mSavedNonConfig;

    Runnable mExecCommit = new Runnable() {
        @Override
        public void run() {
            execPendingActions();
        }
    };

    private void throwException(RuntimeException ex) {
        Log.e(TAG, ex.getMessage());
        LogWriter logw = new LogWriter(Log.ERROR, TAG);
        PrintWriter pw = new FastPrintWriter(logw, false, 1024);
        if (mHost != null) {
            Log.e(TAG, "Activity state:");
            try {
                mHost.onDump("  ", null, pw, new String[] { });
            } catch (Exception e) {
                pw.flush();
                Log.e(TAG, "Failed dumping state", e);
            }
        } else {
            Log.e(TAG, "Fragment manager state:");
            try {
                dump("  ", null, pw, new String[] { });
            } catch (Exception e) {
                pw.flush();
                Log.e(TAG, "Failed dumping state", e);
            }
        }
        pw.flush();
        throw ex;
    }

    static boolean modifiesAlpha(Animator anim) {
        if (anim == null) {
            return false;
        }
        if (anim instanceof ValueAnimator) {
            ValueAnimator valueAnim = (ValueAnimator) anim;
            PropertyValuesHolder[] values = valueAnim.getValues();
            for (int i = 0; i < values.length; i++) {
                if (("alpha").equals(values[i].getPropertyName())) {
                    return true;
                }
            }
        } else if (anim instanceof AnimatorSet) {
            List<Animator> animList = ((AnimatorSet) anim).getChildAnimations();
            for (int i = 0; i < animList.size(); i++) {
                if (modifiesAlpha(animList.get(i))) {
                    return true;
                }
            }
        }
        return false;
    }

    static boolean shouldRunOnHWLayer(View v, Animator anim) {
        if (v == null || anim == null) {
            return false;
        }
        return v.getLayerType() == View.LAYER_TYPE_NONE
                && v.hasOverlappingRendering()
                && modifiesAlpha(anim);
    }

    
Sets the to be animated view on hardware layer during the animation.
/**
     * Sets the to be animated view on hardware layer during the animation.
     */
    private void setHWLayerAnimListenerIfAlpha(final View v, Animator anim) {
        if (v == null || anim == null) {
            return;
        }
        if (shouldRunOnHWLayer(v, anim)) {
            anim.addListener(new AnimateOnHWLayerIfNeededListener(v));
        }
    }

    @Override
    public FragmentTransaction beginTransaction() {
        return new BackStackRecord(this);
    }

    @Override
    public boolean executePendingTransactions() {
        boolean updates = execPendingActions();
        forcePostponedTransactions();
        return updates;
    }

    @Override
    public void popBackStack() {
        enqueueAction(new PopBackStackState(null, -1, 0), false);
    }

    @Override
    public boolean popBackStackImmediate() {
        checkStateLoss();
        return popBackStackImmediate(null, -1, 0);
    }

    @Override
    public void popBackStack(String name, int flags) {
        enqueueAction(new PopBackStackState(name, -1, flags), false);
    }

    @Override
    public boolean popBackStackImmediate(String name, int flags) {
        checkStateLoss();
        return popBackStackImmediate(name, -1, flags);
    }

    @Override
    public void popBackStack(int id, int flags) {
        if (id < 0) {
            throw new IllegalArgumentException("Bad id: " + id);
        }
        enqueueAction(new PopBackStackState(null, id, flags), false);
    }

    @Override
    public boolean popBackStackImmediate(int id, int flags) {
        checkStateLoss();
        if (id < 0) {
            throw new IllegalArgumentException("Bad id: " + id);
        }
        return popBackStackImmediate(null, id, flags);
    }

    
Used by all public popBackStackImmediate methods, this executes pending transactions and
returns true if the pop action did anything, regardless of what other pending
transactions did.
Returns:
true if the pop operation did anything or false otherwise./**
     * Used by all public popBackStackImmediate methods, this executes pending transactions and
     * returns true if the pop action did anything, regardless of what other pending
     * transactions did.
     *
     * @return true if the pop operation did anything or false otherwise.
     */
    private boolean popBackStackImmediate(String name, int id, int flags) {
        execPendingActions();
        ensureExecReady(true);

        if (mPrimaryNav != null // We have a primary nav fragment
                && id < 0 // No valid id (since they're local)
                && name == null) { // no name to pop to (since they're local)
            final FragmentManager childManager = mPrimaryNav.mChildFragmentManager;
            if (childManager != null && childManager.popBackStackImmediate()) {
                // We did something, just not to this specific FragmentManager. Return true.
                return true;
            }
        }

        boolean executePop = popBackStackState(mTmpRecords, mTmpIsPop, name, id, flags);
        if (executePop) {
            mExecutingActions = true;
            try {
                removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop);
            } finally {
                cleanupExec();
            }
        }

        doPendingDeferredStart();
        burpActive();
        return executePop;
    }

    @Override
    public int getBackStackEntryCount() {
        return mBackStack != null ? mBackStack.size() : 0;
    }

    @Override
    public BackStackEntry getBackStackEntryAt(int index) {
        return mBackStack.get(index);
    }

    @Override
    public void addOnBackStackChangedListener(OnBackStackChangedListener listener) {
        if (mBackStackChangeListeners == null) {
            mBackStackChangeListeners = new ArrayList<OnBackStackChangedListener>();
        }
        mBackStackChangeListeners.add(listener);
    }

    @Override
    public void removeOnBackStackChangedListener(OnBackStackChangedListener listener) {
        if (mBackStackChangeListeners != null) {
            mBackStackChangeListeners.remove(listener);
        }
    }

    @Override
    public void putFragment(Bundle bundle, String key, Fragment fragment) {
        if (fragment.mIndex < 0) {
            throwException(new IllegalStateException("Fragment " + fragment
                    + " is not currently in the FragmentManager"));
        }
        bundle.putInt(key, fragment.mIndex);
    }

    @Override
    public Fragment getFragment(Bundle bundle, String key) {
        int index = bundle.getInt(key, -1);
        if (index == -1) {
            return null;
        }
        Fragment f = mActive.get(index);
        if (f == null) {
            throwException(new IllegalStateException("Fragment no longer exists for key "
                    + key + ": index " + index));
        }
        return f;
    }

    @Override
    public List<Fragment> getFragments() {
        if (mAdded.isEmpty()) {
            return Collections.EMPTY_LIST;
        }
        synchronized (mAdded) {
            return (List<Fragment>) mAdded.clone();
        }
    }

    @Override
    public Fragment.SavedState saveFragmentInstanceState(Fragment fragment) {
        if (fragment.mIndex < 0) {
            throwException(new IllegalStateException("Fragment " + fragment
                    + " is not currently in the FragmentManager"));
        }
        if (fragment.mState > Fragment.INITIALIZING) {
            Bundle result = saveFragmentBasicState(fragment);
            return result != null ? new Fragment.SavedState(result) : null;
        }
        return null;
    }

    @Override
    public boolean isDestroyed() {
        return mDestroyed;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(128);
        sb.append("FragmentManager{");
        sb.append(Integer.toHexString(System.identityHashCode(this)));
        sb.append(" in ");
        if (mParent != null) {
            DebugUtils.buildShortClassTag(mParent, sb);
        } else {
            DebugUtils.buildShortClassTag(mHost, sb);
        }
        sb.append("}}");
        return sb.toString();
    }

    @Override
    public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
        String innerPrefix = prefix + "    ";

        int N;
        if (mActive != null) {
            N = mActive.size();
            if (N > 0) {
                writer.print(prefix); writer.print("Active Fragments in ");
                        writer.print(Integer.toHexString(System.identityHashCode(this)));
                        writer.println(":");
                for (int i=0; i<N; i++) {
                    Fragment f = mActive.valueAt(i);
                    writer.print(prefix); writer.print("  #"); writer.print(i);
                            writer.print(": "); writer.println(f);
                    if (f != null) {
                        f.dump(innerPrefix, fd, writer, args);
                    }
                }
            }
        }

        N = mAdded.size();
        if (N > 0) {
            writer.print(prefix);
            writer.println("Added Fragments:");
            for (int i = 0; i < N; i++) {
                Fragment f = mAdded.get(i);
                writer.print(prefix);
                writer.print("  #");
                writer.print(i);
                writer.print(": ");
                writer.println(f.toString());
            }
        }

        if (mCreatedMenus != null) {
            N = mCreatedMenus.size();
            if (N > 0) {
                writer.print(prefix); writer.println("Fragments Created Menus:");
                for (int i=0; i<N; i++) {
                    Fragment f = mCreatedMenus.get(i);
                    writer.print(prefix); writer.print("  #"); writer.print(i);
                            writer.print(": "); writer.println(f.toString());
                }
            }
        }

        if (mBackStack != null) {
            N = mBackStack.size();
            if (N > 0) {
                writer.print(prefix); writer.println("Back Stack:");
                for (int i=0; i<N; i++) {
                    BackStackRecord bs = mBackStack.get(i);
                    writer.print(prefix); writer.print("  #"); writer.print(i);
                            writer.print(": "); writer.println(bs.toString());
                    bs.dump(innerPrefix, fd, writer, args);
                }
            }
        }

        synchronized (this) {
            if (mBackStackIndices != null) {
                N = mBackStackIndices.size();
                if (N > 0) {
                    writer.print(prefix); writer.println("Back Stack Indices:");
                    for (int i=0; i<N; i++) {
                        BackStackRecord bs = mBackStackIndices.get(i);
                        writer.print(prefix); writer.print("  #"); writer.print(i);
                                writer.print(": "); writer.println(bs);
                    }
                }
            }

            if (mAvailBackStackIndices != null && mAvailBackStackIndices.size() > 0) {
                writer.print(prefix); writer.print("mAvailBackStackIndices: ");
                        writer.println(Arrays.toString(mAvailBackStackIndices.toArray()));
            }
        }

        if (mPendingActions != null) {
            N = mPendingActions.size();
            if (N > 0) {
                writer.print(prefix); writer.println("Pending Actions:");
                for (int i=0; i<N; i++) {
                    OpGenerator r = mPendingActions.get(i);
                    writer.print(prefix); writer.print("  #"); writer.print(i);
                            writer.print(": "); writer.println(r);
                }
            }
        }

        writer.print(prefix); writer.println("FragmentManager misc state:");
        writer.print(prefix); writer.print("  mHost="); writer.println(mHost);
        writer.print(prefix); writer.print("  mContainer="); writer.println(mContainer);
        if (mParent != null) {
            writer.print(prefix); writer.print("  mParent="); writer.println(mParent);
        }
        writer.print(prefix); writer.print("  mCurState="); writer.print(mCurState);
                writer.print(" mStateSaved="); writer.print(mStateSaved);
                writer.print(" mDestroyed="); writer.println(mDestroyed);
        if (mNeedMenuInvalidate) {
            writer.print(prefix); writer.print("  mNeedMenuInvalidate=");
                    writer.println(mNeedMenuInvalidate);
        }
        if (mNoTransactionsBecause != null) {
            writer.print(prefix); writer.print("  mNoTransactionsBecause=");
                    writer.println(mNoTransactionsBecause);
        }
    }

    Animator loadAnimator(Fragment fragment, int transit, boolean enter,
            int transitionStyle) {
        Animator animObj = fragment.onCreateAnimator(transit, enter, fragment.getNextAnim());
        if (animObj != null) {
            return animObj;
        }
        
        if (fragment.getNextAnim() != 0) {
            Animator anim = AnimatorInflater.loadAnimator(mHost.getContext(),
                    fragment.getNextAnim());
            if (anim != null) {
                return anim;
            }
        }
        
        if (transit == 0) {
            return null;
        }
        
        int styleIndex = transitToStyleIndex(transit, enter);
        if (styleIndex < 0) {
            return null;
        }
        
        if (transitionStyle == 0 && mHost.onHasWindowAnimations()) {
            transitionStyle = mHost.onGetWindowAnimations();
        }
        if (transitionStyle == 0) {
            return null;
        }
        
        TypedArray attrs = mHost.getContext().obtainStyledAttributes(transitionStyle,
                com.android.internal.R.styleable.FragmentAnimation);
        int anim = attrs.getResourceId(styleIndex, 0);
        attrs.recycle();
        
        if (anim == 0) {
            return null;
        }
        
        return AnimatorInflater.loadAnimator(mHost.getContext(), anim);
    }
    
    public void performPendingDeferredStart(Fragment f) {
        if (f.mDeferStart) {
            if (mExecutingActions) {
                // Wait until we're done executing our pending transactions
                mHavePendingDeferredStart = true;
                return;
            }
            f.mDeferStart = false;
            moveToState(f, mCurState, 0, 0, false);
        }
    }

    boolean isStateAtLeast(int state) {
        return mCurState >= state;
    }

    @SuppressWarnings("ReferenceEquality")
    void moveToState(Fragment f, int newState, int transit, int transitionStyle,
            boolean keepActive) {
        if (DEBUG && false) Log.v(TAG, "moveToState: " + f
            + " oldState=" + f.mState + " newState=" + newState
            + " mRemoving=" + f.mRemoving + " Callers=" + Debug.getCallers(5));

        // Fragments that are not currently added will sit in the onCreate() state.
        if ((!f.mAdded || f.mDetached) && newState > Fragment.CREATED) {
            newState = Fragment.CREATED;
        }
        if (f.mRemoving && newState > f.mState) {
            if (f.mState == Fragment.INITIALIZING && f.isInBackStack()) {
                // Allow the fragment to be created so that it can be saved later.
                newState = Fragment.CREATED;
            } else {
                // While removing a fragment, we can't change it to a higher state.
                newState = f.mState;
            }
        }
        // Defer start if requested; don't allow it to move to STARTED or higher
        // if it's not already started.
        if (f.mDeferStart && f.mState < Fragment.STARTED && newState > Fragment.STOPPED) {
            newState = Fragment.STOPPED;
        }
        if (f.mState <= newState) {
            // For fragments that are created from a layout, when restoring from
            // state we don't want to allow them to be created until they are
            // being reloaded from the layout.
            if (f.mFromLayout && !f.mInLayout) {
                return;
            }
            if (f.getAnimatingAway() != null) {
                // The fragment is currently being animated...  but!  Now we
                // want to move our state back up.  Give up on waiting for the
                // animation, move to whatever the final state should be once
                // the animation is done, and then we can proceed from there.
                f.setAnimatingAway(null);
                moveToState(f, f.getStateAfterAnimating(), 0, 0, true);
            }
            switch (f.mState) {
                case Fragment.INITIALIZING:
                    if (newState > Fragment.INITIALIZING) {
                        if (DEBUG) Log.v(TAG, "moveto CREATED: " + f);
                        if (f.mSavedFragmentState != null) {
                            f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray(
                                    FragmentManagerImpl.VIEW_STATE_TAG);
                            f.mTarget = getFragment(f.mSavedFragmentState,
                                    FragmentManagerImpl.TARGET_STATE_TAG);
                            if (f.mTarget != null) {
                                f.mTargetRequestCode = f.mSavedFragmentState.getInt(
                                        FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0);
                            }
                            f.mUserVisibleHint = f.mSavedFragmentState.getBoolean(
                                    FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true);
                            if (!f.mUserVisibleHint) {
                                f.mDeferStart = true;
                                if (newState > Fragment.STOPPED) {
                                    newState = Fragment.STOPPED;
                                }
                            }
                        }

                        f.mHost = mHost;
                        f.mParentFragment = mParent;
                        f.mFragmentManager = mParent != null
                                ? mParent.mChildFragmentManager : mHost.getFragmentManagerImpl();

                        // If we have a target fragment, push it along to at least CREATED
                        // so that this one can rely on it as an initialized dependency.
                        if (f.mTarget != null) {
                            if (mActive.get(f.mTarget.mIndex) != f.mTarget) {
                                throw new IllegalStateException("Fragment " + f
                                        + " declared target fragment " + f.mTarget
                                        + " that does not belong to this FragmentManager!");
                            }
                            if (f.mTarget.mState < Fragment.CREATED) {
                                moveToState(f.mTarget, Fragment.CREATED, 0, 0, true);
                            }
                        }

                        dispatchOnFragmentPreAttached(f, mHost.getContext(), false);
                        f.mCalled = false;
                        f.onAttach(mHost.getContext());
                        if (!f.mCalled) {
                            throw new SuperNotCalledException("Fragment " + f
                                    + " did not call through to super.onAttach()");
                        }
                        if (f.mParentFragment == null) {
                            mHost.onAttachFragment(f);
                        } else {
                            f.mParentFragment.onAttachFragment(f);
                        }
                        dispatchOnFragmentAttached(f, mHost.getContext(), false);

                        if (!f.mIsCreated) {
                            dispatchOnFragmentPreCreated(f, f.mSavedFragmentState, false);
                            f.performCreate(f.mSavedFragmentState);
                            dispatchOnFragmentCreated(f, f.mSavedFragmentState, false);
                        } else {
                            f.restoreChildFragmentState(f.mSavedFragmentState, true);
                            f.mState = Fragment.CREATED;
                        }
                        f.mRetaining = false;
                    }
                    // fall through
                case Fragment.CREATED:
                    // This is outside the if statement below on purpose; we want this to run
                    // even if we do a moveToState from CREATED => *, CREATED => CREATED, and
                    // * => CREATED as part of the case fallthrough above.
                    ensureInflatedFragmentView(f);

                    if (newState > Fragment.CREATED) {
                        if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f);
                        if (!f.mFromLayout) {
                            ViewGroup container = null;
                            if (f.mContainerId != 0) {
                                if (f.mContainerId == View.NO_ID) {
                                    throwException(new IllegalArgumentException(
                                            "Cannot create fragment "
                                                    + f
                                                    + " for a container view with no id"));
                                }
                                container = mContainer.onFindViewById(f.mContainerId);
                                if (container == null && !f.mRestored) {
                                    String resName;
                                    try {
                                        resName = f.getResources().getResourceName(f.mContainerId);
                                    } catch (NotFoundException e) {
                                        resName = "unknown";
                                    }
                                    throwException(new IllegalArgumentException(
                                            "No view found for id 0x"
                                            + Integer.toHexString(f.mContainerId) + " ("
                                            + resName
                                            + ") for fragment " + f));
                                }
                            }
                            f.mContainer = container;
                            f.mView = f.performCreateView(f.performGetLayoutInflater(
                                    f.mSavedFragmentState), container, f.mSavedFragmentState);
                            if (f.mView != null) {
                                f.mView.setSaveFromParentEnabled(false);
                                if (container != null) {
                                    container.addView(f.mView);
                                }
                                if (f.mHidden) {
                                    f.mView.setVisibility(View.GONE);
                                }
                                f.onViewCreated(f.mView, f.mSavedFragmentState);
                                dispatchOnFragmentViewCreated(f, f.mView, f.mSavedFragmentState,
                                        false);
                                // Only animate the view if it is visible. This is done after
                                // dispatchOnFragmentViewCreated in case visibility is changed
                                f.mIsNewlyAdded = (f.mView.getVisibility() == View.VISIBLE)
                                        && f.mContainer != null;
                            }
                        }

                        f.performActivityCreated(f.mSavedFragmentState);
                        dispatchOnFragmentActivityCreated(f, f.mSavedFragmentState, false);
                        if (f.mView != null) {
                            f.restoreViewState(f.mSavedFragmentState);
                        }
                        f.mSavedFragmentState = null;
                    }
                    // fall through
                case Fragment.ACTIVITY_CREATED:
                    if (newState > Fragment.ACTIVITY_CREATED) {
                        f.mState = Fragment.STOPPED;
                    }
                    // fall through
                case Fragment.STOPPED:
                    if (newState > Fragment.STOPPED) {
                        if (DEBUG) Log.v(TAG, "moveto STARTED: " + f);
                        f.performStart();
                        dispatchOnFragmentStarted(f, false);
                    }
                    // fall through
                case Fragment.STARTED:
                    if (newState > Fragment.STARTED) {
                        if (DEBUG) Log.v(TAG, "moveto RESUMED: " + f);
                        f.performResume();
                        dispatchOnFragmentResumed(f, false);
                        // Get rid of this in case we saved it and never needed it.
                        f.mSavedFragmentState = null;
                        f.mSavedViewState = null;
                    }
            }
        } else if (f.mState > newState) {
            switch (f.mState) {
                case Fragment.RESUMED:
                    if (newState < Fragment.RESUMED) {
                        if (DEBUG) Log.v(TAG, "movefrom RESUMED: " + f);
                        f.performPause();
                        dispatchOnFragmentPaused(f, false);
                    }
                    // fall through
                case Fragment.STARTED:
                    if (newState < Fragment.STARTED) {
                        if (DEBUG) Log.v(TAG, "movefrom STARTED: " + f);
                        f.performStop();
                        dispatchOnFragmentStopped(f, false);
                    }
                    // fall through
                case Fragment.STOPPED:
                case Fragment.ACTIVITY_CREATED:
                    if (newState < Fragment.ACTIVITY_CREATED) {
                        if (DEBUG) Log.v(TAG, "movefrom ACTIVITY_CREATED: " + f);
                        if (f.mView != null) {
                            // Need to save the current view state if not
                            // done already.
                            if (mHost.onShouldSaveFragmentState(f) && f.mSavedViewState == null) {
                                saveFragmentViewState(f);
                            }
                        }
                        f.performDestroyView();
                        dispatchOnFragmentViewDestroyed(f, false);
                        if (f.mView != null && f.mContainer != null) {
                            if (getTargetSdk() >= Build.VERSION_CODES.O) {
                                // Stop any current animations:
                                f.mView.clearAnimation();
                                f.mContainer.endViewTransition(f.mView);
                            }
                            Animator anim = null;
                            if (mCurState > Fragment.INITIALIZING && !mDestroyed
                                    && f.mView.getVisibility() == View.VISIBLE
                                    && f.mView.getTransitionAlpha() > 0) {
                                anim = loadAnimator(f, transit, false,
                                        transitionStyle);
                            }
                            f.mView.setTransitionAlpha(1f);
                            if (anim != null) {
                                final ViewGroup container = f.mContainer;
                                final View view = f.mView;
                                final Fragment fragment = f;
                                container.startViewTransition(view);
                                f.setAnimatingAway(anim);
                                f.setStateAfterAnimating(newState);
                                anim.addListener(new AnimatorListenerAdapter() {
                                    @Override
                                    public void onAnimationEnd(Animator anim) {
                                        container.endViewTransition(view);
                                        Animator animator = f.getAnimatingAway();
                                        f.setAnimatingAway(null);
                                        // If the animation finished immediately, the fragment's
                                        // view will still be there. If so, we can just pretend
                                        // there was no animation and skip the moveToState()
                                        if (container.indexOfChild(view) == -1
                                                && animator != null) {
                                            moveToState(fragment, fragment.getStateAfterAnimating(),
                                                    0, 0, false);
                                        }
                                    }
                                });
                                anim.setTarget(f.mView);
                                setHWLayerAnimListenerIfAlpha(f.mView, anim);
                                anim.start();

                            }
                            f.mContainer.removeView(f.mView);
                        }
                        f.mContainer = null;
                        f.mView = null;
                        f.mInLayout = false;
                    }
                    // fall through
                case Fragment.CREATED:
                    if (newState < Fragment.CREATED) {
                        if (mDestroyed) {
                            if (f.getAnimatingAway() != null) {
                                // The fragment's containing activity is
                                // being destroyed, but this fragment is
                                // currently animating away.  Stop the
                                // animation right now -- it is not needed,
                                // and we can't wait any more on destroying
                                // the fragment.
                                Animator anim = f.getAnimatingAway();
                                f.setAnimatingAway(null);
                                anim.cancel();
                            }
                        }
                        if (f.getAnimatingAway() != null) {
                            // We are waiting for the fragment's view to finish
                            // animating away.  Just make a note of the state
                            // the fragment now should move to once the animation
                            // is done.
                            f.setStateAfterAnimating(newState);
                            newState = Fragment.CREATED;
                        } else {
                            if (DEBUG) Log.v(TAG, "movefrom CREATED: " + f);
                            if (!f.mRetaining) {
                                f.performDestroy();
                                dispatchOnFragmentDestroyed(f, false);
                            } else {
                                f.mState = Fragment.INITIALIZING;
                            }

                            f.performDetach();
                            dispatchOnFragmentDetached(f, false);
                            if (!keepActive) {
                                if (!f.mRetaining) {
                                    makeInactive(f);
                                } else {
                                    f.mHost = null;
                                    f.mParentFragment = null;
                                    f.mFragmentManager = null;
                                }
                            }
                        }
                    }
            }
        }
        
        if (f.mState != newState) {
            Log.w(TAG, "moveToState: Fragment state for " + f + " not updated inline; "
                    + "expected state " + newState + " found " + f.mState);
            f.mState = newState;
        }
    }
    
    void moveToState(Fragment f) {
        moveToState(f, mCurState, 0, 0, false);
    }

    void ensureInflatedFragmentView(Fragment f) {
        if (f.mFromLayout && !f.mPerformedCreateView) {
            f.mView = f.performCreateView(f.performGetLayoutInflater(
                    f.mSavedFragmentState), null, f.mSavedFragmentState);
            if (f.mView != null) {
                f.mView.setSaveFromParentEnabled(false);
                if (f.mHidden) f.mView.setVisibility(View.GONE);
                f.onViewCreated(f.mView, f.mSavedFragmentState);
                dispatchOnFragmentViewCreated(f, f.mView, f.mSavedFragmentState, false);
            }
        }
    }

    
Fragments that have been shown or hidden don't have their visibility changed or animations run during the showFragment(Fragment) or hideFragment(Fragment) calls. After fragments are brought to their final state in moveFragmentToExpectedState(Fragment) the fragments that have been shown or hidden must have their visibility changed and their animations started here. 
Params:
fragment – The fragment with mHiddenChanged = true that should change its View's
                visibility and start the show or hide animation./**
     * Fragments that have been shown or hidden don't have their visibility changed or
     * animations run during the {@link #showFragment(Fragment)} or {@link #hideFragment(Fragment)}
     * calls. After fragments are brought to their final state in
     * {@link #moveFragmentToExpectedState(Fragment)} the fragments that have been shown or
     * hidden must have their visibility changed and their animations started here.
     *
     * @param fragment The fragment with mHiddenChanged = true that should change its View's
     *                 visibility and start the show or hide animation.
     */
    void completeShowHideFragment(final Fragment fragment) {
        if (fragment.mView != null) {
            Animator anim = loadAnimator(fragment, fragment.getNextTransition(), !fragment.mHidden,
                    fragment.getNextTransitionStyle());
            if (anim != null) {
                anim.setTarget(fragment.mView);
                if (fragment.mHidden) {
                    if (fragment.isHideReplaced()) {
                        fragment.setHideReplaced(false);
                    } else {
                        final ViewGroup container = fragment.mContainer;
                        final View animatingView = fragment.mView;
                        if (container != null) {
                            container.startViewTransition(animatingView);
                        }
                        // Delay the actual hide operation until the animation finishes, otherwise
                        // the fragment will just immediately disappear
                        anim.addListener(new AnimatorListenerAdapter() {
                            @Override
                            public void onAnimationEnd(Animator animation) {
                                if (container != null) {
                                    container.endViewTransition(animatingView);
                                }
                                animation.removeListener(this);
                                animatingView.setVisibility(View.GONE);
                            }
                        });
                    }
                } else {
                    fragment.mView.setVisibility(View.VISIBLE);
                }
                setHWLayerAnimListenerIfAlpha(fragment.mView, anim);
                anim.start();
            } else {
                final int visibility = fragment.mHidden && !fragment.isHideReplaced()
                        ? View.GONE
                        : View.VISIBLE;
                fragment.mView.setVisibility(visibility);
                if (fragment.isHideReplaced()) {
                    fragment.setHideReplaced(false);
                }
            }
        }
        if (fragment.mAdded && fragment.mHasMenu && fragment.mMenuVisible) {
            mNeedMenuInvalidate = true;
        }
        fragment.mHiddenChanged = false;
        fragment.onHiddenChanged(fragment.mHidden);
    }

    
Moves a fragment to its expected final state or the fragment manager's state, depending
on whether the fragment manager's state is raised properly.
Params:
f – The fragment to change./**
     * Moves a fragment to its expected final state or the fragment manager's state, depending
     * on whether the fragment manager's state is raised properly.
     *
     * @param f The fragment to change.
     */
    void moveFragmentToExpectedState(final Fragment f) {
        if (f == null) {
            return;
        }
        int nextState = mCurState;
        if (f.mRemoving) {
            if (f.isInBackStack()) {
                nextState = Math.min(nextState, Fragment.CREATED);
            } else {
                nextState = Math.min(nextState, Fragment.INITIALIZING);
            }
        }

        moveToState(f, nextState, f.getNextTransition(), f.getNextTransitionStyle(), false);

        if (f.mView != null) {
            // Move the view if it is out of order
            Fragment underFragment = findFragmentUnder(f);
            if (underFragment != null) {
                final View underView = underFragment.mView;
                // make sure this fragment is in the right order.
                final ViewGroup container = f.mContainer;
                int underIndex = container.indexOfChild(underView);
                int viewIndex = container.indexOfChild(f.mView);
                if (viewIndex < underIndex) {
                    container.removeViewAt(viewIndex);
                    container.addView(f.mView, underIndex);
                }
            }
            if (f.mIsNewlyAdded && f.mContainer != null) {
                // Make it visible and run the animations
                f.mView.setTransitionAlpha(1f);
                f.mIsNewlyAdded = false;
                // run animations:
                Animator anim = loadAnimator(f, f.getNextTransition(), true, f.getNextTransitionStyle());
                if (anim != null) {
                    anim.setTarget(f.mView);
                    setHWLayerAnimListenerIfAlpha(f.mView, anim);
                    anim.start();
                }
            }
        }
        if (f.mHiddenChanged) {
            completeShowHideFragment(f);
        }
    }

    
Changes the state of the fragment manager to newState. If the fragment manager changes state or always is true, any fragments within it have their states updated as well. 
Params:
newState – The new state for the fragment manager
always – If true, all fragments update their state, even if newState matches the current fragment manager's state./**
     * Changes the state of the fragment manager to {@code newState}. If the fragment manager
     * changes state or {@code always} is {@code true}, any fragments within it have their
     * states updated as well.
     *
     * @param newState The new state for the fragment manager
     * @param always If {@code true}, all fragments update their state, even
     *               if {@code newState} matches the current fragment manager's state.
     */
    void moveToState(int newState, boolean always) {
        if (mHost == null && newState != Fragment.INITIALIZING) {
            throw new IllegalStateException("No activity");
        }

        if (!always && mCurState == newState) {
            return;
        }

        mCurState = newState;

        if (mActive != null) {
            boolean loadersRunning = false;

            // Must add them in the proper order. mActive fragments may be out of order
            final int numAdded = mAdded.size();
            for (int i = 0; i < numAdded; i++) {
                Fragment f = mAdded.get(i);
                moveFragmentToExpectedState(f);
                if (f.mLoaderManager != null) {
                    loadersRunning |= f.mLoaderManager.hasRunningLoaders();
                }
            }

            // Now iterate through all active fragments. These will include those that are removed
            // and detached.
            final int numActive = mActive.size();
            for (int i = 0; i < numActive; i++) {
                Fragment f = mActive.valueAt(i);
                if (f != null && (f.mRemoving || f.mDetached) && !f.mIsNewlyAdded) {
                    moveFragmentToExpectedState(f);
                    if (f.mLoaderManager != null) {
                        loadersRunning |= f.mLoaderManager.hasRunningLoaders();
                    }
                }
            }

            if (!loadersRunning) {
                startPendingDeferredFragments();
            }

            if (mNeedMenuInvalidate && mHost != null && mCurState == Fragment.RESUMED) {
                mHost.onInvalidateOptionsMenu();
                mNeedMenuInvalidate = false;
            }
        }
    }

    void startPendingDeferredFragments() {
        if (mActive == null) return;

        for (int i=0; i<mActive.size(); i++) {
            Fragment f = mActive.valueAt(i);
            if (f != null) {
                performPendingDeferredStart(f);
            }
        }
    }

    void makeActive(Fragment f) {
        if (f.mIndex >= 0) {
            return;
        }

        f.setIndex(mNextFragmentIndex++, mParent);
        if (mActive == null) {
            mActive = new SparseArray<>();
        }
        mActive.put(f.mIndex, f);
        if (DEBUG) Log.v(TAG, "Allocated fragment index " + f);
    }
    
    void makeInactive(Fragment f) {
        if (f.mIndex < 0) {
            return;
        }
        
        if (DEBUG) Log.v(TAG, "Freeing fragment index " + f);
        // Don't remove yet. That happens in burpActive(). This prevents
        // concurrent modification while iterating over mActive
        mActive.put(f.mIndex, null);
        mHost.inactivateFragment(f.mWho);
        f.initState();
    }
    
    public void addFragment(Fragment fragment, boolean moveToStateNow) {
        if (DEBUG) Log.v(TAG, "add: " + fragment);
        makeActive(fragment);
        if (!fragment.mDetached) {
            if (mAdded.contains(fragment)) {
                throw new IllegalStateException("Fragment already added: " + fragment);
            }
            synchronized (mAdded) {
                mAdded.add(fragment);
            }
            fragment.mAdded = true;
            fragment.mRemoving = false;
            if (fragment.mView == null) {
                fragment.mHiddenChanged = false;
            }
            if (fragment.mHasMenu && fragment.mMenuVisible) {
                mNeedMenuInvalidate = true;
            }
            if (moveToStateNow) {
                moveToState(fragment);
            }
        }
    }

    public void removeFragment(Fragment fragment) {
        if (DEBUG) Log.v(TAG, "remove: " + fragment + " nesting=" + fragment.mBackStackNesting);
        final boolean inactive = !fragment.isInBackStack();
        if (!fragment.mDetached || inactive) {
            if (false) {
                // Would be nice to catch a bad remove here, but we need
                // time to test this to make sure we aren't crashes cases
                // where it is not a problem.
                if (!mAdded.contains(fragment)) {
                    throw new IllegalStateException("Fragment not added: " + fragment);
                }
            }
            synchronized (mAdded) {
                mAdded.remove(fragment);
            }
            if (fragment.mHasMenu && fragment.mMenuVisible) {
                mNeedMenuInvalidate = true;
            }
            fragment.mAdded = false;
            fragment.mRemoving = true;
        }
    }

    
Marks a fragment as hidden to be later animated in with completeShowHideFragment(Fragment). 
Params:
fragment – The fragment to be shown./**
     * Marks a fragment as hidden to be later animated in with
     * {@link #completeShowHideFragment(Fragment)}.
     *
     * @param fragment The fragment to be shown.
     */
    public void hideFragment(Fragment fragment) {
        if (DEBUG) Log.v(TAG, "hide: " + fragment);
        if (!fragment.mHidden) {
            fragment.mHidden = true;
            // Toggle hidden changed so that if a fragment goes through show/hide/show
            // it doesn't go through the animation.
            fragment.mHiddenChanged = !fragment.mHiddenChanged;
        }
    }

    
Marks a fragment as shown to be later animated in with completeShowHideFragment(Fragment). 
Params:
fragment – The fragment to be shown./**
     * Marks a fragment as shown to be later animated in with
     * {@link #completeShowHideFragment(Fragment)}.
     *
     * @param fragment The fragment to be shown.
     */
    public void showFragment(Fragment fragment) {
        if (DEBUG) Log.v(TAG, "show: " + fragment);
        if (fragment.mHidden) {
            fragment.mHidden = false;
            // Toggle hidden changed so that if a fragment goes through show/hide/show
            // it doesn't go through the animation.
            fragment.mHiddenChanged = !fragment.mHiddenChanged;
        }
    }

    public void detachFragment(Fragment fragment) {
        if (DEBUG) Log.v(TAG, "detach: " + fragment);
        if (!fragment.mDetached) {
            fragment.mDetached = true;
            if (fragment.mAdded) {
                // We are not already in back stack, so need to remove the fragment.
                if (DEBUG) Log.v(TAG, "remove from detach: " + fragment);
                synchronized (mAdded) {
                    mAdded.remove(fragment);
                }
                if (fragment.mHasMenu && fragment.mMenuVisible) {
                    mNeedMenuInvalidate = true;
                }
                fragment.mAdded = false;
            }
        }
    }

    public void attachFragment(Fragment fragment) {
        if (DEBUG) Log.v(TAG, "attach: " + fragment);
        if (fragment.mDetached) {
            fragment.mDetached = false;
            if (!fragment.mAdded) {
                if (mAdded.contains(fragment)) {
                    throw new IllegalStateException("Fragment already added: " + fragment);
                }
                if (DEBUG) Log.v(TAG, "add from attach: " + fragment);
                synchronized (mAdded) {
                    mAdded.add(fragment);
                }
                fragment.mAdded = true;
                if (fragment.mHasMenu && fragment.mMenuVisible) {
                    mNeedMenuInvalidate = true;
                }
            }
        }
    }

    public Fragment findFragmentById(int id) {
        // First look through added fragments.
        for (int i = mAdded.size() - 1; i >= 0; i--) {
            Fragment f = mAdded.get(i);
            if (f != null && f.mFragmentId == id) {
                return f;
            }
        }
        if (mActive != null) {
            // Now for any known fragment.
            for (int i=mActive.size()-1; i>=0; i--) {
                Fragment f = mActive.valueAt(i);
                if (f != null && f.mFragmentId == id) {
                    return f;
                }
            }
        }
        return null;
    }
    
    public Fragment findFragmentByTag(String tag) {
        if (tag != null) {
            // First look through added fragments.
            for (int i=mAdded.size()-1; i>=0; i--) {
                Fragment f = mAdded.get(i);
                if (f != null && tag.equals(f.mTag)) {
                    return f;
                }
            }
        }
        if (mActive != null && tag != null) {
            // Now for any known fragment.
            for (int i=mActive.size()-1; i>=0; i--) {
                Fragment f = mActive.valueAt(i);
                if (f != null && tag.equals(f.mTag)) {
                    return f;
                }
            }
        }
        return null;
    }

    public Fragment findFragmentByWho(String who) {
        if (mActive != null && who != null) {
            for (int i=mActive.size()-1; i>=0; i--) {
                Fragment f = mActive.valueAt(i);
                if (f != null && (f=f.findFragmentByWho(who)) != null) {
                    return f;
                }
            }
        }
        return null;
    }
    
    private void checkStateLoss() {
        if (mStateSaved) {
            throw new IllegalStateException(
                    "Can not perform this action after onSaveInstanceState");
        }
        if (mNoTransactionsBecause != null) {
            throw new IllegalStateException(
                    "Can not perform this action inside of " + mNoTransactionsBecause);
        }
    }

    @Override
    public boolean isStateSaved() {
        return mStateSaved;
    }

    
Adds an action to the queue of pending actions.
Params:
action – the action to add
allowStateLoss – whether to allow loss of state information
Throws:
IllegalStateException – if the activity has been destroyed/**
     * Adds an action to the queue of pending actions.
     *
     * @param action the action to add
     * @param allowStateLoss whether to allow loss of state information
     * @throws IllegalStateException if the activity has been destroyed
     */
    public void enqueueAction(OpGenerator action, boolean allowStateLoss) {
        if (!allowStateLoss) {
            checkStateLoss();
        }
        synchronized (this) {
            if (mDestroyed || mHost == null) {
                if (allowStateLoss) {
                    // This FragmentManager isn't attached, so drop the entire transaction.
                    return;
                }
                throw new IllegalStateException("Activity has been destroyed");
            }
            if (mPendingActions == null) {
                mPendingActions = new ArrayList<>();
            }
            mPendingActions.add(action);
            scheduleCommit();
        }
    }

    
Schedules the execution when one hasn't been scheduled already. This should happen the first time enqueueAction(OpGenerator, boolean) is called or when a postponed transaction has been started with Fragment.startPostponedEnterTransition() /**
     * Schedules the execution when one hasn't been scheduled already. This should happen
     * the first time {@link #enqueueAction(OpGenerator, boolean)} is called or when
     * a postponed transaction has been started with
     * {@link Fragment#startPostponedEnterTransition()}
     */
    private void scheduleCommit() {
        synchronized (this) {
            boolean postponeReady =
                    mPostponedTransactions != null && !mPostponedTransactions.isEmpty();
            boolean pendingReady = mPendingActions != null && mPendingActions.size() == 1;
            if (postponeReady || pendingReady) {
                mHost.getHandler().removeCallbacks(mExecCommit);
                mHost.getHandler().post(mExecCommit);
            }
        }
    }
    
    public int allocBackStackIndex(BackStackRecord bse) {
        synchronized (this) {
            if (mAvailBackStackIndices == null || mAvailBackStackIndices.size() <= 0) {
                if (mBackStackIndices == null) {
                    mBackStackIndices = new ArrayList<BackStackRecord>();
                }
                int index = mBackStackIndices.size();
                if (DEBUG) Log.v(TAG, "Setting back stack index " + index + " to " + bse);
                mBackStackIndices.add(bse);
                return index;

            } else {
                int index = mAvailBackStackIndices.remove(mAvailBackStackIndices.size()-1);
                if (DEBUG) Log.v(TAG, "Adding back stack index " + index + " with " + bse);
                mBackStackIndices.set(index, bse);
                return index;
            }
        }
    }

    public void setBackStackIndex(int index, BackStackRecord bse) {
        synchronized (this) {
            if (mBackStackIndices == null) {
                mBackStackIndices = new ArrayList<BackStackRecord>();
            }
            int N = mBackStackIndices.size();
            if (index < N) {
                if (DEBUG) Log.v(TAG, "Setting back stack index " + index + " to " + bse);
                mBackStackIndices.set(index, bse);
            } else {
                while (N < index) {
                    mBackStackIndices.add(null);
                    if (mAvailBackStackIndices == null) {
                        mAvailBackStackIndices = new ArrayList<Integer>();
                    }
                    if (DEBUG) Log.v(TAG, "Adding available back stack index " + N);
                    mAvailBackStackIndices.add(N);
                    N++;
                }
                if (DEBUG) Log.v(TAG, "Adding back stack index " + index + " with " + bse);
                mBackStackIndices.add(bse);
            }
        }
    }

    public void freeBackStackIndex(int index) {
        synchronized (this) {
            mBackStackIndices.set(index, null);
            if (mAvailBackStackIndices == null) {
                mAvailBackStackIndices = new ArrayList<Integer>();
            }
            if (DEBUG) Log.v(TAG, "Freeing back stack index " + index);
            mAvailBackStackIndices.add(index);
        }
    }

    
Broken out from exec*, this prepares for gathering and executing operations.
Params:
allowStateLoss – true if state loss should be ignored or false if it should be
                      checked./**
     * Broken out from exec*, this prepares for gathering and executing operations.
     *
     * @param allowStateLoss true if state loss should be ignored or false if it should be
     *                       checked.
     */
    private void ensureExecReady(boolean allowStateLoss) {
        if (mExecutingActions) {
            throw new IllegalStateException("FragmentManager is already executing transactions");
        }

        if (Looper.myLooper() != mHost.getHandler().getLooper()) {
            throw new IllegalStateException("Must be called from main thread of fragment host");
        }

        if (!allowStateLoss) {
            checkStateLoss();
        }

        if (mTmpRecords == null) {
            mTmpRecords = new ArrayList<>();
            mTmpIsPop = new ArrayList<>();
        }
        mExecutingActions = true;
        try {
            executePostponedTransaction(null, null);
        } finally {
            mExecutingActions = false;
        }
    }

    public void execSingleAction(OpGenerator action, boolean allowStateLoss) {
        if (allowStateLoss && (mHost == null || mDestroyed)) {
            // This FragmentManager isn't attached, so drop the entire transaction.
            return;
        }
        ensureExecReady(allowStateLoss);
        if (action.generateOps(mTmpRecords, mTmpIsPop)) {
            mExecutingActions = true;
            try {
                removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop);
            } finally {
                cleanupExec();
            }
        }

        doPendingDeferredStart();
        burpActive();
    }

    
Broken out of exec*, this cleans up the mExecutingActions and the temporary structures
used in executing operations.
/**
     * Broken out of exec*, this cleans up the mExecutingActions and the temporary structures
     * used in executing operations.
     */
    private void cleanupExec() {
        mExecutingActions = false;
        mTmpIsPop.clear();
        mTmpRecords.clear();
    }

    
Only call from main thread!
/**
     * Only call from main thread!
     */
    public boolean execPendingActions() {
        ensureExecReady(true);

        boolean didSomething = false;
        while (generateOpsForPendingActions(mTmpRecords, mTmpIsPop)) {
            mExecutingActions = true;
            try {
                removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop);
            } finally {
                cleanupExec();
            }
            didSomething = true;
        }

        doPendingDeferredStart();
        burpActive();

        return didSomething;
    }

    
Complete the execution of transactions that have previously been postponed, but are
now ready.
/**
     * Complete the execution of transactions that have previously been postponed, but are
     * now ready.
     */
    private void executePostponedTransaction(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isRecordPop) {
        int numPostponed = mPostponedTransactions == null ? 0 : mPostponedTransactions.size();
        for (int i = 0; i < numPostponed; i++) {
            StartEnterTransitionListener listener = mPostponedTransactions.get(i);
            if (records != null && !listener.mIsBack) {
                int index = records.indexOf(listener.mRecord);
                if (index != -1 && isRecordPop.get(index)) {
                    listener.cancelTransaction();
                    continue;
                }
            }
            if (listener.isReady() || (records != null &&
                    listener.mRecord.interactsWith(records, 0, records.size()))) {
                mPostponedTransactions.remove(i);
                i--;
                numPostponed--;
                int index;
                if (records != null && !listener.mIsBack &&
                        (index = records.indexOf(listener.mRecord)) != -1 &&
                        isRecordPop.get(index)) {
                    // This is popping a postponed transaction
                    listener.cancelTransaction();
                } else {
                    listener.completeTransaction();
                }
            }
        }
    }

    
Remove redundant BackStackRecord operations and executes them. This method merges operations of proximate records that allow reordering. See FragmentTransaction.setReorderingAllowed(boolean). 

For example, a transaction that adds to the back stack and then another that pops that
back stack record will be optimized to remove the unnecessary operation.

Likewise, two transactions committed that are executed at the same time will be optimized
to remove the redundant operations as well as two pop operations executed together.
Params:
records – The records pending execution
isRecordPop – The direction that these records are being run./**
     * Remove redundant BackStackRecord operations and executes them. This method merges operations
     * of proximate records that allow reordering. See
     * {@link FragmentTransaction#setReorderingAllowed(boolean)}.
     * <p>
     * For example, a transaction that adds to the back stack and then another that pops that
     * back stack record will be optimized to remove the unnecessary operation.
     * <p>
     * Likewise, two transactions committed that are executed at the same time will be optimized
     * to remove the redundant operations as well as two pop operations executed together.
     *
     * @param records The records pending execution
     * @param isRecordPop The direction that these records are being run.
     */
    private void removeRedundantOperationsAndExecute(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isRecordPop) {
        if (records == null || records.isEmpty()) {
            return;
        }

        if (isRecordPop == null || records.size() != isRecordPop.size()) {
            throw new IllegalStateException("Internal error with the back stack records");
        }

        // Force start of any postponed transactions that interact with scheduled transactions:
        executePostponedTransaction(records, isRecordPop);

        final int numRecords = records.size();
        int startIndex = 0;
        for (int recordNum = 0; recordNum < numRecords; recordNum++) {
            final boolean canReorder = records.get(recordNum).mReorderingAllowed;
            if (!canReorder) {
                // execute all previous transactions
                if (startIndex != recordNum) {
                    executeOpsTogether(records, isRecordPop, startIndex, recordNum);
                }
                // execute all pop operations that don't allow reordering together or
                // one add operation
                int reorderingEnd = recordNum + 1;
                if (isRecordPop.get(recordNum)) {
                    while (reorderingEnd < numRecords
                            && isRecordPop.get(reorderingEnd)
                            && !records.get(reorderingEnd).mReorderingAllowed) {
                        reorderingEnd++;
                    }
                }
                executeOpsTogether(records, isRecordPop, recordNum, reorderingEnd);
                startIndex = reorderingEnd;
                recordNum = reorderingEnd - 1;
            }
        }
        if (startIndex != numRecords) {
            executeOpsTogether(records, isRecordPop, startIndex, numRecords);
        }
    }

    
Executes a subset of a list of BackStackRecords, all of which either allow reordering or
do not allow ordering.
Params:
records – A list of BackStackRecords that are to be executed together
isRecordPop – The direction that these records are being run.
startIndex – The index of the first record in records to be executed
endIndex – One more than the final record index in records to executed./**
     * Executes a subset of a list of BackStackRecords, all of which either allow reordering or
     * do not allow ordering.
     * @param records A list of BackStackRecords that are to be executed together
     * @param isRecordPop The direction that these records are being run.
     * @param startIndex The index of the first record in <code>records</code> to be executed
     * @param endIndex One more than the final record index in <code>records</code> to executed.
     */
    private void executeOpsTogether(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
        final boolean allowReordering = records.get(startIndex).mReorderingAllowed;
        boolean addToBackStack = false;
        if (mTmpAddedFragments == null) {
            mTmpAddedFragments = new ArrayList<>();
        } else {
            mTmpAddedFragments.clear();
        }
        mTmpAddedFragments.addAll(mAdded);
        Fragment oldPrimaryNav = getPrimaryNavigationFragment();
        for (int recordNum = startIndex; recordNum < endIndex; recordNum++) {
            final BackStackRecord record = records.get(recordNum);
            final boolean isPop = isRecordPop.get(recordNum);
            if (!isPop) {
                oldPrimaryNav = record.expandOps(mTmpAddedFragments, oldPrimaryNav);
            } else {
                record.trackAddedFragmentsInPop(mTmpAddedFragments);
            }
            addToBackStack = addToBackStack || record.mAddToBackStack;
        }
        mTmpAddedFragments.clear();

        if (!allowReordering) {
            FragmentTransition.startTransitions(this, records, isRecordPop, startIndex, endIndex,
                    false);
        }
        executeOps(records, isRecordPop, startIndex, endIndex);

        int postponeIndex = endIndex;
        if (allowReordering) {
            ArraySet<Fragment> addedFragments = new ArraySet<>();
            addAddedFragments(addedFragments);
            postponeIndex = postponePostponableTransactions(records, isRecordPop,
                    startIndex, endIndex, addedFragments);
            makeRemovedFragmentsInvisible(addedFragments);
        }

        if (postponeIndex != startIndex && allowReordering) {
            // need to run something now
            FragmentTransition.startTransitions(this, records, isRecordPop, startIndex,
                    postponeIndex, true);
            moveToState(mCurState, true);
        }

        for (int recordNum = startIndex; recordNum < endIndex; recordNum++) {
            final BackStackRecord record = records.get(recordNum);
            final boolean isPop = isRecordPop.get(recordNum);
            if (isPop && record.mIndex >= 0) {
                freeBackStackIndex(record.mIndex);
                record.mIndex = -1;
            }
            record.runOnCommitRunnables();
        }

        if (addToBackStack) {
            reportBackStackChanged();
        }
    }

    
Any fragments that were removed because they have been postponed should have their views
made invisible by setting their transition alpha to 0.
Params:
fragments – The fragments that were added during operation execution. Only the ones
                 that are no longer added will have their transition alpha changed./**
     * Any fragments that were removed because they have been postponed should have their views
     * made invisible by setting their transition alpha to 0.
     *
     * @param fragments The fragments that were added during operation execution. Only the ones
     *                  that are no longer added will have their transition alpha changed.
     */
    private void makeRemovedFragmentsInvisible(ArraySet<Fragment> fragments) {
        final int numAdded = fragments.size();
        for (int i = 0; i < numAdded; i++) {
            final Fragment fragment = fragments.valueAt(i);
            if (!fragment.mAdded) {
                final View view = fragment.getView();
                view.setTransitionAlpha(0f);
            }
        }
    }

    
Examine all transactions and determine which ones are marked as postponed. Those will
have their operations rolled back and moved to the end of the record list (up to endIndex).
It will also add the postponed transaction to the queue.
Params:
records – A list of BackStackRecords that should be checked.
isRecordPop – The direction that these records are being run.
startIndex – The index of the first record in records to be checked
endIndex – One more than the final record index in records to be checked.
Returns:
The index of the first postponed transaction or endIndex if no transaction was
postponed./**
     * Examine all transactions and determine which ones are marked as postponed. Those will
     * have their operations rolled back and moved to the end of the record list (up to endIndex).
     * It will also add the postponed transaction to the queue.
     *
     * @param records A list of BackStackRecords that should be checked.
     * @param isRecordPop The direction that these records are being run.
     * @param startIndex The index of the first record in <code>records</code> to be checked
     * @param endIndex One more than the final record index in <code>records</code> to be checked.
     * @return The index of the first postponed transaction or endIndex if no transaction was
     * postponed.
     */
    private int postponePostponableTransactions(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isRecordPop, int startIndex, int endIndex,
            ArraySet<Fragment> added) {
        int postponeIndex = endIndex;
        for (int i = endIndex - 1; i >= startIndex; i--) {
            final BackStackRecord record = records.get(i);
            final boolean isPop = isRecordPop.get(i);
            boolean isPostponed = record.isPostponed() &&
                    !record.interactsWith(records, i + 1, endIndex);
            if (isPostponed) {
                if (mPostponedTransactions == null) {
                    mPostponedTransactions = new ArrayList<>();
                }
                StartEnterTransitionListener listener =
                        new StartEnterTransitionListener(record, isPop);
                mPostponedTransactions.add(listener);
                record.setOnStartPostponedListener(listener);

                // roll back the transaction
                if (isPop) {
                    record.executeOps();
                } else {
                    record.executePopOps(false);
                }

                // move to the end
                postponeIndex--;
                if (i != postponeIndex) {
                    records.remove(i);
                    records.add(postponeIndex, record);
                }

                // different views may be visible now
                addAddedFragments(added);
            }
        }
        return postponeIndex;
    }

    
When a postponed transaction is ready to be started, this completes the transaction,
removing, hiding, or showing views as well as starting the animations and transitions.
 runtransitions is set to false when the transaction postponement was interrupted abnormally -- normally by a new transaction being started that affects the postponed transaction. 
Params:
record – The transaction to run
isPop – true if record is popping or false if it is adding
runTransitions – true if the fragment transition should be run or false otherwise.
moveToState – true if the state should be changed after executing the operations.
                   This is false when the transaction is canceled when a postponed
                   transaction is popped./**
     * When a postponed transaction is ready to be started, this completes the transaction,
     * removing, hiding, or showing views as well as starting the animations and transitions.
     * <p>
     * {@code runtransitions} is set to false when the transaction postponement was interrupted
     * abnormally -- normally by a new transaction being started that affects the postponed
     * transaction.
     *
     * @param record The transaction to run
     * @param isPop true if record is popping or false if it is adding
     * @param runTransitions true if the fragment transition should be run or false otherwise.
     * @param moveToState true if the state should be changed after executing the operations.
     *                    This is false when the transaction is canceled when a postponed
     *                    transaction is popped.
     */
    private void completeExecute(BackStackRecord record, boolean isPop, boolean runTransitions,
            boolean moveToState) {
        if (isPop) {
            record.executePopOps(moveToState);
        } else {
            record.executeOps();
        }
        ArrayList<BackStackRecord> records = new ArrayList<>(1);
        ArrayList<Boolean> isRecordPop = new ArrayList<>(1);
        records.add(record);
        isRecordPop.add(isPop);
        if (runTransitions) {
            FragmentTransition.startTransitions(this, records, isRecordPop, 0, 1, true);
        }
        if (moveToState) {
            moveToState(mCurState, true);
        }

        if (mActive != null) {
            final int numActive = mActive.size();
            for (int i = 0; i < numActive; i++) {
                // Allow added fragments to be removed during the pop since we aren't going
                // to move them to the final state with moveToState(mCurState).
                Fragment fragment = mActive.valueAt(i);
                if (fragment != null && fragment.mView != null && fragment.mIsNewlyAdded
                        && record.interactsWith(fragment.mContainerId)) {
                    fragment.mIsNewlyAdded = false;
                }
            }
        }
    }

    
Find a fragment within the fragment's container whose View should be below the passed fragment. null is returned when the fragment has no View or if there should be no fragment with a View below the given fragment. As an example, if mAdded has two Fragments with Views sharing the same container: FragmentA FragmentB Then, when processing FragmentB, FragmentA will be returned. If, however, FragmentA had no View, null would be returned. 
Params:
f – The fragment that may be on top of another fragment.
Returns:
The fragment with a View under f, if one exists or null if f has no View or
there are no fragments with Views in the same container./**
     * Find a fragment within the fragment's container whose View should be below the passed
     * fragment. {@code null} is returned when the fragment has no View or if there should be
     * no fragment with a View below the given fragment.
     *
     * As an example, if mAdded has two Fragments with Views sharing the same container:
     * FragmentA
     * FragmentB
     *
     * Then, when processing FragmentB, FragmentA will be returned. If, however, FragmentA
     * had no View, null would be returned.
     *
     * @param f The fragment that may be on top of another fragment.
     * @return The fragment with a View under f, if one exists or null if f has no View or
     * there are no fragments with Views in the same container.
     */
    private Fragment findFragmentUnder(Fragment f) {
        final ViewGroup container = f.mContainer;
        final View view = f.mView;

        if (container == null || view == null) {
            return null;
        }

        final int fragmentIndex = mAdded.indexOf(f);
        for (int i = fragmentIndex - 1; i >= 0; i--) {
            Fragment underFragment = mAdded.get(i);
            if (underFragment.mContainer == container && underFragment.mView != null) {
                // Found the fragment under this one
                return underFragment;
            }
        }
        return null;
    }

    
Run the operations in the BackStackRecords, either to push or pop.
Params:
records – The list of records whose operations should be run.
isRecordPop – The direction that these records are being run.
startIndex – The index of the first entry in records to run.
endIndex – One past the index of the final entry in records to run./**
     * Run the operations in the BackStackRecords, either to push or pop.
     *
     * @param records The list of records whose operations should be run.
     * @param isRecordPop The direction that these records are being run.
     * @param startIndex The index of the first entry in records to run.
     * @param endIndex One past the index of the final entry in records to run.
     */
    private static void executeOps(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
        for (int i = startIndex; i < endIndex; i++) {
            final BackStackRecord record = records.get(i);
            final boolean isPop = isRecordPop.get(i);
            if (isPop) {
                record.bumpBackStackNesting(-1);
                // Only execute the add operations at the end of
                // all transactions.
                boolean moveToState = i == (endIndex - 1);
                record.executePopOps(moveToState);
            } else {
                record.bumpBackStackNesting(1);
                record.executeOps();
            }
        }
    }

    
Ensure that fragments that are added are moved to at least the CREATED state. Any newly-added Views are inserted into added so that the Transaction can be postponed with Fragment.postponeEnterTransition(). They will later be made invisible by changing their transitionAlpha to 0 if they have been removed when postponed. /**
     * Ensure that fragments that are added are moved to at least the CREATED state.
     * Any newly-added Views are inserted into {@code added} so that the Transaction can be
     * postponed with {@link Fragment#postponeEnterTransition()}. They will later be made
     * invisible by changing their transitionAlpha to 0 if they have been removed when postponed.
     */
    private void addAddedFragments(ArraySet<Fragment> added) {
        if (mCurState < Fragment.CREATED) {
            return;
        }
        // We want to leave the fragment in the started state
        final int state = Math.min(mCurState, Fragment.STARTED);
        final int numAdded = mAdded.size();
        for (int i = 0; i < numAdded; i++) {
            Fragment fragment = mAdded.get(i);
            if (fragment.mState < state) {
                moveToState(fragment, state, fragment.getNextAnim(), fragment.getNextTransition(), false);
                if (fragment.mView != null && !fragment.mHidden && fragment.mIsNewlyAdded) {
                    added.add(fragment);
                }
            }
        }
    }

    
Starts all postponed transactions regardless of whether they are ready or not.
/**
     * Starts all postponed transactions regardless of whether they are ready or not.
     */
    private void forcePostponedTransactions() {
        if (mPostponedTransactions != null) {
            while (!mPostponedTransactions.isEmpty()) {
                mPostponedTransactions.remove(0).completeTransaction();
            }
        }
    }

    
Ends the animations of fragments so that they immediately reach the end state.
This is used prior to saving the state so that the correct state is saved.
/**
     * Ends the animations of fragments so that they immediately reach the end state.
     * This is used prior to saving the state so that the correct state is saved.
     */
    private void endAnimatingAwayFragments() {
        final int numFragments = mActive == null ? 0 : mActive.size();
        for (int i = 0; i < numFragments; i++) {
            Fragment fragment = mActive.valueAt(i);
            if (fragment != null && fragment.getAnimatingAway() != null) {
                // Give up waiting for the animation and just end it.
                fragment.getAnimatingAway().end();
            }
        }
    }

    
Adds all records in the pending actions to records and whether they are add or pop
operations to isPop. After executing, the pending actions will be empty.
Params:
records – All pending actions will generate BackStackRecords added to this.
               This contains the transactions, in order, to execute.
isPop – All pending actions will generate booleans to add to this. This contains
             an entry for each entry in records to indicate whether or not it is a
             pop action./**
     * Adds all records in the pending actions to records and whether they are add or pop
     * operations to isPop. After executing, the pending actions will be empty.
     *
     * @param records All pending actions will generate BackStackRecords added to this.
     *                This contains the transactions, in order, to execute.
     * @param isPop All pending actions will generate booleans to add to this. This contains
     *              an entry for each entry in records to indicate whether or not it is a
     *              pop action.
     */
    private boolean generateOpsForPendingActions(ArrayList<BackStackRecord> records,
            ArrayList<Boolean> isPop) {
        boolean didSomething = false;
        synchronized (this) {
            if (mPendingActions == null || mPendingActions.size() == 0) {
                return false;
            }

            final int numActions = mPendingActions.size();
            for (int i = 0; i < numActions; i++) {
                didSomething |= mPendingActions.get(i).generateOps(records, isPop);
            }
            mPendingActions.clear();
            mHost.getHandler().removeCallbacks(mExecCommit);
        }
        return didSomething;
    }

    void doPendingDeferredStart() {
        if (mHavePendingDeferredStart) {
            boolean loadersRunning = false;
            for (int i=0; i<mActive.size(); i++) {
                Fragment f = mActive.valueAt(i);
                if (f != null && f.mLoaderManager != null) {
                    loadersRunning |= f.mLoaderManager.hasRunningLoaders();
                }
            }
            if (!loadersRunning) {
                mHavePendingDeferredStart = false;
                startPendingDeferredFragments();
            }
        }
    }

    void reportBackStackChanged() {
        if (mBackStackChangeListeners != null) {
            for (int i=0; i<mBackStackChangeListeners.size(); i++) {
                mBackStackChangeListeners.get(i).onBackStackChanged();
            }
        }
    }

    void addBackStackState(BackStackRecord state) {
        if (mBackStack == null) {
            mBackStack = new ArrayList<BackStackRecord>();
        }
        mBackStack.add(state);
    }

    boolean popBackStackState(ArrayList<BackStackRecord> records, ArrayList<Boolean> isRecordPop,
            String name, int id, int flags) {
        if (mBackStack == null) {
            return false;
        }
        if (name == null && id < 0 && (flags & POP_BACK_STACK_INCLUSIVE) == 0) {
            int last = mBackStack.size() - 1;
            if (last < 0) {
                return false;
            }
            records.add(mBackStack.remove(last));
            isRecordPop.add(true);
        } else {
            int index = -1;
            if (name != null || id >= 0) {
                // If a name or ID is specified, look for that place in
                // the stack.
                index = mBackStack.size()-1;
                while (index >= 0) {
                    BackStackRecord bss = mBackStack.get(index);
                    if (name != null && name.equals(bss.getName())) {
                        break;
                    }
                    if (id >= 0 && id == bss.mIndex) {
                        break;
                    }
                    index--;
                }
                if (index < 0) {
                    return false;
                }
                if ((flags&POP_BACK_STACK_INCLUSIVE) != 0) {
                    index--;
                    // Consume all following entries that match.
                    while (index >= 0) {
                        BackStackRecord bss = mBackStack.get(index);
                        if ((name != null && name.equals(bss.getName()))
                                || (id >= 0 && id == bss.mIndex)) {
                            index--;
                            continue;
                        }
                        break;
                    }
                }
            }
            if (index == mBackStack.size()-1) {
                return false;
            }
            for (int i = mBackStack.size() - 1; i > index; i--) {
                records.add(mBackStack.remove(i));
                isRecordPop.add(true);
            }
        }
        return true;
    }

    FragmentManagerNonConfig retainNonConfig() {
        setRetaining(mSavedNonConfig);
        return mSavedNonConfig;
    }

    
Recurse the FragmentManagerNonConfig fragments and set the mRetaining to true. This was previously done while saving the non-config state, but that has been moved to saveNonConfig() called from saveAllState(). If mRetaining is set too early, the fragment won't be destroyed when the FragmentManager is destroyed. /**
     * Recurse the FragmentManagerNonConfig fragments and set the mRetaining to true. This
     * was previously done while saving the non-config state, but that has been moved to
     * {@link #saveNonConfig()} called from {@link #saveAllState()}. If mRetaining is set too
     * early, the fragment won't be destroyed when the FragmentManager is destroyed.
     */
    private static void setRetaining(FragmentManagerNonConfig nonConfig) {
        if (nonConfig == null) {
            return;
        }
        List<Fragment> fragments = nonConfig.getFragments();
        if (fragments != null) {
            for (Fragment fragment : fragments) {
                fragment.mRetaining = true;
            }
        }
        List<FragmentManagerNonConfig> children = nonConfig.getChildNonConfigs();
        if (children != null) {
            for (FragmentManagerNonConfig child : children) {
                setRetaining(child);
            }
        }
    }

    void saveNonConfig() {
        ArrayList<Fragment> fragments = null;
        ArrayList<FragmentManagerNonConfig> childFragments = null;
        if (mActive != null) {
            for (int i=0; i<mActive.size(); i++) {
                Fragment f = mActive.valueAt(i);
                if (f != null) {
                    if (f.mRetainInstance) {
                        if (fragments == null) {
                            fragments = new ArrayList<>();
                        }
                        fragments.add(f);
                        f.mTargetIndex = f.mTarget != null ? f.mTarget.mIndex : -1;
                        if (DEBUG) Log.v(TAG, "retainNonConfig: keeping retained " + f);
                    }
                    FragmentManagerNonConfig child;
                    if (f.mChildFragmentManager != null) {
                        f.mChildFragmentManager.saveNonConfig();
                        child = f.mChildFragmentManager.mSavedNonConfig;
                    } else {
                        // f.mChildNonConfig may be not null, when the parent fragment is
                        // in the backstack.
                        child = f.mChildNonConfig;
                    }

                    if (childFragments == null && child != null) {
                        childFragments = new ArrayList<>(mActive.size());
                        for (int j = 0; j < i; j++) {
                            childFragments.add(null);
                        }
                    }

                    if (childFragments != null) {
                        childFragments.add(child);
                    }
                }
            }
        }
        if (fragments == null && childFragments == null) {
            mSavedNonConfig = null;
        } else {
            mSavedNonConfig = new FragmentManagerNonConfig(fragments, childFragments);
        }
    }
    
    void saveFragmentViewState(Fragment f) {
        if (f.mView == null) {
            return;
        }
        if (mStateArray == null) {
            mStateArray = new SparseArray<Parcelable>();
        } else {
            mStateArray.clear();
        }
        f.mView.saveHierarchyState(mStateArray);
        if (mStateArray.size() > 0) {
            f.mSavedViewState = mStateArray;
            mStateArray = null;
        }
    }
    
    Bundle saveFragmentBasicState(Fragment f) {
        Bundle result = null;

        if (mStateBundle == null) {
            mStateBundle = new Bundle();
        }
        f.performSaveInstanceState(mStateBundle);
        dispatchOnFragmentSaveInstanceState(f, mStateBundle, false);
        if (!mStateBundle.isEmpty()) {
            result = mStateBundle;
            mStateBundle = null;
        }

        if (f.mView != null) {
            saveFragmentViewState(f);
        }
        if (f.mSavedViewState != null) {
            if (result == null) {
                result = new Bundle();
            }
            result.putSparseParcelableArray(
                    FragmentManagerImpl.VIEW_STATE_TAG, f.mSavedViewState);
        }
        if (!f.mUserVisibleHint) {
            if (result == null) {
                result = new Bundle();
            }
            // Only add this if it's not the default value
            result.putBoolean(FragmentManagerImpl.USER_VISIBLE_HINT_TAG, f.mUserVisibleHint);
        }

        return result;
    }

    Parcelable saveAllState() {
        // Make sure all pending operations have now been executed to get
        // our state update-to-date.
        forcePostponedTransactions();
        endAnimatingAwayFragments();
        execPendingActions();

        mStateSaved = true;
        mSavedNonConfig = null;

        if (mActive == null || mActive.size() <= 0) {
            return null;
        }
        
        // First collect all active fragments.
        int N = mActive.size();
        FragmentState[] active = new FragmentState[N];
        boolean haveFragments = false;
        for (int i=0; i<N; i++) {
            Fragment f = mActive.valueAt(i);
            if (f != null) {
                if (f.mIndex < 0) {
                    throwException(new IllegalStateException(
                            "Failure saving state: active " + f
                            + " has cleared index: " + f.mIndex));
                }

                haveFragments = true;

                FragmentState fs = new FragmentState(f);
                active[i] = fs;
                
                if (f.mState > Fragment.INITIALIZING && fs.mSavedFragmentState == null) {
                    fs.mSavedFragmentState = saveFragmentBasicState(f);

                    if (f.mTarget != null) {
                        if (f.mTarget.mIndex < 0) {
                            throwException(new IllegalStateException(
                                    "Failure saving state: " + f
                                    + " has target not in fragment manager: " + f.mTarget));
                        }
                        if (fs.mSavedFragmentState == null) {
                            fs.mSavedFragmentState = new Bundle();
                        }
                        putFragment(fs.mSavedFragmentState,
                                FragmentManagerImpl.TARGET_STATE_TAG, f.mTarget);
                        if (f.mTargetRequestCode != 0) {
                            fs.mSavedFragmentState.putInt(
                                    FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG,
                                    f.mTargetRequestCode);
                        }
                    }

                } else {
                    fs.mSavedFragmentState = f.mSavedFragmentState;
                }
                
                if (DEBUG) Log.v(TAG, "Saved state of " + f + ": "
                        + fs.mSavedFragmentState);
            }
        }
        
        if (!haveFragments) {
            if (DEBUG) Log.v(TAG, "saveAllState: no fragments!");
            return null;
        }
        
        int[] added = null;
        BackStackState[] backStack = null;
        
        // Build list of currently added fragments.
        N = mAdded.size();
        if (N > 0) {
            added = new int[N];
            for (int i=0; i<N; i++) {
                added[i] = mAdded.get(i).mIndex;
                if (added[i] < 0) {
                    throwException(new IllegalStateException(
                            "Failure saving state: active " + mAdded.get(i)
                            + " has cleared index: " + added[i]));
                }
                if (DEBUG) Log.v(TAG, "saveAllState: adding fragment #" + i
                        + ": " + mAdded.get(i));
            }
        }

        // Now save back stack.
        if (mBackStack != null) {
            N = mBackStack.size();
            if (N > 0) {
                backStack = new BackStackState[N];
                for (int i=0; i<N; i++) {
                    backStack[i] = new BackStackState(this, mBackStack.get(i));
                    if (DEBUG) Log.v(TAG, "saveAllState: adding back stack #" + i
                            + ": " + mBackStack.get(i));
                }
            }
        }
        
        FragmentManagerState fms = new FragmentManagerState();
        fms.mActive = active;
        fms.mAdded = added;
        fms.mBackStack = backStack;
        fms.mNextFragmentIndex = mNextFragmentIndex;
        if (mPrimaryNav != null) {
            fms.mPrimaryNavActiveIndex = mPrimaryNav.mIndex;
        }
        saveNonConfig();
        return fms;
    }
    
    void restoreAllState(Parcelable state, FragmentManagerNonConfig nonConfig) {
        // If there is no saved state at all, then there can not be
        // any nonConfig fragments either, so that is that.
        if (state == null) return;
        FragmentManagerState fms = (FragmentManagerState)state;
        if (fms.mActive == null) return;

        List<FragmentManagerNonConfig> childNonConfigs = null;

        // First re-attach any non-config instances we are retaining back
        // to their saved state, so we don't try to instantiate them again.
        if (nonConfig != null) {
            List<Fragment> nonConfigFragments = nonConfig.getFragments();
            childNonConfigs = nonConfig.getChildNonConfigs();
            final int count = nonConfigFragments != null ? nonConfigFragments.size() : 0;
            for (int i = 0; i < count; i++) {
                Fragment f = nonConfigFragments.get(i);
                if (DEBUG) Log.v(TAG, "restoreAllState: re-attaching retained " + f);
                int index = 0; // index of f in fms.mActive
                while (index < fms.mActive.length && fms.mActive[index].mIndex != f.mIndex) {
                    index++;
                }
                if (index == fms.mActive.length) {
                    throwException(new IllegalStateException("Could not find active fragment "
                            + "with index " + f.mIndex));
                }
                FragmentState fs = fms.mActive[index];
                fs.mInstance = f;
                f.mSavedViewState = null;
                f.mBackStackNesting = 0;
                f.mInLayout = false;
                f.mAdded = false;
                f.mTarget = null;
                if (fs.mSavedFragmentState != null) {
                    fs.mSavedFragmentState.setClassLoader(mHost.getContext().getClassLoader());
                    f.mSavedViewState = fs.mSavedFragmentState.getSparseParcelableArray(
                            FragmentManagerImpl.VIEW_STATE_TAG);
                    f.mSavedFragmentState = fs.mSavedFragmentState;
                }
            }
        }
        
        // Build the full list of active fragments, instantiating them from
        // their saved state.
        mActive = new SparseArray<>(fms.mActive.length);
        for (int i=0; i<fms.mActive.length; i++) {
            FragmentState fs = fms.mActive[i];
            if (fs != null) {
                FragmentManagerNonConfig childNonConfig = null;
                if (childNonConfigs != null && i < childNonConfigs.size()) {
                    childNonConfig = childNonConfigs.get(i);
                }
                Fragment f = fs.instantiate(mHost, mContainer, mParent, childNonConfig);
                if (DEBUG) Log.v(TAG, "restoreAllState: active #" + i + ": " + f);
                mActive.put(f.mIndex, f);
                // Now that the fragment is instantiated (or came from being
                // retained above), clear mInstance in case we end up re-restoring
                // from this FragmentState again.
                fs.mInstance = null;
            }
        }
        
        // Update the target of all retained fragments.
        if (nonConfig != null) {
            List<Fragment> nonConfigFragments = nonConfig.getFragments();
            final int count = nonConfigFragments != null ? nonConfigFragments.size() : 0;
            for (int i = 0; i < count; i++) {
                Fragment f = nonConfigFragments.get(i);
                if (f.mTargetIndex >= 0) {
                    f.mTarget = mActive.get(f.mTargetIndex);
                    if (f.mTarget == null) {
                        Log.w(TAG, "Re-attaching retained fragment " + f
                                + " target no longer exists: " + f.mTargetIndex);
                        f.mTarget = null;
                    }
                }
            }
        }

        // Build the list of currently added fragments.
        mAdded.clear();
        if (fms.mAdded != null) {
            for (int i=0; i<fms.mAdded.length; i++) {
                Fragment f = mActive.get(fms.mAdded[i]);
                if (f == null) {
                    throwException(new IllegalStateException(
                            "No instantiated fragment for index #" + fms.mAdded[i]));
                }
                f.mAdded = true;
                if (DEBUG) Log.v(TAG, "restoreAllState: added #" + i + ": " + f);
                if (mAdded.contains(f)) {
                    throw new IllegalStateException("Already added!");
                }
                synchronized (mAdded) {
                    mAdded.add(f);
                }
            }
        }
        
        // Build the back stack.
        if (fms.mBackStack != null) {
            mBackStack = new ArrayList<BackStackRecord>(fms.mBackStack.length);
            for (int i=0; i<fms.mBackStack.length; i++) {
                BackStackRecord bse = fms.mBackStack[i].instantiate(this);
                if (DEBUG) {
                    Log.v(TAG, "restoreAllState: back stack #" + i
                        + " (index " + bse.mIndex + "): " + bse);
                    LogWriter logw = new LogWriter(Log.VERBOSE, TAG);
                    PrintWriter pw = new FastPrintWriter(logw, false, 1024);
                    bse.dump("  ", pw, false);
                    pw.flush();
                }
                mBackStack.add(bse);
                if (bse.mIndex >= 0) {
                    setBackStackIndex(bse.mIndex, bse);
                }
            }
        } else {
            mBackStack = null;
        }

        if (fms.mPrimaryNavActiveIndex >= 0) {
            mPrimaryNav = mActive.get(fms.mPrimaryNavActiveIndex);
        }

        mNextFragmentIndex = fms.mNextFragmentIndex;
    }

    
To prevent list modification errors, mActive sets values to null instead of
removing them when the Fragment becomes inactive. This cleans up the list at the
end of executing the transactions.
/**
     * To prevent list modification errors, mActive sets values to null instead of
     * removing them when the Fragment becomes inactive. This cleans up the list at the
     * end of executing the transactions.
     */
    private void burpActive() {
        if (mActive != null) {
            for (int i = mActive.size() - 1; i >= 0; i--) {
                if (mActive.valueAt(i) == null) {
                    mActive.delete(mActive.keyAt(i));
                }
            }
        }
    }

    public void attachController(FragmentHostCallback<?> host, FragmentContainer container,
            Fragment parent) {
        if (mHost != null) throw new IllegalStateException("Already attached");
        mHost = host;
        mContainer = container;
        mParent = parent;
        mAllowOldReentrantBehavior = getTargetSdk() <= Build.VERSION_CODES.N_MR1;
    }

    
Returns:
the target SDK of the FragmentManager's application info. If the
FragmentManager has been torn down, then 0 is returned./**
     * @return the target SDK of the FragmentManager's application info. If the
     * FragmentManager has been torn down, then 0 is returned.
     */
    int getTargetSdk() {
        if (mHost != null) {
            Context context = mHost.getContext();
            if (context != null) {
                ApplicationInfo info = context.getApplicationInfo();
                if (info != null) {
                    return info.targetSdkVersion;
                }
            }
        }
        return 0;
    }

    public void noteStateNotSaved() {
        mSavedNonConfig = null;
        mStateSaved = false;
        final int addedCount = mAdded.size();
        for (int i = 0; i < addedCount; i++) {
            Fragment fragment = mAdded.get(i);
            if (fragment != null) {
                fragment.noteStateNotSaved();
            }
        }
    }

    public void dispatchCreate() {
        mStateSaved = false;
        dispatchMoveToState(Fragment.CREATED);
    }
    
    public void dispatchActivityCreated() {
        mStateSaved = false;
        dispatchMoveToState(Fragment.ACTIVITY_CREATED);
    }
    
    public void dispatchStart() {
        mStateSaved = false;
        dispatchMoveToState(Fragment.STARTED);
    }
    
    public void dispatchResume() {
        mStateSaved = false;
        dispatchMoveToState(Fragment.RESUMED);
    }
    
    public void dispatchPause() {
        dispatchMoveToState(Fragment.STARTED);
    }
    
    public void dispatchStop() {
        dispatchMoveToState(Fragment.STOPPED);
    }
    
    public void dispatchDestroyView() {
        dispatchMoveToState(Fragment.CREATED);
    }

    public void dispatchDestroy() {
        mDestroyed = true;
        execPendingActions();
        dispatchMoveToState(Fragment.INITIALIZING);
        mHost = null;
        mContainer = null;
        mParent = null;
    }

    
This method is called by dispatch* methods to change the FragmentManager's state.
It calls moveToState directly if the target SDK is older than O. Otherwise, it sets and
clears mExecutingActions to ensure that there is no reentrancy while the
FragmentManager is changing state.
Params:
state – The new state of the FragmentManager./**
     * This method is called by dispatch* methods to change the FragmentManager's state.
     * It calls moveToState directly if the target SDK is older than O. Otherwise, it sets and
     * clears mExecutingActions to ensure that there is no reentrancy while the
     * FragmentManager is changing state.
     *
     * @param state The new state of the FragmentManager.
     */
    private void dispatchMoveToState(int state) {
        if (mAllowOldReentrantBehavior) {
            moveToState(state, false);
        } else {
            try {
                mExecutingActions = true;
                moveToState(state, false);
            } finally {
                mExecutingActions = false;
            }
        }
        execPendingActions();
    }

    
Deprecated:
use dispatchMultiWindowModeChanged(boolean, Configuration)/**
     * @deprecated use {@link #dispatchMultiWindowModeChanged(boolean, Configuration)}
     */
    @Deprecated
    public void dispatchMultiWindowModeChanged(boolean isInMultiWindowMode) {
        for (int i = mAdded.size() - 1; i >= 0; --i) {
            final Fragment f = mAdded.get(i);
            if (f != null) {
                f.performMultiWindowModeChanged(isInMultiWindowMode);
            }
        }
    }

    public void dispatchMultiWindowModeChanged(boolean isInMultiWindowMode,
            Configuration newConfig) {
        for (int i = mAdded.size() - 1; i >= 0; --i) {
            final Fragment f = mAdded.get(i);
            if (f != null) {
                f.performMultiWindowModeChanged(isInMultiWindowMode, newConfig);
            }
        }
    }

    
Deprecated:
use dispatchPictureInPictureModeChanged(boolean, Configuration)/**
     * @deprecated use {@link #dispatchPictureInPictureModeChanged(boolean, Configuration)}
     */
    @Deprecated
    public void dispatchPictureInPictureModeChanged(boolean isInPictureInPictureMode) {
        for (int i = mAdded.size() - 1; i >= 0; --i) {
            final Fragment f = mAdded.get(i);
            if (f != null) {
                f.performPictureInPictureModeChanged(isInPictureInPictureMode);
            }
        }
    }

    public void dispatchPictureInPictureModeChanged(boolean isInPictureInPictureMode,
            Configuration newConfig) {
        for (int i = mAdded.size() - 1; i >= 0; --i) {
            final Fragment f = mAdded.get(i);
            if (f != null) {
                f.performPictureInPictureModeChanged(isInPictureInPictureMode, newConfig);
            }
        }
    }

    public void dispatchConfigurationChanged(Configuration newConfig) {
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                f.performConfigurationChanged(newConfig);
            }
        }
    }

    public void dispatchLowMemory() {
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                f.performLowMemory();
            }
        }
    }

    public void dispatchTrimMemory(int level) {
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                f.performTrimMemory(level);
            }
        }
    }

    public boolean dispatchCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        if (mCurState < Fragment.CREATED) {
            return false;
        }
        boolean show = false;
        ArrayList<Fragment> newMenus = null;
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                if (f.performCreateOptionsMenu(menu, inflater)) {
                    show = true;
                    if (newMenus == null) {
                        newMenus = new ArrayList<Fragment>();
                    }
                    newMenus.add(f);
                }
            }
        }

        if (mCreatedMenus != null) {
            for (int i=0; i<mCreatedMenus.size(); i++) {
                Fragment f = mCreatedMenus.get(i);
                if (newMenus == null || !newMenus.contains(f)) {
                    f.onDestroyOptionsMenu();
                }
            }
        }
        
        mCreatedMenus = newMenus;
        
        return show;
    }
    
    public boolean dispatchPrepareOptionsMenu(Menu menu) {
        if (mCurState < Fragment.CREATED) {
            return false;
        }
        boolean show = false;
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                if (f.performPrepareOptionsMenu(menu)) {
                    show = true;
                }
            }
        }
        return show;
    }
    
    public boolean dispatchOptionsItemSelected(MenuItem item) {
        if (mCurState < Fragment.CREATED) {
            return false;
        }
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                if (f.performOptionsItemSelected(item)) {
                    return true;
                }
            }
        }
        return false;
    }
    
    public boolean dispatchContextItemSelected(MenuItem item) {
        if (mCurState < Fragment.CREATED) {
            return false;
        }
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                if (f.performContextItemSelected(item)) {
                    return true;
                }
            }
        }
        return false;
    }
    
    public void dispatchOptionsMenuClosed(Menu menu) {
        if (mCurState < Fragment.CREATED) {
            return;
        }
        for (int i = 0; i < mAdded.size(); i++) {
            Fragment f = mAdded.get(i);
            if (f != null) {
                f.performOptionsMenuClosed(menu);
            }
        }
    }

    @SuppressWarnings("ReferenceEquality")
    public void setPrimaryNavigationFragment(Fragment f) {
        if (f != null && (mActive.get(f.mIndex) != f
                || (f.mHost != null && f.getFragmentManager() != this))) {
            throw new IllegalArgumentException("Fragment " + f
                    + " is not an active fragment of FragmentManager " + this);
        }
        mPrimaryNav = f;
    }

    public Fragment getPrimaryNavigationFragment() {
        return mPrimaryNav;
    }

    public void registerFragmentLifecycleCallbacks(FragmentLifecycleCallbacks cb,
            boolean recursive) {
        mLifecycleCallbacks.add(new Pair<>(cb, recursive));
    }

    public void unregisterFragmentLifecycleCallbacks(FragmentLifecycleCallbacks cb) {
        synchronized (mLifecycleCallbacks) {
            for (int i = 0, N = mLifecycleCallbacks.size(); i < N; i++) {
                if (mLifecycleCallbacks.get(i).first == cb) {
                    mLifecycleCallbacks.remove(i);
                    break;
                }
            }
        }
    }

    void dispatchOnFragmentPreAttached(Fragment f, Context context, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentPreAttached(f, context, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentPreAttached(this, f, context);
            }
        }
    }

    void dispatchOnFragmentAttached(Fragment f, Context context, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentAttached(f, context, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentAttached(this, f, context);
            }
        }
    }

    void dispatchOnFragmentPreCreated(Fragment f, Bundle savedInstanceState,
            boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentPreCreated(f, savedInstanceState, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentPreCreated(this, f, savedInstanceState);
            }
        }
    }

    void dispatchOnFragmentCreated(Fragment f, Bundle savedInstanceState, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentCreated(f, savedInstanceState, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentCreated(this, f, savedInstanceState);
            }
        }
    }

    void dispatchOnFragmentActivityCreated(Fragment f, Bundle savedInstanceState,
            boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentActivityCreated(f, savedInstanceState, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentActivityCreated(this, f, savedInstanceState);
            }
        }
    }

    void dispatchOnFragmentViewCreated(Fragment f, View v, Bundle savedInstanceState,
            boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentViewCreated(f, v, savedInstanceState, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentViewCreated(this, f, v, savedInstanceState);
            }
        }
    }

    void dispatchOnFragmentStarted(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentStarted(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentStarted(this, f);
            }
        }
    }

    void dispatchOnFragmentResumed(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentResumed(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentResumed(this, f);
            }
        }
    }

    void dispatchOnFragmentPaused(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentPaused(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentPaused(this, f);
            }
        }
    }

    void dispatchOnFragmentStopped(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentStopped(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentStopped(this, f);
            }
        }
    }

    void dispatchOnFragmentSaveInstanceState(Fragment f, Bundle outState, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentSaveInstanceState(f, outState, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentSaveInstanceState(this, f, outState);
            }
        }
    }

    void dispatchOnFragmentViewDestroyed(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentViewDestroyed(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentViewDestroyed(this, f);
            }
        }
    }

    void dispatchOnFragmentDestroyed(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentDestroyed(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentDestroyed(this, f);
            }
        }
    }

    void dispatchOnFragmentDetached(Fragment f, boolean onlyRecursive) {
        if (mParent != null) {
            FragmentManager parentManager = mParent.getFragmentManager();
            if (parentManager instanceof FragmentManagerImpl) {
                ((FragmentManagerImpl) parentManager)
                        .dispatchOnFragmentDetached(f, true);
            }
        }
        for (Pair<FragmentLifecycleCallbacks, Boolean> p : mLifecycleCallbacks) {
            if (!onlyRecursive || p.second) {
                p.first.onFragmentDetached(this, f);
            }
        }
    }

    @Override
    public void invalidateOptionsMenu() {
        if (mHost != null && mCurState == Fragment.RESUMED) {
            mHost.onInvalidateOptionsMenu();
        } else {
            mNeedMenuInvalidate = true;
        }
    }

    public static int reverseTransit(int transit) {
        int rev = 0;
        switch (transit) {
            case FragmentTransaction.TRANSIT_FRAGMENT_OPEN:
                rev = FragmentTransaction.TRANSIT_FRAGMENT_CLOSE;
                break;
            case FragmentTransaction.TRANSIT_FRAGMENT_CLOSE:
                rev = FragmentTransaction.TRANSIT_FRAGMENT_OPEN;
                break;
            case FragmentTransaction.TRANSIT_FRAGMENT_FADE:
                rev = FragmentTransaction.TRANSIT_FRAGMENT_FADE;
                break;
        }
        return rev;
        
    }
    
    public static int transitToStyleIndex(int transit, boolean enter) {
        int animAttr = -1;
        switch (transit) {
            case FragmentTransaction.TRANSIT_FRAGMENT_OPEN:
                animAttr = enter
                    ? com.android.internal.R.styleable.FragmentAnimation_fragmentOpenEnterAnimation
                    : com.android.internal.R.styleable.FragmentAnimation_fragmentOpenExitAnimation;
                break;
            case FragmentTransaction.TRANSIT_FRAGMENT_CLOSE:
                animAttr = enter
                    ? com.android.internal.R.styleable.FragmentAnimation_fragmentCloseEnterAnimation
                    : com.android.internal.R.styleable.FragmentAnimation_fragmentCloseExitAnimation;
                break;
            case FragmentTransaction.TRANSIT_FRAGMENT_FADE:
                animAttr = enter
                    ? com.android.internal.R.styleable.FragmentAnimation_fragmentFadeEnterAnimation
                    : com.android.internal.R.styleable.FragmentAnimation_fragmentFadeExitAnimation;
                break;
        }
        return animAttr;
    }

    @Override
    public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        if (!"fragment".equals(name)) {
            return null;
        }

        String fname = attrs.getAttributeValue(null, "class");
        TypedArray a =
                context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.Fragment);
        if (fname == null) {
            fname = a.getString(com.android.internal.R.styleable.Fragment_name);
        }
        int id = a.getResourceId(com.android.internal.R.styleable.Fragment_id, View.NO_ID);
        String tag = a.getString(com.android.internal.R.styleable.Fragment_tag);
        a.recycle();

        int containerId = parent != null ? parent.getId() : 0;
        if (containerId == View.NO_ID && id == View.NO_ID && tag == null) {
            throw new IllegalArgumentException(attrs.getPositionDescription()
                    + ": Must specify unique android:id, android:tag, or have a parent with"
                    + " an id for " + fname);
        }

        // If we restored from a previous state, we may already have
        // instantiated this fragment from the state and should use
        // that instance instead of making a new one.
        Fragment fragment = id != View.NO_ID ? findFragmentById(id) : null;
        if (fragment == null && tag != null) {
            fragment = findFragmentByTag(tag);
        }
        if (fragment == null && containerId != View.NO_ID) {
            fragment = findFragmentById(containerId);
        }

        if (FragmentManagerImpl.DEBUG) Log.v(TAG, "onCreateView: id=0x"
                + Integer.toHexString(id) + " fname=" + fname
                + " existing=" + fragment);
        if (fragment == null) {
            fragment = mContainer.instantiate(context, fname, null);
            fragment.mFromLayout = true;
            fragment.mFragmentId = id != 0 ? id : containerId;
            fragment.mContainerId = containerId;
            fragment.mTag = tag;
            fragment.mInLayout = true;
            fragment.mFragmentManager = this;
            fragment.mHost = mHost;
            fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
            addFragment(fragment, true);
        } else if (fragment.mInLayout) {
            // A fragment already exists and it is not one we restored from
            // previous state.
            throw new IllegalArgumentException(attrs.getPositionDescription()
                    + ": Duplicate id 0x" + Integer.toHexString(id)
                    + ", tag " + tag + ", or parent id 0x" + Integer.toHexString(containerId)
                    + " with another fragment for " + fname);
        } else {
            // This fragment was retained from a previous instance; get it
            // going now.
            fragment.mInLayout = true;
            fragment.mHost = mHost;
            // If this fragment is newly instantiated (either right now, or
            // from last saved state), then give it the attributes to
            // initialize itself.
            if (!fragment.mRetaining) {
                fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
            }
        }

        // If we haven't finished entering the CREATED state ourselves yet,
        // push the inflated child fragment along. This will ensureInflatedFragmentView
        // at the right phase of the lifecycle so that we will have mView populated
        // for compliant fragments below.
        if (mCurState < Fragment.CREATED && fragment.mFromLayout) {
            moveToState(fragment, Fragment.CREATED, 0, 0, false);
        } else {
            moveToState(fragment);
        }

        if (fragment.mView == null) {
            throw new IllegalStateException("Fragment " + fname
                    + " did not create a view.");
        }
        if (id != 0) {
            fragment.mView.setId(id);
        }
        if (fragment.mView.getTag() == null) {
            fragment.mView.setTag(tag);
        }
        return fragment.mView;
    }

    @Override
    public View onCreateView(String name, Context context, AttributeSet attrs) {
        return null;
    }

    LayoutInflater.Factory2 getLayoutInflaterFactory() {
        return this;
    }

    
An add or pop transaction to be scheduled for the UI thread.
/**
     * An add or pop transaction to be scheduled for the UI thread.
     */
    interface OpGenerator {
        
Generate transactions to add to records and whether or not the transaction is an add or pop to isRecordPop. records and isRecordPop must be added equally so that each transaction in records matches the boolean for whether or not it is a pop in isRecordPop. 
Params:
records – A list to add transactions to.
isRecordPop – A list to add whether or not the transactions added to records is
                   a pop transaction.
Returns:
true if something was added or false otherwise./**
         * Generate transactions to add to {@code records} and whether or not the transaction is
         * an add or pop to {@code isRecordPop}.
         *
         * records and isRecordPop must be added equally so that each transaction in records
         * matches the boolean for whether or not it is a pop in isRecordPop.
         *
         * @param records A list to add transactions to.
         * @param isRecordPop A list to add whether or not the transactions added to records is
         *                    a pop transaction.
         * @return true if something was added or false otherwise.
         */
        boolean generateOps(ArrayList<BackStackRecord> records, ArrayList<Boolean> isRecordPop);
    }

    
A pop operation OpGenerator. This will be run on the UI thread and will generate the
transactions that will be popped if anything can be popped.
/**
     * A pop operation OpGenerator. This will be run on the UI thread and will generate the
     * transactions that will be popped if anything can be popped.
     */
    private class PopBackStackState implements OpGenerator {
        final String mName;
        final int mId;
        final int mFlags;

        public PopBackStackState(String name, int id, int flags) {
            mName = name;
            mId = id;
            mFlags = flags;
        }

        @Override
        public boolean generateOps(ArrayList<BackStackRecord> records,
                ArrayList<Boolean> isRecordPop) {
            if (mPrimaryNav != null // We have a primary nav fragment
                    && mId < 0 // No valid id (since they're local)
                    && mName == null) { // no name to pop to (since they're local)
                final FragmentManager childManager = mPrimaryNav.mChildFragmentManager;
                if (childManager != null && childManager.popBackStackImmediate()) {
                    // We didn't add any operations for this FragmentManager even though
                    // a child did do work.
                    return false;
                }
            }
            return popBackStackState(records, isRecordPop, mName, mId, mFlags);
        }
    }

    
A listener for a postponed transaction. This waits until Fragment.startPostponedEnterTransition() is called or a transaction is started that interacts with this one, based on interactions with the fragment container. /**
     * A listener for a postponed transaction. This waits until
     * {@link Fragment#startPostponedEnterTransition()} is called or a transaction is started
     * that interacts with this one, based on interactions with the fragment container.
     */
    static class StartEnterTransitionListener
            implements Fragment.OnStartEnterTransitionListener {
        private final boolean mIsBack;
        private final BackStackRecord mRecord;
        private int mNumPostponed;

        public StartEnterTransitionListener(BackStackRecord record, boolean isBack) {
            mIsBack = isBack;
            mRecord = record;
        }

        
Called from Fragment.startPostponedEnterTransition(), this decreases the number of Fragments that are postponed. This may cause the transaction to schedule to finish running and run transitions and animations. /**
         * Called from {@link Fragment#startPostponedEnterTransition()}, this decreases the
         * number of Fragments that are postponed. This may cause the transaction to schedule
         * to finish running and run transitions and animations.
         */
        @Override
        public void onStartEnterTransition() {
            mNumPostponed--;
            if (mNumPostponed != 0) {
                return;
            }
            mRecord.mManager.scheduleCommit();
        }

        
Called from setOnStartEnterTransitionListener.setOnStartEnterTransitionListener(OnStartEnterTransitionListener), this increases the number of fragments that are postponed as part of this transaction. /**
         * Called from {@link Fragment#
         * setOnStartEnterTransitionListener(Fragment.OnStartEnterTransitionListener)}, this
         * increases the number of fragments that are postponed as part of this transaction.
         */
        @Override
        public void startListening() {
            mNumPostponed++;
        }

        
Returns:
true if there are no more postponed fragments as part of the transaction./**
         * @return true if there are no more postponed fragments as part of the transaction.
         */
        public boolean isReady() {
            return mNumPostponed == 0;
        }

        
Completes the transaction and start the animations and transitions. This may skip the transitions if this is called before all fragments have called Fragment.startPostponedEnterTransition(). /**
         * Completes the transaction and start the animations and transitions. This may skip
         * the transitions if this is called before all fragments have called
         * {@link Fragment#startPostponedEnterTransition()}.
         */
        public void completeTransaction() {
            final boolean canceled;
            canceled = mNumPostponed > 0;
            FragmentManagerImpl manager = mRecord.mManager;
            final int numAdded = manager.mAdded.size();
            for (int i = 0; i < numAdded; i++) {
                final Fragment fragment = manager.mAdded.get(i);
                fragment.setOnStartEnterTransitionListener(null);
                if (canceled && fragment.isPostponed()) {
                    fragment.startPostponedEnterTransition();
                }
            }
            mRecord.mManager.completeExecute(mRecord, mIsBack, !canceled, true);
        }

        
Cancels this transaction instead of completing it. That means that the state isn't
changed, so the pop results in no change to the state.
/**
         * Cancels this transaction instead of completing it. That means that the state isn't
         * changed, so the pop results in no change to the state.
         */
        public void cancelTransaction() {
            mRecord.mManager.completeExecute(mRecord, mIsBack, false, false);
        }
    }
}