android/android-9.0.0_r35 : android/widget/Gallery.java

Gallery
https://source.android.com/
/*
 * Copyright (C) 2007 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.widget;

import android.annotation.NonNull;
import android.annotation.Widget;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Rect;
import android.os.Bundle;
import android.util.AttributeSet;
import android.util.Log;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.GestureDetector;
import android.view.Gravity;
import android.view.HapticFeedbackConstants;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.SoundEffectConstants;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.accessibility.AccessibilityNodeInfo;
import android.view.animation.Transformation;

import com.android.internal.R;

A view that shows items in a center-locked, horizontally scrolling list.
 The default values for the Gallery assume you will be using Theme_galleryItemBackground.Theme_galleryItemBackground as the background for each View given to the Gallery from the Adapter. If you are not doing this, you may need to adjust some Gallery properties, such as the spacing. 
 Views given to the Gallery should use LayoutParams as their layout parameters type. 
@attr ref android.R.styleable#Gallery_animationDuration
@attr ref android.R.styleable#Gallery_spacing
@attr ref android.R.styleable#Gallery_gravity
Deprecated: This widget is no longer supported. Other horizontally scrolling widgets include HorizontalScrollView and ViewPager from the support library./**
 * A view that shows items in a center-locked, horizontally scrolling list.
 * <p>
 * The default values for the Gallery assume you will be using
 * {@link android.R.styleable#Theme_galleryItemBackground} as the background for
 * each View given to the Gallery from the Adapter. If you are not doing this,
 * you may need to adjust some Gallery properties, such as the spacing.
 * <p>
 * Views given to the Gallery should use {@link Gallery.LayoutParams} as their
 * layout parameters type.
 * 
 * @attr ref android.R.styleable#Gallery_animationDuration
 * @attr ref android.R.styleable#Gallery_spacing
 * @attr ref android.R.styleable#Gallery_gravity
 * 
 * @deprecated This widget is no longer supported. Other horizontally scrolling
 * widgets include {@link HorizontalScrollView} and {@link android.support.v4.view.ViewPager}
 * from the support library.
 */
@Deprecated
@Widget
public class Gallery extends AbsSpinner implements GestureDetector.OnGestureListener {

    private static final String TAG = "Gallery";

    private static final boolean localLOGV = false;

    Duration in milliseconds from the start of a scroll during which we're
unsure whether the user is scrolling or flinging.
/**
     * Duration in milliseconds from the start of a scroll during which we're
     * unsure whether the user is scrolling or flinging.
     */
    private static final int SCROLL_TO_FLING_UNCERTAINTY_TIMEOUT = 250;

    Horizontal spacing between items.
/**
     * Horizontal spacing between items.
     */
    private int mSpacing = 0;

    How long the transition animation should run when a child view changes
position, measured in milliseconds.
/**
     * How long the transition animation should run when a child view changes
     * position, measured in milliseconds.
     */
    private int mAnimationDuration = 400;

    The alpha of items that are not selected.
/**
     * The alpha of items that are not selected.
     */
    private float mUnselectedAlpha;
    
    Left most edge of a child seen so far during layout.
/**
     * Left most edge of a child seen so far during layout.
     */
    private int mLeftMost;

    Right most edge of a child seen so far during layout.
/**
     * Right most edge of a child seen so far during layout.
     */
    private int mRightMost;

    private int mGravity;

    Helper for detecting touch gestures.
/**
     * Helper for detecting touch gestures.
     */
    private GestureDetector mGestureDetector;

    The position of the item that received the user's down touch.
/**
     * The position of the item that received the user's down touch.
     */
    private int mDownTouchPosition;

    The view of the item that received the user's down touch.
/**
     * The view of the item that received the user's down touch.
     */
    private View mDownTouchView;
    
    Executes the delta scrolls from a fling or scroll movement. 
/**
     * Executes the delta scrolls from a fling or scroll movement. 
     */
    private FlingRunnable mFlingRunnable = new FlingRunnable();

    Sets mSuppressSelectionChanged = false. This is used to set it to false
in the future. It will also trigger a selection changed.
/**
     * Sets mSuppressSelectionChanged = false. This is used to set it to false
     * in the future. It will also trigger a selection changed.
     */
    private Runnable mDisableSuppressSelectionChangedRunnable = new Runnable() {
        @Override
        public void run() {
            mSuppressSelectionChanged = false;
            selectionChanged();
        }
    };
    
    When fling runnable runs, it resets this to false. Any method along the
path until the end of its run() can set this to true to abort any
remaining fling. For example, if we've reached either the leftmost or
rightmost item, we will set this to true.
/**
     * When fling runnable runs, it resets this to false. Any method along the
     * path until the end of its run() can set this to true to abort any
     * remaining fling. For example, if we've reached either the leftmost or
     * rightmost item, we will set this to true.
     */
    private boolean mShouldStopFling;
    
    The currently selected item's child.
/**
     * The currently selected item's child.
     */
    private View mSelectedChild;
    
    Whether to continuously callback on the item selected listener during a
fling.
/**
     * Whether to continuously callback on the item selected listener during a
     * fling.
     */
    private boolean mShouldCallbackDuringFling = true;

    Whether to callback when an item that is not selected is clicked.
/**
     * Whether to callback when an item that is not selected is clicked.
     */
    private boolean mShouldCallbackOnUnselectedItemClick = true;

    If true, do not callback to item selected listener. 
/**
     * If true, do not callback to item selected listener. 
     */
    private boolean mSuppressSelectionChanged;

    If true, we have received the "invoke" (center or enter buttons) key
down. This is checked before we action on the "invoke" key up, and is
subsequently cleared.
/**
     * If true, we have received the "invoke" (center or enter buttons) key
     * down. This is checked before we action on the "invoke" key up, and is
     * subsequently cleared.
     */
    private boolean mReceivedInvokeKeyDown;
    
    private AdapterContextMenuInfo mContextMenuInfo;

    If true, this onScroll is the first for this user's drag (remember, a
drag sends many onScrolls).
/**
     * If true, this onScroll is the first for this user's drag (remember, a
     * drag sends many onScrolls).
     */
    private boolean mIsFirstScroll;

    If true, mFirstPosition is the position of the rightmost child, and
the children are ordered right to left.
/**
     * If true, mFirstPosition is the position of the rightmost child, and
     * the children are ordered right to left.
     */
    private boolean mIsRtl = true;
    
    Offset between the center of the selected child view and the center of the Gallery.
Used to reset position correctly during layout.
/**
     * Offset between the center of the selected child view and the center of the Gallery.
     * Used to reset position correctly during layout.
     */
    private int mSelectedCenterOffset;

    public Gallery(Context context) {
        this(context, null);
    }

    public Gallery(Context context, AttributeSet attrs) {
        this(context, attrs, R.attr.galleryStyle);
    }

    public Gallery(Context context, AttributeSet attrs, int defStyleAttr) {
        this(context, attrs, defStyleAttr, 0);
    }

    public Gallery(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);

        final TypedArray a = context.obtainStyledAttributes(
                attrs, com.android.internal.R.styleable.Gallery, defStyleAttr, defStyleRes);

        int index = a.getInt(com.android.internal.R.styleable.Gallery_gravity, -1);
        if (index >= 0) {
            setGravity(index);
        }

        int animationDuration =
                a.getInt(com.android.internal.R.styleable.Gallery_animationDuration, -1);
        if (animationDuration > 0) {
            setAnimationDuration(animationDuration);
        }

        int spacing =
                a.getDimensionPixelOffset(com.android.internal.R.styleable.Gallery_spacing, 0);
        setSpacing(spacing);

        float unselectedAlpha = a.getFloat(
                com.android.internal.R.styleable.Gallery_unselectedAlpha, 0.5f);
        setUnselectedAlpha(unselectedAlpha);
        
        a.recycle();

        // We draw the selected item last (because otherwise the item to the
        // right overlaps it)
        mGroupFlags |= FLAG_USE_CHILD_DRAWING_ORDER;
        
        mGroupFlags |= FLAG_SUPPORT_STATIC_TRANSFORMATIONS;
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();

        if (mGestureDetector == null) {
            mGestureDetector = new GestureDetector(getContext(), this);
            mGestureDetector.setIsLongpressEnabled(true);
        }
    }

    Whether or not to callback on any AdapterView<SpinnerAdapter>.getOnItemSelectedListener() while the items are being flinged. If false, only the final selected item will cause the callback. If true, all items between the first and the final will cause callbacks. 
Params: shouldCallback – Whether or not to callback on the listener while
           the items are being flinged./**
     * Whether or not to callback on any {@link #getOnItemSelectedListener()}
     * while the items are being flinged. If false, only the final selected item
     * will cause the callback. If true, all items between the first and the
     * final will cause callbacks.
     * 
     * @param shouldCallback Whether or not to callback on the listener while
     *            the items are being flinged.
     */
    public void setCallbackDuringFling(boolean shouldCallback) {
        mShouldCallbackDuringFling = shouldCallback;
    }

    Whether or not to callback when an item that is not selected is clicked. If false, the item will become selected (and re-centered). If true, the AdapterView<SpinnerAdapter>.getOnItemClickListener() will get the callback. 
Params: shouldCallback – Whether or not to callback on the listener when a
           item that is not selected is clicked.
@hide /**
     * Whether or not to callback when an item that is not selected is clicked.
     * If false, the item will become selected (and re-centered). If true, the
     * {@link #getOnItemClickListener()} will get the callback.
     * 
     * @param shouldCallback Whether or not to callback on the listener when a
     *            item that is not selected is clicked.
     * @hide
     */
    public void setCallbackOnUnselectedItemClick(boolean shouldCallback) {
        mShouldCallbackOnUnselectedItemClick = shouldCallback;
    }
    
    Sets how long the transition animation should run when a child view
changes position. Only relevant if animation is turned on.
Params: animationDurationMillis – The duration of the transition, in
       milliseconds.
@attr ref android.R.styleable#Gallery_animationDuration/**
     * Sets how long the transition animation should run when a child view
     * changes position. Only relevant if animation is turned on.
     * 
     * @param animationDurationMillis The duration of the transition, in
     *        milliseconds.
     * 
     * @attr ref android.R.styleable#Gallery_animationDuration
     */
    public void setAnimationDuration(int animationDurationMillis) {
        mAnimationDuration = animationDurationMillis;
    }

    Sets the spacing between items in a Gallery
Params: spacing – The spacing in pixels between items in the Gallery
@attr ref android.R.styleable#Gallery_spacing/**
     * Sets the spacing between items in a Gallery
     * 
     * @param spacing The spacing in pixels between items in the Gallery
     * 
     * @attr ref android.R.styleable#Gallery_spacing
     */
    public void setSpacing(int spacing) {
        mSpacing = spacing;
    }

    Sets the alpha of items that are not selected in the Gallery.
Params: unselectedAlpha – the alpha for the items that are not selected.
@attr ref android.R.styleable#Gallery_unselectedAlpha/**
     * Sets the alpha of items that are not selected in the Gallery.
     * 
     * @param unselectedAlpha the alpha for the items that are not selected.
     * 
     * @attr ref android.R.styleable#Gallery_unselectedAlpha
     */
    public void setUnselectedAlpha(float unselectedAlpha) {
        mUnselectedAlpha = unselectedAlpha;
    }

    @Override
    protected boolean getChildStaticTransformation(View child, Transformation t) {
        
        t.clear();
        t.setAlpha(child == mSelectedChild ? 1.0f : mUnselectedAlpha);
        
        return true;
    }

    @Override
    protected int computeHorizontalScrollExtent() {
        // Only 1 item is considered to be selected
        return 1;
    }

    @Override
    protected int computeHorizontalScrollOffset() {
        // Current scroll position is the same as the selected position
        return mSelectedPosition;
    }

    @Override
    protected int computeHorizontalScrollRange() {
        // Scroll range is the same as the item count
        return mItemCount;
    }

    @Override
    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
        return p instanceof LayoutParams;
    }

    @Override
    protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
        return new LayoutParams(p);
    }

    @Override
    public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }

    @Override
    protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
        /*
         * Gallery expects Gallery.LayoutParams.
         */
        return new Gallery.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        
        /*
         * Remember that we are in layout to prevent more layout request from
         * being generated.
         */
        mInLayout = true;
        layout(0, false);
        mInLayout = false;
    }

    @Override
    int getChildHeight(View child) {
        return child.getMeasuredHeight();
    }

    Tracks a motion scroll. In reality, this is used to do just about any
movement to items (touch scroll, arrow-key scroll, set an item as selected).
Params: deltaX – Change in X from the previous event./**
     * Tracks a motion scroll. In reality, this is used to do just about any
     * movement to items (touch scroll, arrow-key scroll, set an item as selected).
     * 
     * @param deltaX Change in X from the previous event.
     */
    void trackMotionScroll(int deltaX) {

        if (getChildCount() == 0) {
            return;
        }
        
        boolean toLeft = deltaX < 0; 
        
        int limitedDeltaX = getLimitedMotionScrollAmount(toLeft, deltaX);
        if (limitedDeltaX != deltaX) {
            // The above call returned a limited amount, so stop any scrolls/flings
            mFlingRunnable.endFling(false);
            onFinishedMovement();
        }
        
        offsetChildrenLeftAndRight(limitedDeltaX);
        
        detachOffScreenChildren(toLeft);
        
        if (toLeft) {
            // If moved left, there will be empty space on the right
            fillToGalleryRight();
        } else {
            // Similarly, empty space on the left
            fillToGalleryLeft();
        }
        
        // Clear unused views
        mRecycler.clear();
        
        setSelectionToCenterChild();

        final View selChild = mSelectedChild;
        if (selChild != null) {
            final int childLeft = selChild.getLeft();
            final int childCenter = selChild.getWidth() / 2;
            final int galleryCenter = getWidth() / 2;
            mSelectedCenterOffset = childLeft + childCenter - galleryCenter;
        }

        onScrollChanged(0, 0, 0, 0); // dummy values, View's implementation does not use these.

        invalidate();
    }

    int getLimitedMotionScrollAmount(boolean motionToLeft, int deltaX) {
        int extremeItemPosition = motionToLeft != mIsRtl ? mItemCount - 1 : 0;
        View extremeChild = getChildAt(extremeItemPosition - mFirstPosition);
        
        if (extremeChild == null) {
            return deltaX;
        }
        
        int extremeChildCenter = getCenterOfView(extremeChild);
        int galleryCenter = getCenterOfGallery();
        
        if (motionToLeft) {
            if (extremeChildCenter <= galleryCenter) {
                
                // The extreme child is past his boundary point!
                return 0;
            }
        } else {
            if (extremeChildCenter >= galleryCenter) {

                // The extreme child is past his boundary point!
                return 0;
            }
        }
        
        int centerDifference = galleryCenter - extremeChildCenter;

        return motionToLeft
                ? Math.max(centerDifference, deltaX)
                : Math.min(centerDifference, deltaX); 
    }

    Offset the horizontal location of all children of this view by the
specified number of pixels.
Params: offset – the number of pixels to offset/**
     * Offset the horizontal location of all children of this view by the
     * specified number of pixels.
     * 
     * @param offset the number of pixels to offset
     */
    private void offsetChildrenLeftAndRight(int offset) {
        for (int i = getChildCount() - 1; i >= 0; i--) {
            getChildAt(i).offsetLeftAndRight(offset);
        }
    }
    
    Returns: The center of this Gallery./**
     * @return The center of this Gallery.
     */
    private int getCenterOfGallery() {
        return (getWidth() - mPaddingLeft - mPaddingRight) / 2 + mPaddingLeft;
    }
    
    Returns: The center of the given view./**
     * @return The center of the given view.
     */
    private static int getCenterOfView(View view) {
        return view.getLeft() + view.getWidth() / 2;
    }
    
    Detaches children that are off the screen (i.e.: Gallery bounds).
Params: toLeft – Whether to detach children to the left of the Gallery, or
           to the right./**
     * Detaches children that are off the screen (i.e.: Gallery bounds).
     * 
     * @param toLeft Whether to detach children to the left of the Gallery, or
     *            to the right.
     */
    private void detachOffScreenChildren(boolean toLeft) {
        int numChildren = getChildCount();
        int firstPosition = mFirstPosition;
        int start = 0;
        int count = 0;

        if (toLeft) {
            final int galleryLeft = mPaddingLeft;
            for (int i = 0; i < numChildren; i++) {
                int n = mIsRtl ? (numChildren - 1 - i) : i;
                final View child = getChildAt(n);
                if (child.getRight() >= galleryLeft) {
                    break;
                } else {
                    start = n;
                    count++;
                    mRecycler.put(firstPosition + n, child);
                }
            }
            if (!mIsRtl) {
                start = 0;
            }
        } else {
            final int galleryRight = getWidth() - mPaddingRight;
            for (int i = numChildren - 1; i >= 0; i--) {
                int n = mIsRtl ? numChildren - 1 - i : i;
                final View child = getChildAt(n);
                if (child.getLeft() <= galleryRight) {
                    break;
                } else {
                    start = n;
                    count++;
                    mRecycler.put(firstPosition + n, child);
                }
            }
            if (mIsRtl) {
                start = 0;
            }
        }

        detachViewsFromParent(start, count);
        
        if (toLeft != mIsRtl) {
            mFirstPosition += count;
        }
    }
    
    Scrolls the items so that the selected item is in its 'slot' (its center
is the gallery's center).
/**
     * Scrolls the items so that the selected item is in its 'slot' (its center
     * is the gallery's center).
     */
    private void scrollIntoSlots() {
        
        if (getChildCount() == 0 || mSelectedChild == null) return;
        
        int selectedCenter = getCenterOfView(mSelectedChild);
        int targetCenter = getCenterOfGallery();
        
        int scrollAmount = targetCenter - selectedCenter;
        if (scrollAmount != 0) {
            mFlingRunnable.startUsingDistance(scrollAmount);
        } else {
            onFinishedMovement();
        }
    }

    private void onFinishedMovement() {
        if (mSuppressSelectionChanged) {
            mSuppressSelectionChanged = false;
            
            // We haven't been callbacking during the fling, so do it now
            super.selectionChanged();
        }
        mSelectedCenterOffset = 0;
        invalidate();
    }
    
    @Override
    void selectionChanged() {
        if (!mSuppressSelectionChanged) {
            super.selectionChanged();
        }
    }

    Looks for the child that is closest to the center and sets it as the
selected child.
/**
     * Looks for the child that is closest to the center and sets it as the
     * selected child.
     */
    private void setSelectionToCenterChild() {
        
        View selView = mSelectedChild;
        if (mSelectedChild == null) return;
        
        int galleryCenter = getCenterOfGallery();
        
        // Common case where the current selected position is correct
        if (selView.getLeft() <= galleryCenter && selView.getRight() >= galleryCenter) {
            return;
        }
        
        // TODO better search
        int closestEdgeDistance = Integer.MAX_VALUE;
        int newSelectedChildIndex = 0;
        for (int i = getChildCount() - 1; i >= 0; i--) {
            
            View child = getChildAt(i);
            
            if (child.getLeft() <= galleryCenter && child.getRight() >=  galleryCenter) {
                // This child is in the center
                newSelectedChildIndex = i;
                break;
            }
            
            int childClosestEdgeDistance = Math.min(Math.abs(child.getLeft() - galleryCenter),
                    Math.abs(child.getRight() - galleryCenter));
            if (childClosestEdgeDistance < closestEdgeDistance) {
                closestEdgeDistance = childClosestEdgeDistance;
                newSelectedChildIndex = i;
            }
        }
        
        int newPos = mFirstPosition + newSelectedChildIndex;
        
        if (newPos != mSelectedPosition) {
            setSelectedPositionInt(newPos);
            setNextSelectedPositionInt(newPos);
            checkSelectionChanged();
        }
    }

    Creates and positions all views for this Gallery.
 We layout rarely, most of the time trackMotionScroll(int) takes care of repositioning, adding, and removing children. 
Params: delta – Change in the selected position. +1 means the selection is
           moving to the right, so views are scrolling to the left. -1
           means the selection is moving to the left./**
     * Creates and positions all views for this Gallery.
     * <p>
     * We layout rarely, most of the time {@link #trackMotionScroll(int)} takes
     * care of repositioning, adding, and removing children.
     * 
     * @param delta Change in the selected position. +1 means the selection is
     *            moving to the right, so views are scrolling to the left. -1
     *            means the selection is moving to the left.
     */
    @Override
    void layout(int delta, boolean animate) {

        mIsRtl = isLayoutRtl();

        int childrenLeft = mSpinnerPadding.left;
        int childrenWidth = mRight - mLeft - mSpinnerPadding.left - mSpinnerPadding.right;

        if (mDataChanged) {
            handleDataChanged();
        }

        // Handle an empty gallery by removing all views.
        if (mItemCount == 0) {
            resetList();
            return;
        }

        // Update to the new selected position.
        if (mNextSelectedPosition >= 0) {
            setSelectedPositionInt(mNextSelectedPosition);
        }

        // All views go in recycler while we are in layout
        recycleAllViews();

        // Clear out old views
        //removeAllViewsInLayout();
        detachAllViewsFromParent();

        /*
         * These will be used to give initial positions to views entering the
         * gallery as we scroll
         */
        mRightMost = 0;
        mLeftMost = 0;

        // Make selected view and center it
        
        /*
         * mFirstPosition will be decreased as we add views to the left later
         * on. The 0 for x will be offset in a couple lines down.
         */  
        mFirstPosition = mSelectedPosition;
        View sel = makeAndAddView(mSelectedPosition, 0, 0, true);
        
        // Put the selected child in the center
        int selectedOffset = childrenLeft + (childrenWidth / 2) - (sel.getWidth() / 2) +
                mSelectedCenterOffset;
        sel.offsetLeftAndRight(selectedOffset);

        fillToGalleryRight();
        fillToGalleryLeft();
        
        // Flush any cached views that did not get reused above
        mRecycler.clear();

        invalidate();
        checkSelectionChanged();

        mDataChanged = false;
        mNeedSync = false;
        setNextSelectedPositionInt(mSelectedPosition);
        
        updateSelectedItemMetadata();
    }

    private void fillToGalleryLeft() {
        if (mIsRtl) {
            fillToGalleryLeftRtl();
        } else {
            fillToGalleryLeftLtr();
        }
    }

    private void fillToGalleryLeftRtl() {
        int itemSpacing = mSpacing;
        int galleryLeft = mPaddingLeft;
        int numChildren = getChildCount();
        int numItems = mItemCount;

        // Set state for initial iteration
        View prevIterationView = getChildAt(numChildren - 1);
        int curPosition;
        int curRightEdge;

        if (prevIterationView != null) {
            curPosition = mFirstPosition + numChildren;
            curRightEdge = prevIterationView.getLeft() - itemSpacing;
        } else {
            // No children available!
            mFirstPosition = curPosition = mItemCount - 1;
            curRightEdge = mRight - mLeft - mPaddingRight;
            mShouldStopFling = true;
        }

        while (curRightEdge > galleryLeft && curPosition < mItemCount) {
            prevIterationView = makeAndAddView(curPosition, curPosition - mSelectedPosition,
                    curRightEdge, false);

            // Set state for next iteration
            curRightEdge = prevIterationView.getLeft() - itemSpacing;
            curPosition++;
        }
    }

    private void fillToGalleryLeftLtr() {
        int itemSpacing = mSpacing;
        int galleryLeft = mPaddingLeft;
        
        // Set state for initial iteration
        View prevIterationView = getChildAt(0);
        int curPosition;
        int curRightEdge;
        
        if (prevIterationView != null) {
            curPosition = mFirstPosition - 1;
            curRightEdge = prevIterationView.getLeft() - itemSpacing;
        } else {
            // No children available!
            curPosition = 0; 
            curRightEdge = mRight - mLeft - mPaddingRight;
            mShouldStopFling = true;
        }
                
        while (curRightEdge > galleryLeft && curPosition >= 0) {
            prevIterationView = makeAndAddView(curPosition, curPosition - mSelectedPosition,
                    curRightEdge, false);

            // Remember some state
            mFirstPosition = curPosition;
            
            // Set state for next iteration
            curRightEdge = prevIterationView.getLeft() - itemSpacing;
            curPosition--;
        }
    }
    
    private void fillToGalleryRight() {
        if (mIsRtl) {
            fillToGalleryRightRtl();
        } else {
            fillToGalleryRightLtr();
        }
    }

    private void fillToGalleryRightRtl() {
        int itemSpacing = mSpacing;
        int galleryRight = mRight - mLeft - mPaddingRight;

        // Set state for initial iteration
        View prevIterationView = getChildAt(0);
        int curPosition;
        int curLeftEdge;

        if (prevIterationView != null) {
            curPosition = mFirstPosition -1;
            curLeftEdge = prevIterationView.getRight() + itemSpacing;
        } else {
            curPosition = 0;
            curLeftEdge = mPaddingLeft;
            mShouldStopFling = true;
        }

        while (curLeftEdge < galleryRight && curPosition >= 0) {
            prevIterationView = makeAndAddView(curPosition, curPosition - mSelectedPosition,
                    curLeftEdge, true);

            // Remember some state
            mFirstPosition = curPosition;

            // Set state for next iteration
            curLeftEdge = prevIterationView.getRight() + itemSpacing;
            curPosition--;
        }
    }

    private void fillToGalleryRightLtr() {
        int itemSpacing = mSpacing;
        int galleryRight = mRight - mLeft - mPaddingRight;
        int numChildren = getChildCount();
        int numItems = mItemCount;
        
        // Set state for initial iteration
        View prevIterationView = getChildAt(numChildren - 1);
        int curPosition;
        int curLeftEdge;
        
        if (prevIterationView != null) {
            curPosition = mFirstPosition + numChildren;
            curLeftEdge = prevIterationView.getRight() + itemSpacing;
        } else {
            mFirstPosition = curPosition = mItemCount - 1;
            curLeftEdge = mPaddingLeft;
            mShouldStopFling = true;
        }
                
        while (curLeftEdge < galleryRight && curPosition < numItems) {
            prevIterationView = makeAndAddView(curPosition, curPosition - mSelectedPosition,
                    curLeftEdge, true);

            // Set state for next iteration
            curLeftEdge = prevIterationView.getRight() + itemSpacing;
            curPosition++;
        }
    }

    Obtain a view, either by pulling an existing view from the recycler or by
getting a new one from the adapter. If we are animating, make sure there
is enough information in the view's layout parameters to animate from the
old to new positions.
Params: position – Position in the gallery for the view to obtain
offset – Offset from the selected position
x – X-coordinate indicating where this view should be placed. This
       will either be the left or right edge of the view, depending on
       the fromLeft parameter
fromLeft – Are we positioning views based on the left edge? (i.e.,
       building from left to right)?
Returns: A view that has been added to the gallery/**
     * Obtain a view, either by pulling an existing view from the recycler or by
     * getting a new one from the adapter. If we are animating, make sure there
     * is enough information in the view's layout parameters to animate from the
     * old to new positions.
     * 
     * @param position Position in the gallery for the view to obtain
     * @param offset Offset from the selected position
     * @param x X-coordinate indicating where this view should be placed. This
     *        will either be the left or right edge of the view, depending on
     *        the fromLeft parameter
     * @param fromLeft Are we positioning views based on the left edge? (i.e.,
     *        building from left to right)?
     * @return A view that has been added to the gallery
     */
    private View makeAndAddView(int position, int offset, int x, boolean fromLeft) {

        View child;
        if (!mDataChanged) {
            child = mRecycler.get(position);
            if (child != null) {
                // Can reuse an existing view
                int childLeft = child.getLeft();
                
                // Remember left and right edges of where views have been placed
                mRightMost = Math.max(mRightMost, childLeft 
                        + child.getMeasuredWidth());
                mLeftMost = Math.min(mLeftMost, childLeft);

                // Position the view
                setUpChild(child, offset, x, fromLeft);

                return child;
            }
        }

        // Nothing found in the recycler -- ask the adapter for a view
        child = mAdapter.getView(position, null, this);

        // Position the view
        setUpChild(child, offset, x, fromLeft);

        return child;
    }

    Helper for makeAndAddView to set the position of a view and fill out its
layout parameters.
Params: child – The view to position
offset – Offset from the selected position
x – X-coordinate indicating where this view should be placed. This
       will either be the left or right edge of the view, depending on
       the fromLeft parameter
fromLeft – Are we positioning views based on the left edge? (i.e.,
       building from left to right)?/**
     * Helper for makeAndAddView to set the position of a view and fill out its
     * layout parameters.
     * 
     * @param child The view to position
     * @param offset Offset from the selected position
     * @param x X-coordinate indicating where this view should be placed. This
     *        will either be the left or right edge of the view, depending on
     *        the fromLeft parameter
     * @param fromLeft Are we positioning views based on the left edge? (i.e.,
     *        building from left to right)?
     */
    private void setUpChild(View child, int offset, int x, boolean fromLeft) {

        // Respect layout params that are already in the view. Otherwise
        // make some up...
        Gallery.LayoutParams lp = (Gallery.LayoutParams) child.getLayoutParams();
        if (lp == null) {
            lp = (Gallery.LayoutParams) generateDefaultLayoutParams();
        }

        addViewInLayout(child, fromLeft != mIsRtl ? -1 : 0, lp, true);

        child.setSelected(offset == 0);

        // Get measure specs
        int childHeightSpec = ViewGroup.getChildMeasureSpec(mHeightMeasureSpec,
                mSpinnerPadding.top + mSpinnerPadding.bottom, lp.height);
        int childWidthSpec = ViewGroup.getChildMeasureSpec(mWidthMeasureSpec,
                mSpinnerPadding.left + mSpinnerPadding.right, lp.width);

        // Measure child
        child.measure(childWidthSpec, childHeightSpec);

        int childLeft;
        int childRight;

        // Position vertically based on gravity setting
        int childTop = calculateTop(child, true);
        int childBottom = childTop + child.getMeasuredHeight();

        int width = child.getMeasuredWidth();
        if (fromLeft) {
            childLeft = x;
            childRight = childLeft + width;
        } else {
            childLeft = x - width;
            childRight = x;
        }

        child.layout(childLeft, childTop, childRight, childBottom);
    }

    Figure out vertical placement based on mGravity
Params: child – Child to place
Returns: Where the top of the child should be/**
     * Figure out vertical placement based on mGravity
     * 
     * @param child Child to place
     * @return Where the top of the child should be
     */
    private int calculateTop(View child, boolean duringLayout) {
        int myHeight = duringLayout ? getMeasuredHeight() : getHeight();
        int childHeight = duringLayout ? child.getMeasuredHeight() : child.getHeight(); 
        
        int childTop = 0;

        switch (mGravity) {
        case Gravity.TOP:
            childTop = mSpinnerPadding.top;
            break;
        case Gravity.CENTER_VERTICAL:
            int availableSpace = myHeight - mSpinnerPadding.bottom
                    - mSpinnerPadding.top - childHeight;
            childTop = mSpinnerPadding.top + (availableSpace / 2);
            break;
        case Gravity.BOTTOM:
            childTop = myHeight - mSpinnerPadding.bottom - childHeight;
            break;
        }
        return childTop;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        // Give everything to the gesture detector
        boolean retValue = mGestureDetector.onTouchEvent(event);

        int action = event.getAction();
        if (action == MotionEvent.ACTION_UP) {
            // Helper method for lifted finger
            onUp();
        } else if (action == MotionEvent.ACTION_CANCEL) {
            onCancel();
        }
        
        return retValue;
    }
    
    @Override
    public boolean onSingleTapUp(MotionEvent e) {

        if (mDownTouchPosition >= 0) {
            
            // An item tap should make it selected, so scroll to this child.
            scrollToChild(mDownTouchPosition - mFirstPosition);

            // Also pass the click so the client knows, if it wants to.
            if (mShouldCallbackOnUnselectedItemClick || mDownTouchPosition == mSelectedPosition) {
                performItemClick(mDownTouchView, mDownTouchPosition, mAdapter
                        .getItemId(mDownTouchPosition));
            }
            
            return true;
        }
        
        return false;
    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        
        if (!mShouldCallbackDuringFling) {
            // We want to suppress selection changes
            
            // Remove any future code to set mSuppressSelectionChanged = false
            removeCallbacks(mDisableSuppressSelectionChangedRunnable);

            // This will get reset once we scroll into slots
            if (!mSuppressSelectionChanged) mSuppressSelectionChanged = true;
        }
        
        // Fling the gallery!
        mFlingRunnable.startUsingVelocity((int) -velocityX);
        
        return true;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {

        if (localLOGV) Log.v(TAG, String.valueOf(e2.getX() - e1.getX()));
        
        /*
         * Now's a good time to tell our parent to stop intercepting our events!
         * The user has moved more than the slop amount, since GestureDetector
         * ensures this before calling this method. Also, if a parent is more
         * interested in this touch's events than we are, it would have
         * intercepted them by now (for example, we can assume when a Gallery is
         * in the ListView, a vertical scroll would not end up in this method
         * since a ListView would have intercepted it by now).
         */
        mParent.requestDisallowInterceptTouchEvent(true);
        
        // As the user scrolls, we want to callback selection changes so related-
        // info on the screen is up-to-date with the gallery's selection
        if (!mShouldCallbackDuringFling) {
            if (mIsFirstScroll) {
                /*
                 * We're not notifying the client of selection changes during
                 * the fling, and this scroll could possibly be a fling. Don't
                 * do selection changes until we're sure it is not a fling.
                 */
                if (!mSuppressSelectionChanged) mSuppressSelectionChanged = true;
                postDelayed(mDisableSuppressSelectionChangedRunnable, SCROLL_TO_FLING_UNCERTAINTY_TIMEOUT);
            }
        } else {
            if (mSuppressSelectionChanged) mSuppressSelectionChanged = false;
        }
        
        // Track the motion
        trackMotionScroll(-1 * (int) distanceX);
       
        mIsFirstScroll = false;
        return true;
    }
    
    @Override
    public boolean onDown(MotionEvent e) {

        // Kill any existing fling/scroll
        mFlingRunnable.stop(false);

        // Get the item's view that was touched
        mDownTouchPosition = pointToPosition((int) e.getX(), (int) e.getY());
        
        if (mDownTouchPosition >= 0) {
            mDownTouchView = getChildAt(mDownTouchPosition - mFirstPosition);
            mDownTouchView.setPressed(true);
        }
        
        // Reset the multiple-scroll tracking state
        mIsFirstScroll = true;
        
        // Must return true to get matching events for this down event.
        return true;
    }

    Called when a touch event's action is MotionEvent.ACTION_UP.
/**
     * Called when a touch event's action is MotionEvent.ACTION_UP.
     */
    void onUp() {
        
        if (mFlingRunnable.mScroller.isFinished()) {
            scrollIntoSlots();
        }
        
        dispatchUnpress();
    }
    
    Called when a touch event's action is MotionEvent.ACTION_CANCEL.
/**
     * Called when a touch event's action is MotionEvent.ACTION_CANCEL.
     */
    void onCancel() {
        onUp();
    }
    
    @Override
    public void onLongPress(@NonNull MotionEvent e) {
        if (mDownTouchPosition < 0) {
            return;
        }
        
        performHapticFeedback(HapticFeedbackConstants.LONG_PRESS);

        final long id = getItemIdAtPosition(mDownTouchPosition);
        dispatchLongPress(mDownTouchView, mDownTouchPosition, id, e.getX(), e.getY(), true);
    }

    // Unused methods from GestureDetector.OnGestureListener below
    
    @Override
    public void onShowPress(MotionEvent e) {
    }

    // Unused methods from GestureDetector.OnGestureListener above
    
    private void dispatchPress(View child) {
        
        if (child != null) {
            child.setPressed(true);
        }
        
        setPressed(true);
    }
    
    private void dispatchUnpress() {
        
        for (int i = getChildCount() - 1; i >= 0; i--) {
            getChildAt(i).setPressed(false);
        }
        
        setPressed(false);
    }
    
    @Override
    public void dispatchSetSelected(boolean selected) {
        /*
         * We don't want to pass the selected state given from its parent to its
         * children since this widget itself has a selected state to give to its
         * children.
         */
    }

    @Override
    protected void dispatchSetPressed(boolean pressed) {
        
        // Show the pressed state on the selected child
        if (mSelectedChild != null) {
            mSelectedChild.setPressed(pressed);
        }
    }

    @Override
    protected ContextMenuInfo getContextMenuInfo() {
        return mContextMenuInfo;
    }

    @Override
    public boolean showContextMenuForChild(View originalView) {
        if (isShowingContextMenuWithCoords()) {
            return false;
        }
        return showContextMenuForChildInternal(originalView, 0, 0, false);
    }

    @Override
    public boolean showContextMenuForChild(View originalView, float x, float y) {
        return showContextMenuForChildInternal(originalView, x, y, true);
    }

    private boolean showContextMenuForChildInternal(View originalView, float x, float y,
            boolean useOffsets) {
        final int longPressPosition = getPositionForView(originalView);
        if (longPressPosition < 0) {
            return false;
        }
        
        final long longPressId = mAdapter.getItemId(longPressPosition);
        return dispatchLongPress(originalView, longPressPosition, longPressId, x, y, useOffsets);
    }

    @Override
    public boolean showContextMenu() {
        return showContextMenuInternal(0, 0, false);
    }

    @Override
    public boolean showContextMenu(float x, float y) {
        return showContextMenuInternal(x, y, true);
    }

    private boolean showContextMenuInternal(float x, float y, boolean useOffsets) {
        if (isPressed() && mSelectedPosition >= 0) {
            final int index = mSelectedPosition - mFirstPosition;
            final View v = getChildAt(index);
            return dispatchLongPress(v, mSelectedPosition, mSelectedRowId, x, y, useOffsets);
        }        
        
        return false;
    }

    private boolean dispatchLongPress(View view, int position, long id, float x, float y,
            boolean useOffsets) {
        boolean handled = false;
        
        if (mOnItemLongClickListener != null) {
            handled = mOnItemLongClickListener.onItemLongClick(this, mDownTouchView,
                    mDownTouchPosition, id);
        }

        if (!handled) {
            mContextMenuInfo = new AdapterContextMenuInfo(view, position, id);

            if (useOffsets) {
                handled = super.showContextMenuForChild(view, x, y);
            } else {
                handled = super.showContextMenuForChild(this);
            }
        }

        if (handled) {
            performHapticFeedback(HapticFeedbackConstants.LONG_PRESS);
        }
        
        return handled;
    }
    
    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        // Gallery steals all key events
        return event.dispatch(this, null, null);
    }

    Handles left, right, and clicking
See Also: onKeyDown.onKeyDown/**
     * Handles left, right, and clicking
     * @see android.view.View#onKeyDown
     */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch (keyCode) {
            
        case KeyEvent.KEYCODE_DPAD_LEFT:
            if (moveDirection(-1)) {
                playSoundEffect(SoundEffectConstants.NAVIGATION_LEFT);
                return true;
            }
            break;
        case KeyEvent.KEYCODE_DPAD_RIGHT:
            if (moveDirection(1)) {
                playSoundEffect(SoundEffectConstants.NAVIGATION_RIGHT);
                return true;
            }
            break;
        case KeyEvent.KEYCODE_DPAD_CENTER:
        case KeyEvent.KEYCODE_ENTER:
            mReceivedInvokeKeyDown = true;
            // fallthrough to default handling
        }
        
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (KeyEvent.isConfirmKey(keyCode)) {
            if (mReceivedInvokeKeyDown) {
                if (mItemCount > 0) {
                    dispatchPress(mSelectedChild);
                    postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            dispatchUnpress();
                        }
                    }, ViewConfiguration.getPressedStateDuration());

                    int selectedIndex = mSelectedPosition - mFirstPosition;
                    performItemClick(getChildAt(selectedIndex), mSelectedPosition, mAdapter
                            .getItemId(mSelectedPosition));
                }
            }

            // Clear the flag
            mReceivedInvokeKeyDown = false;
            return true;
        }
        return super.onKeyUp(keyCode, event);
    }
    
    boolean moveDirection(int direction) {
        direction = isLayoutRtl() ? -direction : direction;
        int targetPosition = mSelectedPosition + direction;

        if (mItemCount > 0 && targetPosition >= 0 && targetPosition < mItemCount) {
            scrollToChild(targetPosition - mFirstPosition);
            return true;
        } else {
            return false;
        }
    }

    private boolean scrollToChild(int childPosition) {
        View child = getChildAt(childPosition);
        
        if (child != null) {
            int distance = getCenterOfGallery() - getCenterOfView(child);
            mFlingRunnable.startUsingDistance(distance);
            return true;
        }
        
        return false;
    }
    
    @Override
    void setSelectedPositionInt(int position) {
        super.setSelectedPositionInt(position);

        // Updates any metadata we keep about the selected item.
        updateSelectedItemMetadata();
    }

    private void updateSelectedItemMetadata() {
        
        View oldSelectedChild = mSelectedChild;

        View child = mSelectedChild = getChildAt(mSelectedPosition - mFirstPosition);
        if (child == null) {
            return;
        }

        child.setSelected(true);
        child.setFocusable(true);

        if (hasFocus()) {
            child.requestFocus();
        }

        // We unfocus the old child down here so the above hasFocus check
        // returns true
        if (oldSelectedChild != null && oldSelectedChild != child) {

            // Make sure its drawable state doesn't contain 'selected'
            oldSelectedChild.setSelected(false);
            
            // Make sure it is not focusable anymore, since otherwise arrow keys
            // can make this one be focused
            oldSelectedChild.setFocusable(false);
        }
        
    }
    
    Describes how the child views are aligned.
Params: gravity – 
@attr ref android.R.styleable#Gallery_gravity/**
     * Describes how the child views are aligned.
     * @param gravity
     * 
     * @attr ref android.R.styleable#Gallery_gravity
     */
    public void setGravity(int gravity)
    {
        if (mGravity != gravity) {
            mGravity = gravity;
            requestLayout();
        }
    }

    @Override
    protected int getChildDrawingOrder(int childCount, int i) {
        int selectedIndex = mSelectedPosition - mFirstPosition;
        
        // Just to be safe
        if (selectedIndex < 0) return i;
        
        if (i == childCount - 1) {
            // Draw the selected child last
            return selectedIndex;
        } else if (i >= selectedIndex) {
            // Move the children after the selected child earlier one
            return i + 1;
        } else {
            // Keep the children before the selected child the same
            return i;
        }
    }

    @Override
    protected void onFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect) {
        super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
        
        /*
         * The gallery shows focus by focusing the selected item. So, give
         * focus to our selected item instead. We steal keys from our
         * selected item elsewhere.
         */
        if (gainFocus && mSelectedChild != null) {
            mSelectedChild.requestFocus(direction);
            mSelectedChild.setSelected(true);
        }

    }

    @Override
    public CharSequence getAccessibilityClassName() {
        return Gallery.class.getName();
    }

    @hide /** @hide */
    @Override
    public void onInitializeAccessibilityNodeInfoInternal(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfoInternal(info);
        info.setScrollable(mItemCount > 1);
        if (isEnabled()) {
            if (mItemCount > 0 && mSelectedPosition < mItemCount - 1) {
                info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
            }
            if (isEnabled() && mItemCount > 0 && mSelectedPosition > 0) {
                info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
            }
        }
    }

    @hide /** @hide */
    @Override
    public boolean performAccessibilityActionInternal(int action, Bundle arguments) {
        if (super.performAccessibilityActionInternal(action, arguments)) {
            return true;
        }
        switch (action) {
            case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
                if (isEnabled() && mItemCount > 0 && mSelectedPosition < mItemCount - 1) {
                    final int currentChildIndex = mSelectedPosition - mFirstPosition;
                    return scrollToChild(currentChildIndex + 1);
                }
            } return false;
            case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
                if (isEnabled() && mItemCount > 0 && mSelectedPosition > 0) {
                    final int currentChildIndex = mSelectedPosition - mFirstPosition;
                    return scrollToChild(currentChildIndex - 1);
                }
            } return false;
        }
        return false;
    }

    Responsible for fling behavior. Use startUsingVelocity(int) to initiate a fling. Each frame of the fling is handled in run(). A FlingRunnable will keep re-posting itself until the fling is done. /**
     * Responsible for fling behavior. Use {@link #startUsingVelocity(int)} to
     * initiate a fling. Each frame of the fling is handled in {@link #run()}.
     * A FlingRunnable will keep re-posting itself until the fling is done.
     */
    private class FlingRunnable implements Runnable {
        Tracks the decay of a fling scroll
/**
         * Tracks the decay of a fling scroll
         */
        private Scroller mScroller;

        X value reported by mScroller on the previous fling
/**
         * X value reported by mScroller on the previous fling
         */
        private int mLastFlingX;

        public FlingRunnable() {
            mScroller = new Scroller(getContext());
        }

        private void startCommon() {
            // Remove any pending flings
            removeCallbacks(this);
        }
        
        public void startUsingVelocity(int initialVelocity) {
            if (initialVelocity == 0) return;
            
            startCommon();
            
            int initialX = initialVelocity < 0 ? Integer.MAX_VALUE : 0;
            mLastFlingX = initialX;
            mScroller.fling(initialX, 0, initialVelocity, 0,
                    0, Integer.MAX_VALUE, 0, Integer.MAX_VALUE);
            post(this);
        }

        public void startUsingDistance(int distance) {
            if (distance == 0) return;
            
            startCommon();
            
            mLastFlingX = 0;
            mScroller.startScroll(0, 0, -distance, 0, mAnimationDuration);
            post(this);
        }
        
        public void stop(boolean scrollIntoSlots) {
            removeCallbacks(this);
            endFling(scrollIntoSlots);
        }
        
        private void endFling(boolean scrollIntoSlots) {
            /*
             * Force the scroller's status to finished (without setting its
             * position to the end)
             */
            mScroller.forceFinished(true);
            
            if (scrollIntoSlots) scrollIntoSlots();
        }

        @Override
        public void run() {

            if (mItemCount == 0) {
                endFling(true);
                return;
            }

            mShouldStopFling = false;
            
            final Scroller scroller = mScroller;
            boolean more = scroller.computeScrollOffset();
            final int x = scroller.getCurrX();

            // Flip sign to convert finger direction to list items direction
            // (e.g. finger moving down means list is moving towards the top)
            int delta = mLastFlingX - x;

            // Pretend that each frame of a fling scroll is a touch scroll
            if (delta > 0) {
                // Moving towards the left. Use leftmost view as mDownTouchPosition
                mDownTouchPosition = mIsRtl ? (mFirstPosition + getChildCount() - 1) :
                    mFirstPosition;

                // Don't fling more than 1 screen
                delta = Math.min(getWidth() - mPaddingLeft - mPaddingRight - 1, delta);
            } else {
                // Moving towards the right. Use rightmost view as mDownTouchPosition
                int offsetToLast = getChildCount() - 1;
                mDownTouchPosition = mIsRtl ? mFirstPosition :
                    (mFirstPosition + getChildCount() - 1);

                // Don't fling more than 1 screen
                delta = Math.max(-(getWidth() - mPaddingRight - mPaddingLeft - 1), delta);
            }

            trackMotionScroll(delta);

            if (more && !mShouldStopFling) {
                mLastFlingX = x;
                post(this);
            } else {
               endFling(true);
            }
        }
        
    }
    
    Gallery extends LayoutParams to provide a place to hold current
Transformation information along with previous position/transformation
info.
/**
     * Gallery extends LayoutParams to provide a place to hold current
     * Transformation information along with previous position/transformation
     * info.
     */
    public static class LayoutParams extends ViewGroup.LayoutParams {
        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
        }

        public LayoutParams(int w, int h) {
            super(w, h);
        }

        public LayoutParams(ViewGroup.LayoutParams source) {
            super(source);
        }
    }
}
@attr	ref android.R.styleable#Gallery_animationDuration
@attr	ref android.R.styleable#Gallery_spacing
@attr	ref android.R.styleable#Gallery_gravity
Deprecated:	This widget is no longer supported. Other horizontally scrolling widgets include `HorizontalScrollView` and `ViewPager` from the support library.
Params:	shouldCallback – Whether or not to callback on the listener when a item that is not selected is clicked.
@hide
Params:	animationDurationMillis – The duration of the transition, in milliseconds.
@attr	ref android.R.styleable#Gallery_animationDuration
Params:	spacing – The spacing in pixels between items in the Gallery
@attr	ref android.R.styleable#Gallery_spacing
Params:	unselectedAlpha – the alpha for the items that are not selected.
@attr	ref android.R.styleable#Gallery_unselectedAlpha
Params:	position – Position in the gallery for the view to obtain offset – Offset from the selected position x – X-coordinate indicating where this view should be placed. This will either be the left or right edge of the view, depending on the fromLeft parameter fromLeft – Are we positioning views based on the left edge? (i.e., building from left to right)?
Returns:	A view that has been added to the gallery
Params:	child – Child to place
Returns:	Where the top of the child should be
Params:	gravity –
@attr	ref android.R.styleable#Gallery_gravity
/

android/ android-9.0.0_r35/ android/widget/Gallery.java
