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

ScrollView
https://source.android.com/
/*
 * Copyright (C) 2006 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.content.Context;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.os.Build;
import android.os.Build.VERSION_CODES;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.StrictMode;
import android.util.AttributeSet;
import android.util.Log;
import android.view.FocusFinder;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewDebug;
import android.view.ViewGroup;
import android.view.ViewHierarchyEncoder;
import android.view.ViewParent;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;
import android.view.animation.AnimationUtils;

import com.android.internal.R;

import java.util.List;

A view group that allows the view hierarchy placed within it to be scrolled. Scroll view may have only one direct child placed within it. To add multiple views within the scroll view, make the direct child you add a view group, for example LinearLayout, and place additional views within that LinearLayout. Scroll view supports vertical scrolling only. For horizontal scrolling, use HorizontalScrollView instead.
Never add a RecyclerView or ListView to a scroll view. Doing so results in poor user interface performance and a poor user experience.
 For vertical scrolling, consider NestedScrollView instead of scroll view which offers greater user interface flexibility and support for the material design scrolling patterns.
To learn more about material design patterns for handling scrolling, see

Scrolling techniques.
@attr ref android.R.styleable#ScrollView_fillViewport/**
 * A view group that allows the view hierarchy placed within it to be scrolled.
 * Scroll view may have only one direct child placed within it.
 * To add multiple views within the scroll view, make
 * the direct child you add a view group, for example {@link LinearLayout}, and
 * place additional views within that LinearLayout.
 *
 * <p>Scroll view supports vertical scrolling only. For horizontal scrolling,
 * use {@link HorizontalScrollView} instead.</p>
 *
 * <p>Never add a {@link android.support.v7.widget.RecyclerView} or {@link ListView} to
 * a scroll view. Doing so results in poor user interface performance and a poor user
 * experience.</p>
 *
 * <p class="note">
 * For vertical scrolling, consider {@link android.support.v4.widget.NestedScrollView}
 * instead of scroll view which offers greater user interface flexibility and
 * support for the material design scrolling patterns.</p>
 *
 * <p>To learn more about material design patterns for handling scrolling, see
 * <a href="https://material.io/guidelines/patterns/scrolling-techniques.html#">
 * Scrolling techniques</a>.</p>
 *
 * @attr ref android.R.styleable#ScrollView_fillViewport
 */
public class ScrollView extends FrameLayout {
    static final int ANIMATED_SCROLL_GAP = 250;

    static final float MAX_SCROLL_FACTOR = 0.5f;

    private static final String TAG = "ScrollView";

    private long mLastScroll;

    private final Rect mTempRect = new Rect();
    private OverScroller mScroller;
    private EdgeEffect mEdgeGlowTop;
    private EdgeEffect mEdgeGlowBottom;

    Position of the last motion event.
/**
     * Position of the last motion event.
     */
    private int mLastMotionY;

    True when the layout has changed but the traversal has not come through yet.
Ideally the view hierarchy would keep track of this for us.
/**
     * True when the layout has changed but the traversal has not come through yet.
     * Ideally the view hierarchy would keep track of this for us.
     */
    private boolean mIsLayoutDirty = true;

    The child to give focus to in the event that a child has requested focus while the
layout is dirty. This prevents the scroll from being wrong if the child has not been
laid out before requesting focus.
/**
     * The child to give focus to in the event that a child has requested focus while the
     * layout is dirty. This prevents the scroll from being wrong if the child has not been
     * laid out before requesting focus.
     */
    private View mChildToScrollTo = null;

    True if the user is currently dragging this ScrollView around. This is
not the same as 'is being flinged', which can be checked by
mScroller.isFinished() (flinging begins when the user lifts his finger).
/**
     * True if the user is currently dragging this ScrollView around. This is
     * not the same as 'is being flinged', which can be checked by
     * mScroller.isFinished() (flinging begins when the user lifts his finger).
     */
    private boolean mIsBeingDragged = false;

    Determines speed during touch scrolling
/**
     * Determines speed during touch scrolling
     */
    private VelocityTracker mVelocityTracker;

    When set to true, the scroll view measure its child to make it fill the currently
visible area.
/**
     * When set to true, the scroll view measure its child to make it fill the currently
     * visible area.
     */
    @ViewDebug.ExportedProperty(category = "layout")
    private boolean mFillViewport;

    Whether arrow scrolling is animated.
/**
     * Whether arrow scrolling is animated.
     */
    private boolean mSmoothScrollingEnabled = true;

    private int mTouchSlop;
    private int mMinimumVelocity;
    private int mMaximumVelocity;

    private int mOverscrollDistance;
    private int mOverflingDistance;

    private float mVerticalScrollFactor;

    ID of the active pointer. This is used to retain consistency during
drags/flings if multiple pointers are used.
/**
     * ID of the active pointer. This is used to retain consistency during
     * drags/flings if multiple pointers are used.
     */
    private int mActivePointerId = INVALID_POINTER;

    Used during scrolling to retrieve the new offset within the window.
/**
     * Used during scrolling to retrieve the new offset within the window.
     */
    private final int[] mScrollOffset = new int[2];
    private final int[] mScrollConsumed = new int[2];
    private int mNestedYOffset;

    The StrictMode "critical time span" objects to catch animation
stutters.  Non-null when a time-sensitive animation is
in-flight.  Must call finish() on them when done animating.
These are no-ops on user builds.
/**
     * The StrictMode "critical time span" objects to catch animation
     * stutters.  Non-null when a time-sensitive animation is
     * in-flight.  Must call finish() on them when done animating.
     * These are no-ops on user builds.
     */
    private StrictMode.Span mScrollStrictSpan = null;  // aka "drag"
    private StrictMode.Span mFlingStrictSpan = null;

    Sentinel value for no current active pointer. Used by mActivePointerId. /**
     * Sentinel value for no current active pointer.
     * Used by {@link #mActivePointerId}.
     */
    private static final int INVALID_POINTER = -1;

    private SavedState mSavedState;

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

    public ScrollView(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.scrollViewStyle);
    }

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

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

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

        setFillViewport(a.getBoolean(R.styleable.ScrollView_fillViewport, false));

        a.recycle();

        if (context.getResources().getConfiguration().uiMode == Configuration.UI_MODE_TYPE_WATCH) {
            setRevealOnFocusHint(false);
        }
    }

    @Override
    public boolean shouldDelayChildPressedState() {
        return true;
    }

    @Override
    protected float getTopFadingEdgeStrength() {
        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getVerticalFadingEdgeLength();
        if (mScrollY < length) {
            return mScrollY / (float) length;
        }

        return 1.0f;
    }

    @Override
    protected float getBottomFadingEdgeStrength() {
        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getVerticalFadingEdgeLength();
        final int bottomEdge = getHeight() - mPaddingBottom;
        final int span = getChildAt(0).getBottom() - mScrollY - bottomEdge;
        if (span < length) {
            return span / (float) length;
        }

        return 1.0f;
    }

    Returns: The maximum amount this scroll view will scroll in response to
  an arrow event./**
     * @return The maximum amount this scroll view will scroll in response to
     *   an arrow event.
     */
    public int getMaxScrollAmount() {
        return (int) (MAX_SCROLL_FACTOR * (mBottom - mTop));
    }


    private void initScrollView() {
        mScroller = new OverScroller(getContext());
        setFocusable(true);
        setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
        setWillNotDraw(false);
        final ViewConfiguration configuration = ViewConfiguration.get(mContext);
        mTouchSlop = configuration.getScaledTouchSlop();
        mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
        mOverscrollDistance = configuration.getScaledOverscrollDistance();
        mOverflingDistance = configuration.getScaledOverflingDistance();
        mVerticalScrollFactor = configuration.getScaledVerticalScrollFactor();
    }

    @Override
    public void addView(View child) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child);
    }

    @Override
    public void addView(View child, int index) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, index);
    }

    @Override
    public void addView(View child, ViewGroup.LayoutParams params) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, params);
    }

    @Override
    public void addView(View child, int index, ViewGroup.LayoutParams params) {
        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, index, params);
    }

    Returns: Returns true this ScrollView can be scrolled/**
     * @return Returns true this ScrollView can be scrolled
     */
    private boolean canScroll() {
        View child = getChildAt(0);
        if (child != null) {
            int childHeight = child.getHeight();
            return getHeight() < childHeight + mPaddingTop + mPaddingBottom;
        }
        return false;
    }

    Indicates whether this ScrollView's content is stretched to fill the viewport.
Returns: True if the content fills the viewport, false otherwise.
@attr ref android.R.styleable#ScrollView_fillViewport/**
     * Indicates whether this ScrollView's content is stretched to fill the viewport.
     *
     * @return True if the content fills the viewport, false otherwise.
     *
     * @attr ref android.R.styleable#ScrollView_fillViewport
     */
    public boolean isFillViewport() {
        return mFillViewport;
    }

    Indicates this ScrollView whether it should stretch its content height to fill
the viewport or not.
Params: fillViewport – True to stretch the content's height to the viewport's
       boundaries, false otherwise.
@attr ref android.R.styleable#ScrollView_fillViewport/**
     * Indicates this ScrollView whether it should stretch its content height to fill
     * the viewport or not.
     *
     * @param fillViewport True to stretch the content's height to the viewport's
     *        boundaries, false otherwise.
     *
     * @attr ref android.R.styleable#ScrollView_fillViewport
     */
    public void setFillViewport(boolean fillViewport) {
        if (fillViewport != mFillViewport) {
            mFillViewport = fillViewport;
            requestLayout();
        }
    }

    Returns: Whether arrow scrolling will animate its transition./**
     * @return Whether arrow scrolling will animate its transition.
     */
    public boolean isSmoothScrollingEnabled() {
        return mSmoothScrollingEnabled;
    }

    Set whether arrow scrolling will animate its transition.
Params: smoothScrollingEnabled – whether arrow scrolling will animate its transition/**
     * Set whether arrow scrolling will animate its transition.
     * @param smoothScrollingEnabled whether arrow scrolling will animate its transition
     */
    public void setSmoothScrollingEnabled(boolean smoothScrollingEnabled) {
        mSmoothScrollingEnabled = smoothScrollingEnabled;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        if (!mFillViewport) {
            return;
        }

        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightMode == MeasureSpec.UNSPECIFIED) {
            return;
        }

        if (getChildCount() > 0) {
            final View child = getChildAt(0);
            final int widthPadding;
            final int heightPadding;
            final int targetSdkVersion = getContext().getApplicationInfo().targetSdkVersion;
            final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();
            if (targetSdkVersion >= VERSION_CODES.M) {
                widthPadding = mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin;
                heightPadding = mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin;
            } else {
                widthPadding = mPaddingLeft + mPaddingRight;
                heightPadding = mPaddingTop + mPaddingBottom;
            }

            final int desiredHeight = getMeasuredHeight() - heightPadding;
            if (child.getMeasuredHeight() < desiredHeight) {
                final int childWidthMeasureSpec = getChildMeasureSpec(
                        widthMeasureSpec, widthPadding, lp.width);
                final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                        desiredHeight, MeasureSpec.EXACTLY);
                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
            }
        }
    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        // Let the focused view and/or our descendants get the key first
        return super.dispatchKeyEvent(event) || executeKeyEvent(event);
    }

    You can call this function yourself to have the scroll view perform
scrolling from a key event, just as if the event had been dispatched to
it by the view hierarchy.
Params: event – The key event to execute.
Returns: Return true if the event was handled, else false./**
     * You can call this function yourself to have the scroll view perform
     * scrolling from a key event, just as if the event had been dispatched to
     * it by the view hierarchy.
     *
     * @param event The key event to execute.
     * @return Return true if the event was handled, else false.
     */
    public boolean executeKeyEvent(KeyEvent event) {
        mTempRect.setEmpty();

        if (!canScroll()) {
            if (isFocused() && event.getKeyCode() != KeyEvent.KEYCODE_BACK) {
                View currentFocused = findFocus();
                if (currentFocused == this) currentFocused = null;
                View nextFocused = FocusFinder.getInstance().findNextFocus(this,
                        currentFocused, View.FOCUS_DOWN);
                return nextFocused != null
                        && nextFocused != this
                        && nextFocused.requestFocus(View.FOCUS_DOWN);
            }
            return false;
        }

        boolean handled = false;
        if (event.getAction() == KeyEvent.ACTION_DOWN) {
            switch (event.getKeyCode()) {
                case KeyEvent.KEYCODE_DPAD_UP:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_UP);
                    } else {
                        handled = fullScroll(View.FOCUS_UP);
                    }
                    break;
                case KeyEvent.KEYCODE_DPAD_DOWN:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_DOWN);
                    } else {
                        handled = fullScroll(View.FOCUS_DOWN);
                    }
                    break;
                case KeyEvent.KEYCODE_SPACE:
                    pageScroll(event.isShiftPressed() ? View.FOCUS_UP : View.FOCUS_DOWN);
                    break;
            }
        }

        return handled;
    }

    private boolean inChild(int x, int y) {
        if (getChildCount() > 0) {
            final int scrollY = mScrollY;
            final View child = getChildAt(0);
            return !(y < child.getTop() - scrollY
                    || y >= child.getBottom() - scrollY
                    || x < child.getLeft()
                    || x >= child.getRight());
        }
        return false;
    }

    private void initOrResetVelocityTracker() {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        } else {
            mVelocityTracker.clear();
        }
    }

    private void initVelocityTrackerIfNotExists() {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
    }

    private void recycleVelocityTracker() {
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        if (disallowIntercept) {
            recycleVelocityTracker();
        }
        super.requestDisallowInterceptTouchEvent(disallowIntercept);
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onMotionEvent will be called and we do the actual
         * scrolling there.
         */

        /*
        * Shortcut the most recurring case: the user is in the dragging
        * state and he is moving his finger.  We want to intercept this
        * motion.
        */
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged)) {
            return true;
        }

        if (super.onInterceptTouchEvent(ev)) {
            return true;
        }

        /*
         * Don't try to intercept touch if we can't scroll anyway.
         */
        if (getScrollY() == 0 && !canScrollVertically(1)) {
            return false;
        }

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_MOVE: {
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */

                /*
                * Locally do absolute value. mLastMotionY is set to the y value
                * of the down event.
                */
                final int activePointerId = mActivePointerId;
                if (activePointerId == INVALID_POINTER) {
                    // If we don't have a valid id, the touch down wasn't on content.
                    break;
                }

                final int pointerIndex = ev.findPointerIndex(activePointerId);
                if (pointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=" + activePointerId
                            + " in onInterceptTouchEvent");
                    break;
                }

                final int y = (int) ev.getY(pointerIndex);
                final int yDiff = Math.abs(y - mLastMotionY);
                if (yDiff > mTouchSlop && (getNestedScrollAxes() & SCROLL_AXIS_VERTICAL) == 0) {
                    mIsBeingDragged = true;
                    mLastMotionY = y;
                    initVelocityTrackerIfNotExists();
                    mVelocityTracker.addMovement(ev);
                    mNestedYOffset = 0;
                    if (mScrollStrictSpan == null) {
                        mScrollStrictSpan = StrictMode.enterCriticalSpan("ScrollView-scroll");
                    }
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {
                final int y = (int) ev.getY();
                if (!inChild((int) ev.getX(), (int) y)) {
                    mIsBeingDragged = false;
                    recycleVelocityTracker();
                    break;
                }

                /*
                 * Remember location of down touch.
                 * ACTION_DOWN always refers to pointer index 0.
                 */
                mLastMotionY = y;
                mActivePointerId = ev.getPointerId(0);

                initOrResetVelocityTracker();
                mVelocityTracker.addMovement(ev);
                /*
                 * If being flinged and user touches the screen, initiate drag;
                 * otherwise don't. mScroller.isFinished should be false when
                 * being flinged. We need to call computeScrollOffset() first so that
                 * isFinished() is correct.
                */
                mScroller.computeScrollOffset();
                mIsBeingDragged = !mScroller.isFinished();
                if (mIsBeingDragged && mScrollStrictSpan == null) {
                    mScrollStrictSpan = StrictMode.enterCriticalSpan("ScrollView-scroll");
                }
                startNestedScroll(SCROLL_AXIS_VERTICAL);
                break;
            }

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                recycleVelocityTracker();
                if (mScroller.springBack(mScrollX, mScrollY, 0, 0, 0, getScrollRange())) {
                    postInvalidateOnAnimation();
                }
                stopNestedScroll();
                break;
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;
        }

        /*
        * The only time we want to intercept motion events is if we are in the
        * drag mode.
        */
        return mIsBeingDragged;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        initVelocityTrackerIfNotExists();

        MotionEvent vtev = MotionEvent.obtain(ev);

        final int actionMasked = ev.getActionMasked();

        if (actionMasked == MotionEvent.ACTION_DOWN) {
            mNestedYOffset = 0;
        }
        vtev.offsetLocation(0, mNestedYOffset);

        switch (actionMasked) {
            case MotionEvent.ACTION_DOWN: {
                if (getChildCount() == 0) {
                    return false;
                }
                if ((mIsBeingDragged = !mScroller.isFinished())) {
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                }

                /*
                 * If being flinged and user touches, stop the fling. isFinished
                 * will be false if being flinged.
                 */
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                    if (mFlingStrictSpan != null) {
                        mFlingStrictSpan.finish();
                        mFlingStrictSpan = null;
                    }
                }

                // Remember where the motion event started
                mLastMotionY = (int) ev.getY();
                mActivePointerId = ev.getPointerId(0);
                startNestedScroll(SCROLL_AXIS_VERTICAL);
                break;
            }
            case MotionEvent.ACTION_MOVE:
                final int activePointerIndex = ev.findPointerIndex(mActivePointerId);
                if (activePointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=" + mActivePointerId + " in onTouchEvent");
                    break;
                }

                final int y = (int) ev.getY(activePointerIndex);
                int deltaY = mLastMotionY - y;
                if (dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
                    deltaY -= mScrollConsumed[1];
                    vtev.offsetLocation(0, mScrollOffset[1]);
                    mNestedYOffset += mScrollOffset[1];
                }
                if (!mIsBeingDragged && Math.abs(deltaY) > mTouchSlop) {
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                    mIsBeingDragged = true;
                    if (deltaY > 0) {
                        deltaY -= mTouchSlop;
                    } else {
                        deltaY += mTouchSlop;
                    }
                }
                if (mIsBeingDragged) {
                    // Scroll to follow the motion event
                    mLastMotionY = y - mScrollOffset[1];

                    final int oldY = mScrollY;
                    final int range = getScrollRange();
                    final int overscrollMode = getOverScrollMode();
                    boolean canOverscroll = overscrollMode == OVER_SCROLL_ALWAYS ||
                            (overscrollMode == OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);

                    // Calling overScrollBy will call onOverScrolled, which
                    // calls onScrollChanged if applicable.
                    if (overScrollBy(0, deltaY, 0, mScrollY, 0, range, 0, mOverscrollDistance, true)
                            && !hasNestedScrollingParent()) {
                        // Break our velocity if we hit a scroll barrier.
                        mVelocityTracker.clear();
                    }

                    final int scrolledDeltaY = mScrollY - oldY;
                    final int unconsumedY = deltaY - scrolledDeltaY;
                    if (dispatchNestedScroll(0, scrolledDeltaY, 0, unconsumedY, mScrollOffset)) {
                        mLastMotionY -= mScrollOffset[1];
                        vtev.offsetLocation(0, mScrollOffset[1]);
                        mNestedYOffset += mScrollOffset[1];
                    } else if (canOverscroll) {
                        final int pulledToY = oldY + deltaY;
                        if (pulledToY < 0) {
                            mEdgeGlowTop.onPull((float) deltaY / getHeight(),
                                    ev.getX(activePointerIndex) / getWidth());
                            if (!mEdgeGlowBottom.isFinished()) {
                                mEdgeGlowBottom.onRelease();
                            }
                        } else if (pulledToY > range) {
                            mEdgeGlowBottom.onPull((float) deltaY / getHeight(),
                                    1.f - ev.getX(activePointerIndex) / getWidth());
                            if (!mEdgeGlowTop.isFinished()) {
                                mEdgeGlowTop.onRelease();
                            }
                        }
                        if (mEdgeGlowTop != null
                                && (!mEdgeGlowTop.isFinished() || !mEdgeGlowBottom.isFinished())) {
                            postInvalidateOnAnimation();
                        }
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                if (mIsBeingDragged) {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                    int initialVelocity = (int) velocityTracker.getYVelocity(mActivePointerId);

                    if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
                        flingWithNestedDispatch(-initialVelocity);
                    } else if (mScroller.springBack(mScrollX, mScrollY, 0, 0, 0,
                            getScrollRange())) {
                        postInvalidateOnAnimation();
                    }

                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                if (mIsBeingDragged && getChildCount() > 0) {
                    if (mScroller.springBack(mScrollX, mScrollY, 0, 0, 0, getScrollRange())) {
                        postInvalidateOnAnimation();
                    }
                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEvent.ACTION_POINTER_DOWN: {
                final int index = ev.getActionIndex();
                mLastMotionY = (int) ev.getY(index);
                mActivePointerId = ev.getPointerId(index);
                break;
            }
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                mLastMotionY = (int) ev.getY(ev.findPointerIndex(mActivePointerId));
                break;
        }

        if (mVelocityTracker != null) {
            mVelocityTracker.addMovement(vtev);
        }
        vtev.recycle();
        return true;
    }

    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                MotionEvent.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = ev.getPointerId(pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            // TODO: Make this decision more intelligent.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mLastMotionY = (int) ev.getY(newPointerIndex);
            mActivePointerId = ev.getPointerId(newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }

    @Override
    public boolean onGenericMotionEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_SCROLL:
                final float axisValue;
                if (event.isFromSource(InputDevice.SOURCE_CLASS_POINTER)) {
                    axisValue = event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                } else if (event.isFromSource(InputDevice.SOURCE_ROTARY_ENCODER)) {
                    axisValue = event.getAxisValue(MotionEvent.AXIS_SCROLL);
                } else {
                    axisValue = 0;
                }

                final int delta = Math.round(axisValue * mVerticalScrollFactor);
                if (delta != 0) {
                    final int range = getScrollRange();
                    int oldScrollY = mScrollY;
                    int newScrollY = oldScrollY - delta;
                    if (newScrollY < 0) {
                        newScrollY = 0;
                    } else if (newScrollY > range) {
                        newScrollY = range;
                    }
                    if (newScrollY != oldScrollY) {
                        super.scrollTo(mScrollX, newScrollY);
                        return true;
                    }
                }
                break;
        }

        return super.onGenericMotionEvent(event);
    }

    @Override
    protected void onOverScrolled(int scrollX, int scrollY,
            boolean clampedX, boolean clampedY) {
        // Treat animating scrolls differently; see #computeScroll() for why.
        if (!mScroller.isFinished()) {
            final int oldX = mScrollX;
            final int oldY = mScrollY;
            mScrollX = scrollX;
            mScrollY = scrollY;
            invalidateParentIfNeeded();
            onScrollChanged(mScrollX, mScrollY, oldX, oldY);
            if (clampedY) {
                mScroller.springBack(mScrollX, mScrollY, 0, 0, 0, getScrollRange());
            }
        } else {
            super.scrollTo(scrollX, scrollY);
        }

        awakenScrollBars();
    }

    @hide /** @hide */
    @Override
    public boolean performAccessibilityActionInternal(int action, Bundle arguments) {
        if (super.performAccessibilityActionInternal(action, arguments)) {
            return true;
        }
        if (!isEnabled()) {
            return false;
        }
        switch (action) {
            case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD:
            case R.id.accessibilityActionScrollDown: {
                final int viewportHeight = getHeight() - mPaddingBottom - mPaddingTop;
                final int targetScrollY = Math.min(mScrollY + viewportHeight, getScrollRange());
                if (targetScrollY != mScrollY) {
                    smoothScrollTo(0, targetScrollY);
                    return true;
                }
            } return false;
            case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD:
            case R.id.accessibilityActionScrollUp: {
                final int viewportHeight = getHeight() - mPaddingBottom - mPaddingTop;
                final int targetScrollY = Math.max(mScrollY - viewportHeight, 0);
                if (targetScrollY != mScrollY) {
                    smoothScrollTo(0, targetScrollY);
                    return true;
                }
            } return false;
        }
        return false;
    }

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

    @hide /** @hide */
    @Override
    public void onInitializeAccessibilityNodeInfoInternal(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfoInternal(info);
        if (isEnabled()) {
            final int scrollRange = getScrollRange();
            if (scrollRange > 0) {
                info.setScrollable(true);
                if (mScrollY > 0) {
                    info.addAction(
                            AccessibilityNodeInfo.AccessibilityAction.ACTION_SCROLL_BACKWARD);
                    info.addAction(AccessibilityNodeInfo.AccessibilityAction.ACTION_SCROLL_UP);
                }
                if (mScrollY < scrollRange) {
                    info.addAction(AccessibilityNodeInfo.AccessibilityAction.ACTION_SCROLL_FORWARD);
                    info.addAction(AccessibilityNodeInfo.AccessibilityAction.ACTION_SCROLL_DOWN);
                }
            }
        }
    }

    @hide /** @hide */
    @Override
    public void onInitializeAccessibilityEventInternal(AccessibilityEvent event) {
        super.onInitializeAccessibilityEventInternal(event);
        final boolean scrollable = getScrollRange() > 0;
        event.setScrollable(scrollable);
        event.setScrollX(mScrollX);
        event.setScrollY(mScrollY);
        event.setMaxScrollX(mScrollX);
        event.setMaxScrollY(getScrollRange());
    }

    private int getScrollRange() {
        int scrollRange = 0;
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            scrollRange = Math.max(0,
                    child.getHeight() - (getHeight() - mPaddingBottom - mPaddingTop));
        }
        return scrollRange;
    }

    
Finds the next focusable component that fits in the specified bounds.

Params: topFocus – look for a candidate is the one at the top of the bounds
                if topFocus is true, or at the bottom of the bounds if topFocus is
                false
top –      the top offset of the bounds in which a focusable must be
                found
bottom –   the bottom offset of the bounds in which a focusable must
                be found
Returns: the next focusable component in the bounds or null if none can
        be found/**
     * <p>
     * Finds the next focusable component that fits in the specified bounds.
     * </p>
     *
     * @param topFocus look for a candidate is the one at the top of the bounds
     *                 if topFocus is true, or at the bottom of the bounds if topFocus is
     *                 false
     * @param top      the top offset of the bounds in which a focusable must be
     *                 found
     * @param bottom   the bottom offset of the bounds in which a focusable must
     *                 be found
     * @return the next focusable component in the bounds or null if none can
     *         be found
     */
    private View findFocusableViewInBounds(boolean topFocus, int top, int bottom) {

        List<View> focusables = getFocusables(View.FOCUS_FORWARD);
        View focusCandidate = null;

        /*
         * A fully contained focusable is one where its top is below the bound's
         * top, and its bottom is above the bound's bottom. A partially
         * contained focusable is one where some part of it is within the
         * bounds, but it also has some part that is not within bounds.  A fully contained
         * focusable is preferred to a partially contained focusable.
         */
        boolean foundFullyContainedFocusable = false;

        int count = focusables.size();
        for (int i = 0; i < count; i++) {
            View view = focusables.get(i);
            int viewTop = view.getTop();
            int viewBottom = view.getBottom();

            if (top < viewBottom && viewTop < bottom) {
                /*
                 * the focusable is in the target area, it is a candidate for
                 * focusing
                 */

                final boolean viewIsFullyContained = (top < viewTop) &&
                        (viewBottom < bottom);

                if (focusCandidate == null) {
                    /* No candidate, take this one */
                    focusCandidate = view;
                    foundFullyContainedFocusable = viewIsFullyContained;
                } else {
                    final boolean viewIsCloserToBoundary =
                            (topFocus && viewTop < focusCandidate.getTop()) ||
                                    (!topFocus && viewBottom > focusCandidate
                                            .getBottom());

                    if (foundFullyContainedFocusable) {
                        if (viewIsFullyContained && viewIsCloserToBoundary) {
                            /*
                             * We're dealing with only fully contained views, so
                             * it has to be closer to the boundary to beat our
                             * candidate
                             */
                            focusCandidate = view;
                        }
                    } else {
                        if (viewIsFullyContained) {
                            /* Any fully contained view beats a partially contained view */
                            focusCandidate = view;
                            foundFullyContainedFocusable = true;
                        } else if (viewIsCloserToBoundary) {
                            /*
                             * Partially contained view beats another partially
                             * contained view if it's closer
                             */
                            focusCandidate = view;
                        }
                    }
                }
            }
        }

        return focusCandidate;
    }

    Handles scrolling in response to a "page up/down" shortcut press. This
method will scroll the view by one page up or down and give the focus
to the topmost/bottommost component in the new visible area. If no
component is a good candidate for focus, this scrollview reclaims the
focus.
Params: direction – the scroll direction: View.FOCUS_UP to go one page up or View.FOCUS_DOWN to go one page down
Returns: true if the key event is consumed by this method, false otherwise/**
     * <p>Handles scrolling in response to a "page up/down" shortcut press. This
     * method will scroll the view by one page up or down and give the focus
     * to the topmost/bottommost component in the new visible area. If no
     * component is a good candidate for focus, this scrollview reclaims the
     * focus.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_UP}
     *                  to go one page up or
     *                  {@link android.view.View#FOCUS_DOWN} to go one page down
     * @return true if the key event is consumed by this method, false otherwise
     */
    public boolean pageScroll(int direction) {
        boolean down = direction == View.FOCUS_DOWN;
        int height = getHeight();

        if (down) {
            mTempRect.top = getScrollY() + height;
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(count - 1);
                if (mTempRect.top + height > view.getBottom()) {
                    mTempRect.top = view.getBottom() - height;
                }
            }
        } else {
            mTempRect.top = getScrollY() - height;
            if (mTempRect.top < 0) {
                mTempRect.top = 0;
            }
        }
        mTempRect.bottom = mTempRect.top + height;

        return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
    }

    Handles scrolling in response to a "home/end" shortcut press. This
method will scroll the view to the top or bottom and give the focus
to the topmost/bottommost component in the new visible area. If no
component is a good candidate for focus, this scrollview reclaims the
focus.
Params: direction – the scroll direction: View.FOCUS_UP to go the top of the view or View.FOCUS_DOWN to go the bottom
Returns: true if the key event is consumed by this method, false otherwise/**
     * <p>Handles scrolling in response to a "home/end" shortcut press. This
     * method will scroll the view to the top or bottom and give the focus
     * to the topmost/bottommost component in the new visible area. If no
     * component is a good candidate for focus, this scrollview reclaims the
     * focus.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_UP}
     *                  to go the top of the view or
     *                  {@link android.view.View#FOCUS_DOWN} to go the bottom
     * @return true if the key event is consumed by this method, false otherwise
     */
    public boolean fullScroll(int direction) {
        boolean down = direction == View.FOCUS_DOWN;
        int height = getHeight();

        mTempRect.top = 0;
        mTempRect.bottom = height;

        if (down) {
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(count - 1);
                mTempRect.bottom = view.getBottom() + mPaddingBottom;
                mTempRect.top = mTempRect.bottom - height;
            }
        }

        return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
    }

    Scrolls the view to make the area defined by top and
bottom visible. This method attempts to give the focus
to a component visible in this area. If no component can be focused in
the new visible area, the focus is reclaimed by this ScrollView.
Params: direction – the scroll direction: View.FOCUS_UP to go upward, View.FOCUS_DOWN to downward
top –       the top offset of the new area to be made visible
bottom –    the bottom offset of the new area to be made visible
Returns: true if the key event is consumed by this method, false otherwise/**
     * <p>Scrolls the view to make the area defined by <code>top</code> and
     * <code>bottom</code> visible. This method attempts to give the focus
     * to a component visible in this area. If no component can be focused in
     * the new visible area, the focus is reclaimed by this ScrollView.</p>
     *
     * @param direction the scroll direction: {@link android.view.View#FOCUS_UP}
     *                  to go upward, {@link android.view.View#FOCUS_DOWN} to downward
     * @param top       the top offset of the new area to be made visible
     * @param bottom    the bottom offset of the new area to be made visible
     * @return true if the key event is consumed by this method, false otherwise
     */
    private boolean scrollAndFocus(int direction, int top, int bottom) {
        boolean handled = true;

        int height = getHeight();
        int containerTop = getScrollY();
        int containerBottom = containerTop + height;
        boolean up = direction == View.FOCUS_UP;

        View newFocused = findFocusableViewInBounds(up, top, bottom);
        if (newFocused == null) {
            newFocused = this;
        }

        if (top >= containerTop && bottom <= containerBottom) {
            handled = false;
        } else {
            int delta = up ? (top - containerTop) : (bottom - containerBottom);
            doScrollY(delta);
        }

        if (newFocused != findFocus()) newFocused.requestFocus(direction);

        return handled;
    }

    Handle scrolling in response to an up or down arrow click.
Params: direction – The direction corresponding to the arrow key that was
                 pressed
Returns: True if we consumed the event, false otherwise/**
     * Handle scrolling in response to an up or down arrow click.
     *
     * @param direction The direction corresponding to the arrow key that was
     *                  pressed
     * @return True if we consumed the event, false otherwise
     */
    public boolean arrowScroll(int direction) {

        View currentFocused = findFocus();
        if (currentFocused == this) currentFocused = null;

        View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);

        final int maxJump = getMaxScrollAmount();

        if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump, getHeight())) {
            nextFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(nextFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollY(scrollDelta);
            nextFocused.requestFocus(direction);
        } else {
            // no new focus
            int scrollDelta = maxJump;

            if (direction == View.FOCUS_UP && getScrollY() < scrollDelta) {
                scrollDelta = getScrollY();
            } else if (direction == View.FOCUS_DOWN) {
                if (getChildCount() > 0) {
                    int daBottom = getChildAt(0).getBottom();
                    int screenBottom = getScrollY() + getHeight() - mPaddingBottom;
                    if (daBottom - screenBottom < maxJump) {
                        scrollDelta = daBottom - screenBottom;
                    }
                }
            }
            if (scrollDelta == 0) {
                return false;
            }
            doScrollY(direction == View.FOCUS_DOWN ? scrollDelta : -scrollDelta);
        }

        if (currentFocused != null && currentFocused.isFocused()
                && isOffScreen(currentFocused)) {
            // previously focused item still has focus and is off screen, give
            // it up (take it back to ourselves)
            // (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we are
            // sure to
            // get it)
            final int descendantFocusability = getDescendantFocusability();  // save
            setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
            requestFocus();
            setDescendantFocusability(descendantFocusability);  // restore
        }
        return true;
    }

    Returns: whether the descendant of this scroll view is scrolled off
 screen./**
     * @return whether the descendant of this scroll view is scrolled off
     *  screen.
     */
    private boolean isOffScreen(View descendant) {
        return !isWithinDeltaOfScreen(descendant, 0, getHeight());
    }

    Returns: whether the descendant of this scroll view is within delta
 pixels of being on the screen./**
     * @return whether the descendant of this scroll view is within delta
     *  pixels of being on the screen.
     */
    private boolean isWithinDeltaOfScreen(View descendant, int delta, int height) {
        descendant.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(descendant, mTempRect);

        return (mTempRect.bottom + delta) >= getScrollY()
                && (mTempRect.top - delta) <= (getScrollY() + height);
    }

    Smooth scroll by a Y delta
Params: delta – the number of pixels to scroll by on the Y axis/**
     * Smooth scroll by a Y delta
     *
     * @param delta the number of pixels to scroll by on the Y axis
     */
    private void doScrollY(int delta) {
        if (delta != 0) {
            if (mSmoothScrollingEnabled) {
                smoothScrollBy(0, delta);
            } else {
                scrollBy(0, delta);
            }
        }
    }

    Like View.scrollBy, but scroll smoothly instead of immediately. 
Params: dx – the number of pixels to scroll by on the X axis
dy – the number of pixels to scroll by on the Y axis/**
     * Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
     *
     * @param dx the number of pixels to scroll by on the X axis
     * @param dy the number of pixels to scroll by on the Y axis
     */
    public final void smoothScrollBy(int dx, int dy) {
        if (getChildCount() == 0) {
            // Nothing to do.
            return;
        }
        long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
        if (duration > ANIMATED_SCROLL_GAP) {
            final int height = getHeight() - mPaddingBottom - mPaddingTop;
            final int bottom = getChildAt(0).getHeight();
            final int maxY = Math.max(0, bottom - height);
            final int scrollY = mScrollY;
            dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;

            mScroller.startScroll(mScrollX, scrollY, 0, dy);
            postInvalidateOnAnimation();
        } else {
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
                if (mFlingStrictSpan != null) {
                    mFlingStrictSpan.finish();
                    mFlingStrictSpan = null;
                }
            }
            scrollBy(dx, dy);
        }
        mLastScroll = AnimationUtils.currentAnimationTimeMillis();
    }

    Like scrollTo, but scroll smoothly instead of immediately. 
Params: x – the position where to scroll on the X axis
y – the position where to scroll on the Y axis/**
     * Like {@link #scrollTo}, but scroll smoothly instead of immediately.
     *
     * @param x the position where to scroll on the X axis
     * @param y the position where to scroll on the Y axis
     */
    public final void smoothScrollTo(int x, int y) {
        smoothScrollBy(x - mScrollX, y - mScrollY);
    }

    The scroll range of a scroll view is the overall height of all of its
children.
/**
     * <p>The scroll range of a scroll view is the overall height of all of its
     * children.</p>
     */
    @Override
    protected int computeVerticalScrollRange() {
        final int count = getChildCount();
        final int contentHeight = getHeight() - mPaddingBottom - mPaddingTop;
        if (count == 0) {
            return contentHeight;
        }

        int scrollRange = getChildAt(0).getBottom();
        final int scrollY = mScrollY;
        final int overscrollBottom = Math.max(0, scrollRange - contentHeight);
        if (scrollY < 0) {
            scrollRange -= scrollY;
        } else if (scrollY > overscrollBottom) {
            scrollRange += scrollY - overscrollBottom;
        }

        return scrollRange;
    }

    @Override
    protected int computeVerticalScrollOffset() {
        return Math.max(0, super.computeVerticalScrollOffset());
    }

    @Override
    protected void measureChild(View child, int parentWidthMeasureSpec,
            int parentHeightMeasureSpec) {
        ViewGroup.LayoutParams lp = child.getLayoutParams();

        int childWidthMeasureSpec;
        int childHeightMeasureSpec;

        childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, mPaddingLeft
                + mPaddingRight, lp.width);
        final int verticalPadding = mPaddingTop + mPaddingBottom;
        childHeightMeasureSpec = MeasureSpec.makeSafeMeasureSpec(
                Math.max(0, MeasureSpec.getSize(parentHeightMeasureSpec) - verticalPadding),
                MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

    @Override
    protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed,
            int parentHeightMeasureSpec, int heightUsed) {
        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
                        + widthUsed, lp.width);
        final int usedTotal = mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin +
                heightUsed;
        final int childHeightMeasureSpec = MeasureSpec.makeSafeMeasureSpec(
                Math.max(0, MeasureSpec.getSize(parentHeightMeasureSpec) - usedTotal),
                MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            // This is called at drawing time by ViewGroup.  We don't want to
            // re-show the scrollbars at this point, which scrollTo will do,
            // so we replicate most of scrollTo here.
            //
            //         It's a little odd to call onScrollChanged from inside the drawing.
            //
            //         It is, except when you remember that computeScroll() is used to
            //         animate scrolling. So unless we want to defer the onScrollChanged()
            //         until the end of the animated scrolling, we don't really have a
            //         choice here.
            //
            //         I agree.  The alternative, which I think would be worse, is to post
            //         something and tell the subclasses later.  This is bad because there
            //         will be a window where mScrollX/Y is different from what the app
            //         thinks it is.
            //
            int oldX = mScrollX;
            int oldY = mScrollY;
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();

            if (oldX != x || oldY != y) {
                final int range = getScrollRange();
                final int overscrollMode = getOverScrollMode();
                final boolean canOverscroll = overscrollMode == OVER_SCROLL_ALWAYS ||
                        (overscrollMode == OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);

                overScrollBy(x - oldX, y - oldY, oldX, oldY, 0, range,
                        0, mOverflingDistance, false);
                onScrollChanged(mScrollX, mScrollY, oldX, oldY);

                if (canOverscroll) {
                    if (y < 0 && oldY >= 0) {
                        mEdgeGlowTop.onAbsorb((int) mScroller.getCurrVelocity());
                    } else if (y > range && oldY <= range) {
                        mEdgeGlowBottom.onAbsorb((int) mScroller.getCurrVelocity());
                    }
                }
            }

            if (!awakenScrollBars()) {
                // Keep on drawing until the animation has finished.
                postInvalidateOnAnimation();
            }
        } else {
            if (mFlingStrictSpan != null) {
                mFlingStrictSpan.finish();
                mFlingStrictSpan = null;
            }
        }
    }

    Scrolls the view to the given child.
Params: child – the View to scroll to/**
     * Scrolls the view to the given child.
     *
     * @param child the View to scroll to
     */
    private void scrollToChild(View child) {
        child.getDrawingRect(mTempRect);

        /* Offset from child's local coordinates to ScrollView coordinates */
        offsetDescendantRectToMyCoords(child, mTempRect);

        int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);

        if (scrollDelta != 0) {
            scrollBy(0, scrollDelta);
        }
    }

    If rect is off screen, scroll just enough to get it (or at least the
first screen size chunk of it) on screen.
Params: rect –      The rectangle.
immediate – True to scroll immediately without animation
Returns: true if scrolling was performed/**
     * If rect is off screen, scroll just enough to get it (or at least the
     * first screen size chunk of it) on screen.
     *
     * @param rect      The rectangle.
     * @param immediate True to scroll immediately without animation
     * @return true if scrolling was performed
     */
    private boolean scrollToChildRect(Rect rect, boolean immediate) {
        final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
        final boolean scroll = delta != 0;
        if (scroll) {
            if (immediate) {
                scrollBy(0, delta);
            } else {
                smoothScrollBy(0, delta);
            }
        }
        return scroll;
    }

    Compute the amount to scroll in the Y direction in order to get
a rectangle completely on the screen (or, if taller than the screen,
at least the first screen size chunk of it).
Params: rect – The rect.
Returns: The scroll delta./**
     * Compute the amount to scroll in the Y direction in order to get
     * a rectangle completely on the screen (or, if taller than the screen,
     * at least the first screen size chunk of it).
     *
     * @param rect The rect.
     * @return The scroll delta.
     */
    protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect) {
        if (getChildCount() == 0) return 0;

        int height = getHeight();
        int screenTop = getScrollY();
        int screenBottom = screenTop + height;

        int fadingEdge = getVerticalFadingEdgeLength();

        // leave room for top fading edge as long as rect isn't at very top
        if (rect.top > 0) {
            screenTop += fadingEdge;
        }

        // leave room for bottom fading edge as long as rect isn't at very bottom
        if (rect.bottom < getChildAt(0).getHeight()) {
            screenBottom -= fadingEdge;
        }

        int scrollYDelta = 0;

        if (rect.bottom > screenBottom && rect.top > screenTop) {
            // need to move down to get it in view: move down just enough so
            // that the entire rectangle is in view (or at least the first
            // screen size chunk).

            if (rect.height() > height) {
                // just enough to get screen size chunk on
                scrollYDelta += (rect.top - screenTop);
            } else {
                // get entire rect at bottom of screen
                scrollYDelta += (rect.bottom - screenBottom);
            }

            // make sure we aren't scrolling beyond the end of our content
            int bottom = getChildAt(0).getBottom();
            int distanceToBottom = bottom - screenBottom;
            scrollYDelta = Math.min(scrollYDelta, distanceToBottom);

        } else if (rect.top < screenTop && rect.bottom < screenBottom) {
            // need to move up to get it in view: move up just enough so that
            // entire rectangle is in view (or at least the first screen
            // size chunk of it).

            if (rect.height() > height) {
                // screen size chunk
                scrollYDelta -= (screenBottom - rect.bottom);
            } else {
                // entire rect at top
                scrollYDelta -= (screenTop - rect.top);
            }

            // make sure we aren't scrolling any further than the top our content
            scrollYDelta = Math.max(scrollYDelta, -getScrollY());
        }
        return scrollYDelta;
    }

    @Override
    public void requestChildFocus(View child, View focused) {
        if (focused != null && focused.getRevealOnFocusHint()) {
            if (!mIsLayoutDirty) {
                scrollToChild(focused);
            } else {
                // The child may not be laid out yet, we can't compute the scroll yet
                mChildToScrollTo = focused;
            }
        }
        super.requestChildFocus(child, focused);
    }


    When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen. This is more expensive than the default ViewGroup implementation, otherwise this behavior might have been made the default. /**
     * When looking for focus in children of a scroll view, need to be a little
     * more careful not to give focus to something that is scrolled off screen.
     *
     * This is more expensive than the default {@link android.view.ViewGroup}
     * implementation, otherwise this behavior might have been made the default.
     */
    @Override
    protected boolean onRequestFocusInDescendants(int direction,
            Rect previouslyFocusedRect) {

        // convert from forward / backward notation to up / down / left / right
        // (ugh).
        if (direction == View.FOCUS_FORWARD) {
            direction = View.FOCUS_DOWN;
        } else if (direction == View.FOCUS_BACKWARD) {
            direction = View.FOCUS_UP;
        }

        final View nextFocus = previouslyFocusedRect == null ?
                FocusFinder.getInstance().findNextFocus(this, null, direction) :
                FocusFinder.getInstance().findNextFocusFromRect(this,
                        previouslyFocusedRect, direction);

        if (nextFocus == null) {
            return false;
        }

        if (isOffScreen(nextFocus)) {
            return false;
        }

        return nextFocus.requestFocus(direction, previouslyFocusedRect);
    }

    @Override
    public boolean requestChildRectangleOnScreen(View child, Rect rectangle,
            boolean immediate) {
        // offset into coordinate space of this scroll view
        rectangle.offset(child.getLeft() - child.getScrollX(),
                child.getTop() - child.getScrollY());

        return scrollToChildRect(rectangle, immediate);
    }

    @Override
    public void requestLayout() {
        mIsLayoutDirty = true;
        super.requestLayout();
    }

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

        if (mScrollStrictSpan != null) {
            mScrollStrictSpan.finish();
            mScrollStrictSpan = null;
        }
        if (mFlingStrictSpan != null) {
            mFlingStrictSpan.finish();
            mFlingStrictSpan = null;
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        mIsLayoutDirty = false;
        // Give a child focus if it needs it
        if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this)) {
            scrollToChild(mChildToScrollTo);
        }
        mChildToScrollTo = null;

        if (!isLaidOut()) {
            if (mSavedState != null) {
                mScrollY = mSavedState.scrollPosition;
                mSavedState = null;
            } // mScrollY default value is "0"

            final int childHeight = (getChildCount() > 0) ? getChildAt(0).getMeasuredHeight() : 0;
            final int scrollRange = Math.max(0,
                    childHeight - (b - t - mPaddingBottom - mPaddingTop));

            // Don't forget to clamp
            if (mScrollY > scrollRange) {
                mScrollY = scrollRange;
            } else if (mScrollY < 0) {
                mScrollY = 0;
            }
        }

        // Calling this with the present values causes it to re-claim them
        scrollTo(mScrollX, mScrollY);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        View currentFocused = findFocus();
        if (null == currentFocused || this == currentFocused)
            return;

        // If the currently-focused view was visible on the screen when the
        // screen was at the old height, then scroll the screen to make that
        // view visible with the new screen height.
        if (isWithinDeltaOfScreen(currentFocused, 0, oldh)) {
            currentFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(currentFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollY(scrollDelta);
        }
    }

    Return true if child is a descendant of parent, (or equal to the parent).
/**
     * Return true if child is a descendant of parent, (or equal to the parent).
     */
    private static boolean isViewDescendantOf(View child, View parent) {
        if (child == parent) {
            return true;
        }

        final ViewParent theParent = child.getParent();
        return (theParent instanceof ViewGroup) && isViewDescendantOf((View) theParent, parent);
    }

    Fling the scroll view
Params: velocityY – The initial velocity in the Y direction. Positive
                 numbers mean that the finger/cursor is moving down the screen,
                 which means we want to scroll towards the top./**
     * Fling the scroll view
     *
     * @param velocityY The initial velocity in the Y direction. Positive
     *                  numbers mean that the finger/cursor is moving down the screen,
     *                  which means we want to scroll towards the top.
     */
    public void fling(int velocityY) {
        if (getChildCount() > 0) {
            int height = getHeight() - mPaddingBottom - mPaddingTop;
            int bottom = getChildAt(0).getHeight();

            mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0,
                    Math.max(0, bottom - height), 0, height/2);

            if (mFlingStrictSpan == null) {
                mFlingStrictSpan = StrictMode.enterCriticalSpan("ScrollView-fling");
            }

            postInvalidateOnAnimation();
        }
    }

    private void flingWithNestedDispatch(int velocityY) {
        final boolean canFling = (mScrollY > 0 || velocityY > 0) &&
                (mScrollY < getScrollRange() || velocityY < 0);
        if (!dispatchNestedPreFling(0, velocityY)) {
            dispatchNestedFling(0, velocityY, canFling);
            if (canFling) {
                fling(velocityY);
            }
        }
    }

    private void endDrag() {
        mIsBeingDragged = false;

        recycleVelocityTracker();

        if (mEdgeGlowTop != null) {
            mEdgeGlowTop.onRelease();
            mEdgeGlowBottom.onRelease();
        }

        if (mScrollStrictSpan != null) {
            mScrollStrictSpan.finish();
            mScrollStrictSpan = null;
        }
    }

    {@inheritDoc}
This version also clamps the scrolling to the bounds of our child.
/**
     * {@inheritDoc}
     *
     * <p>This version also clamps the scrolling to the bounds of our child.
     */
    @Override
    public void scrollTo(int x, int y) {
        // we rely on the fact the View.scrollBy calls scrollTo.
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
            y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
            if (x != mScrollX || y != mScrollY) {
                super.scrollTo(x, y);
            }
        }
    }

    @Override
    public void setOverScrollMode(int mode) {
        if (mode != OVER_SCROLL_NEVER) {
            if (mEdgeGlowTop == null) {
                Context context = getContext();
                mEdgeGlowTop = new EdgeEffect(context);
                mEdgeGlowBottom = new EdgeEffect(context);
            }
        } else {
            mEdgeGlowTop = null;
            mEdgeGlowBottom = null;
        }
        super.setOverScrollMode(mode);
    }

    @Override
    public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
        return (nestedScrollAxes & SCROLL_AXIS_VERTICAL) != 0;
    }

    @Override
    public void onNestedScrollAccepted(View child, View target, int axes) {
        super.onNestedScrollAccepted(child, target, axes);
        startNestedScroll(SCROLL_AXIS_VERTICAL);
    }

    @inheritDoc /**
     * @inheritDoc
     */
    @Override
    public void onStopNestedScroll(View target) {
        super.onStopNestedScroll(target);
    }

    @Override
    public void onNestedScroll(View target, int dxConsumed, int dyConsumed,
            int dxUnconsumed, int dyUnconsumed) {
        final int oldScrollY = mScrollY;
        scrollBy(0, dyUnconsumed);
        final int myConsumed = mScrollY - oldScrollY;
        final int myUnconsumed = dyUnconsumed - myConsumed;
        dispatchNestedScroll(0, myConsumed, 0, myUnconsumed, null);
    }

    @inheritDoc /**
     * @inheritDoc
     */
    @Override
    public boolean onNestedFling(View target, float velocityX, float velocityY, boolean consumed) {
        if (!consumed) {
            flingWithNestedDispatch((int) velocityY);
            return true;
        }
        return false;
    }

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);
        if (mEdgeGlowTop != null) {
            final int scrollY = mScrollY;
            final boolean clipToPadding = getClipToPadding();
            if (!mEdgeGlowTop.isFinished()) {
                final int restoreCount = canvas.save();
                final int width;
                final int height;
                final float translateX;
                final float translateY;
                if (clipToPadding) {
                    width = getWidth() - mPaddingLeft - mPaddingRight;
                    height = getHeight() - mPaddingTop - mPaddingBottom;
                    translateX = mPaddingLeft;
                    translateY = mPaddingTop;
                } else {
                    width = getWidth();
                    height = getHeight();
                    translateX = 0;
                    translateY = 0;
                }
                canvas.translate(translateX, Math.min(0, scrollY) + translateY);
                mEdgeGlowTop.setSize(width, height);
                if (mEdgeGlowTop.draw(canvas)) {
                    postInvalidateOnAnimation();
                }
                canvas.restoreToCount(restoreCount);
            }
            if (!mEdgeGlowBottom.isFinished()) {
                final int restoreCount = canvas.save();
                final int width;
                final int height;
                final float translateX;
                final float translateY;
                if (clipToPadding) {
                    width = getWidth() - mPaddingLeft - mPaddingRight;
                    height = getHeight() - mPaddingTop - mPaddingBottom;
                    translateX = mPaddingLeft;
                    translateY = mPaddingTop;
                } else {
                    width = getWidth();
                    height = getHeight();
                    translateX = 0;
                    translateY = 0;
                }
                canvas.translate(-width + translateX,
                            Math.max(getScrollRange(), scrollY) + height + translateY);
                canvas.rotate(180, width, 0);
                mEdgeGlowBottom.setSize(width, height);
                if (mEdgeGlowBottom.draw(canvas)) {
                    postInvalidateOnAnimation();
                }
                canvas.restoreToCount(restoreCount);
            }
        }
    }

    private static int clamp(int n, int my, int child) {
        if (my >= child || n < 0) {
            /* my >= child is this case:
             *                    |--------------- me ---------------|
             *     |------ child ------|
             * or
             *     |--------------- me ---------------|
             *            |------ child ------|
             * or
             *     |--------------- me ---------------|
             *                                  |------ child ------|
             *
             * n < 0 is this case:
             *     |------ me ------|
             *                    |-------- child --------|
             *     |-- mScrollX --|
             */
            return 0;
        }
        if ((my+n) > child) {
            /* this case:
             *                    |------ me ------|
             *     |------ child ------|
             *     |-- mScrollX --|
             */
            return child-my;
        }
        return n;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (mContext.getApplicationInfo().targetSdkVersion <= Build.VERSION_CODES.JELLY_BEAN_MR2) {
            // Some old apps reused IDs in ways they shouldn't have.
            // Don't break them, but they don't get scroll state restoration.
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(ss.getSuperState());
        mSavedState = ss;
        requestLayout();
    }

    @Override
    protected Parcelable onSaveInstanceState() {
        if (mContext.getApplicationInfo().targetSdkVersion <= Build.VERSION_CODES.JELLY_BEAN_MR2) {
            // Some old apps reused IDs in ways they shouldn't have.
            // Don't break them, but they don't get scroll state restoration.
            return super.onSaveInstanceState();
        }
        Parcelable superState = super.onSaveInstanceState();
        SavedState ss = new SavedState(superState);
        ss.scrollPosition = mScrollY;
        return ss;
    }

    @hide /** @hide */
    @Override
    protected void encodeProperties(@NonNull ViewHierarchyEncoder encoder) {
        super.encodeProperties(encoder);
        encoder.addProperty("fillViewport", mFillViewport);
    }

    static class SavedState extends BaseSavedState {
        public int scrollPosition;

        SavedState(Parcelable superState) {
            super(superState);
        }

        public SavedState(Parcel source) {
            super(source);
            scrollPosition = source.readInt();
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(scrollPosition);
        }

        @Override
        public String toString() {
            return "ScrollView.SavedState{"
                    + Integer.toHexString(System.identityHashCode(this))
                    + " scrollPosition=" + scrollPosition + "}";
        }

        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

}
Returns:	True if the content fills the viewport, false otherwise.
@attr	ref android.R.styleable#ScrollView_fillViewport
Params:	fillViewport – True to stretch the content's height to the viewport's boundaries, false otherwise.
@attr	ref android.R.styleable#ScrollView_fillViewport
Params:	event – The key event to execute.
Returns:	Return true if the event was handled, else false.
Params:	topFocus – look for a candidate is the one at the top of the bounds if topFocus is true, or at the bottom of the bounds if topFocus is false top – the top offset of the bounds in which a focusable must be found bottom – the bottom offset of the bounds in which a focusable must be found
Returns:	the next focusable component in the bounds or null if none can be found
Params:	direction – the scroll direction: `View.FOCUS_UP` to go one page up or `View.FOCUS_DOWN` to go one page down
Returns:	true if the key event is consumed by this method, false otherwise
Params:	direction – The direction corresponding to the arrow key that was pressed
Returns:	True if we consumed the event, false otherwise
Params:	rect – The rectangle. immediate – True to scroll immediately without animation
Returns:	true if scrolling was performed
/

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