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Commit 10ba2773 authored by Adam Powell's avatar Adam Powell
Browse files

Nested scrolling! 

or, "Excuse me, Egon, you said crossing the streams was bad."

Add API for driving a nested scroll from the most deeply nested
applicable scrolling view. The deepest scrolling view dispatches
high-level scrolling events up to cooperative parent views.

Augment ScrollView to support nested scrolling. Next up, more public
framework scrolling views.

Change-Id: I53b5e207fcdece796e08c8592ddb4496b96f600e
parent 80021878

api/current.txt

+31 −6
Original line number Diff line number Diff line
@@ -825,6 +825,7 @@ package android { 
    field public static final int name = 16842755; // 0x1010003

    field public static final int navigationMode = 16843471; // 0x10102cf

    field public static final int negativeButtonText = 16843254; // 0x10101f6

    field public static final int nestedScrollingEnabled = 16843843; // 0x1010443

    field public static final int nextFocusDown = 16842980; // 0x10100e4

    field public static final int nextFocusForward = 16843580; // 0x101033c

    field public static final int nextFocusLeft = 16842977; // 0x10100e1
@@ -1285,8 +1286,8 @@ package android { 
    field public static final int windowActionBar = 16843469; // 0x10102cd

    field public static final int windowActionBarOverlay = 16843492; // 0x10102e4

    field public static final int windowActionModeOverlay = 16843485; // 0x10102dd

    field public static final int windowAllowEnterTransitionOverlap = 16843848; // 0x1010448

    field public static final int windowAllowExitTransitionOverlap = 16843847; // 0x1010447

    field public static final int windowAllowEnterTransitionOverlap = 16843849; // 0x1010449

    field public static final int windowAllowExitTransitionOverlap = 16843848; // 0x1010448

    field public static final int windowAnimationStyle = 16842926; // 0x10100ae

    field public static final int windowBackground = 16842836; // 0x1010054

    field public static final int windowCloseOnTouchOutside = 16843611; // 0x101035b
@@ -1296,9 +1297,9 @@ package android { 
    field public static final int windowDisablePreview = 16843298; // 0x1010222

    field public static final int windowEnableSplitTouch = 16843543; // 0x1010317

    field public static final int windowEnterAnimation = 16842932; // 0x10100b4

    field public static final int windowEnterTransition = 16843843; // 0x1010443

    field public static final int windowEnterTransition = 16843844; // 0x1010444

    field public static final int windowExitAnimation = 16842933; // 0x10100b5

    field public static final int windowExitTransition = 16843844; // 0x1010444

    field public static final int windowExitTransition = 16843845; // 0x1010445

    field public static final int windowFrame = 16842837; // 0x1010055

    field public static final int windowFullscreen = 16843277; // 0x101020d

    field public static final int windowHideAnimation = 16842935; // 0x10100b7
@@ -1309,8 +1310,8 @@ package android { 
    field public static final int windowNoDisplay = 16843294; // 0x101021e

    field public static final int windowNoTitle = 16842838; // 0x1010056

    field public static final int windowOverscan = 16843727; // 0x10103cf

    field public static final int windowSharedElementEnterTransition = 16843845; // 0x1010445

    field public static final int windowSharedElementExitTransition = 16843846; // 0x1010446

    field public static final int windowSharedElementEnterTransition = 16843846; // 0x1010446

    field public static final int windowSharedElementExitTransition = 16843847; // 0x1010447

    field public static final int windowShowAnimation = 16842934; // 0x10100b6

    field public static final int windowShowWallpaper = 16843410; // 0x1010292

    field public static final int windowSoftInputMode = 16843307; // 0x101022b
@@ -29983,6 +29984,9 @@ package android.view { 
    method public boolean dispatchKeyEvent(android.view.KeyEvent);

    method public boolean dispatchKeyEventPreIme(android.view.KeyEvent);

    method public boolean dispatchKeyShortcutEvent(android.view.KeyEvent);

    method public boolean dispatchNestedFling(float, float);

    method public boolean dispatchNestedPreScroll(int, int, int[], int[]);

    method public boolean dispatchNestedScroll(int, int, int, int, int[]);

    method public boolean dispatchPopulateAccessibilityEvent(android.view.accessibility.AccessibilityEvent);

    method protected void dispatchRestoreInstanceState(android.util.SparseArray<android.os.Parcelable>);

    method protected void dispatchSaveInstanceState(android.util.SparseArray<android.os.Parcelable>);
@@ -30132,6 +30136,7 @@ package android.view { 
    method public float getY();

    method public boolean hasFocus();

    method public boolean hasFocusable();

    method public boolean hasNestedScrollingParent();

    method public boolean hasOnClickListeners();

    method public boolean hasOverlappingRendering();

    method public boolean hasTransientState();
@@ -30167,6 +30172,7 @@ package android.view { 
    method public boolean isLayoutDirectionResolved();

    method public boolean isLayoutRequested();

    method public boolean isLongClickable();

    method public boolean isNestedScrollingEnabled();

    method public boolean isOpaque();

    method protected boolean isPaddingOffsetRequired();

    method public boolean isPaddingRelative();
@@ -30318,6 +30324,7 @@ package android.view { 
    method protected final void setMeasuredDimension(int, int);

    method public void setMinimumHeight(int);

    method public void setMinimumWidth(int);

    method public void setNestedScrollingEnabled(boolean);

    method public void setNextFocusDownId(int);

    method public void setNextFocusForwardId(int);

    method public void setNextFocusLeftId(int);
@@ -30382,6 +30389,8 @@ package android.view { 
    method public android.view.ActionMode startActionMode(android.view.ActionMode.Callback);

    method public void startAnimation(android.view.animation.Animation);

    method public final boolean startDrag(android.content.ClipData, android.view.View.DragShadowBuilder, java.lang.Object, int);

    method public boolean startNestedScroll(int);

    method public void stopNestedScroll();

    method public void unscheduleDrawable(android.graphics.drawable.Drawable, java.lang.Runnable);

    method public void unscheduleDrawable(android.graphics.drawable.Drawable);

    method protected boolean verifyDrawable(android.graphics.drawable.Drawable);
@@ -30470,6 +30479,9 @@ package android.view { 
    field public static final int SCROLLBAR_POSITION_DEFAULT = 0; // 0x0

    field public static final int SCROLLBAR_POSITION_LEFT = 1; // 0x1

    field public static final int SCROLLBAR_POSITION_RIGHT = 2; // 0x2

    field public static final int SCROLL_AXIS_HORIZONTAL = 1; // 0x1

    field public static final int SCROLL_AXIS_NONE = 0; // 0x0

    field public static final int SCROLL_AXIS_VERTICAL = 2; // 0x2

    field protected static final int[] SELECTED_STATE_SET;

    field protected static final int[] SELECTED_WINDOW_FOCUSED_STATE_SET;

    field public static final int SOUND_EFFECTS_ENABLED = 134217728; // 0x8000000
@@ -30739,6 +30751,7 @@ package android.view { 
    method public android.view.animation.Animation.AnimationListener getLayoutAnimationListener();

    method public int getLayoutMode();

    method public android.animation.LayoutTransition getLayoutTransition();

    method public int getNestedScrollAxes();

    method public int getPersistentDrawingCache();

    method public int indexOfChild(android.view.View);

    method public final void invalidateChild(android.view.View, android.graphics.Rect);
@@ -30759,8 +30772,14 @@ package android.view { 
    method public boolean onInterceptHoverEvent(android.view.MotionEvent);

    method public boolean onInterceptTouchEvent(android.view.MotionEvent);

    method protected abstract void onLayout(boolean, int, int, int, int);

    method public boolean onNestedFling(android.view.View, float, float);

    method public void onNestedPreScroll(android.view.View, int, int, int[]);

    method public void onNestedScroll(android.view.View, int, int, int, int);

    method public void onNestedScrollAccepted(android.view.View, android.view.View, int);

    method protected boolean onRequestFocusInDescendants(int, android.graphics.Rect);

    method public boolean onRequestSendAccessibilityEvent(android.view.View, android.view.accessibility.AccessibilityEvent);

    method public boolean onStartNestedScroll(android.view.View, android.view.View, int);

    method public void onStopNestedScroll(android.view.View);

    method public void recomputeViewAttributes(android.view.View);

    method public void removeAllViews();

    method public void removeAllViewsInLayout();
@@ -30891,6 +30910,12 @@ package android.view { 
    method public abstract boolean isTextAlignmentResolved();

    method public abstract boolean isTextDirectionResolved();

    method public abstract void notifySubtreeAccessibilityStateChanged(android.view.View, android.view.View, int);

    method public abstract boolean onNestedFling(android.view.View, float, float);

    method public abstract void onNestedPreScroll(android.view.View, int, int, int[]);

    method public abstract void onNestedScroll(android.view.View, int, int, int, int);

    method public abstract void onNestedScrollAccepted(android.view.View, android.view.View, int);

    method public abstract boolean onStartNestedScroll(android.view.View, android.view.View, int);

    method public abstract void onStopNestedScroll(android.view.View);

    method public abstract void recomputeViewAttributes(android.view.View);

    method public abstract void requestChildFocus(android.view.View, android.view.View);

    method public abstract boolean requestChildRectangleOnScreen(android.view.View, android.graphics.Rect, boolean);

core/java/android/view/View.java

+300 −7
Original line number Diff line number Diff line
@@ -27,7 +27,6 @@ import android.content.res.Configuration; 
import android.content.res.Resources;

import android.content.res.TypedArray;

import android.graphics.Bitmap;

import android.graphics.Camera;

import android.graphics.Canvas;

import android.graphics.Insets;

import android.graphics.Interpolator;
@@ -2395,6 +2394,13 @@ public class View implements Drawable.Callback, KeyEvent.Callback, 
     */

    static final int PFLAG3_FITTING_SYSTEM_WINDOWS = 0x100;













    /**













     * Flag indicating that nested scrolling is enabled for this view.













     * The view will optionally cooperate with views up its parent chain to allow for













     * integrated nested scrolling along the same axis.













     */













    static final int PFLAG3_NESTED_SCROLLING_ENABLED = 0x200;



























    /* End of masks for mPrivateFlags3 */





























    static final int DRAG_MASK = PFLAG2_DRAG_CAN_ACCEPT | PFLAG2_DRAG_HOVERED;










@@ -2846,6 +2852,21 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













     */















    public static final int SCREEN_STATE_ON = 0x1;



























    /**













     * Indicates no axis of view scrolling.













     */













    public static final int SCROLL_AXIS_NONE = 0;

























    /**













     * Indicates scrolling along the horizontal axis.













     */













    public static final int SCROLL_AXIS_HORIZONTAL = 1 << 0;

























    /**













     * Indicates scrolling along the vertical axis.













     */













    public static final int SCROLL_AXIS_VERTICAL = 1 << 1;



























    /**















     * Controls the over-scroll mode for this view.















     * See {@link #overScrollBy(int, int, int, int, int, int, int, int, boolean)},










@@ -3472,6 +3493,14 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













     */















    ViewOverlay mOverlay;



























    /**













     * The currently active parent view for receiving delegated nested scrolling events.













     * This is set by {@link #startNestedScroll(int)} during a touch interaction and cleared













     * by {@link #stopNestedScroll()} at the same point where we clear













     * requestDisallowInterceptTouchEvent.













     */













    private ViewParent mNestedScrollingParent;



























    /**















     * Consistency verifier for debugging purposes.















     * @hide









@@ -3482,6 +3511,8 @@ public class View implements Drawable.Callback, KeyEvent.Callback,



























    private static final AtomicInteger sNextGeneratedId = new AtomicInteger(1);



























    private int[] mTempNestedScrollConsumed;



























    /**















     * Simple constructor to use when creating a view from code.















     *










@@ -3963,6 +3994,9 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













                case R.styleable.View_sharedElementName:















                    setSharedElementName(a.getString(attr));















                    break;













                case R.styleable.View_nestedScrollingEnabled:













                    setNestedScrollingEnabled(a.getBoolean(attr, false));













                    break;















            }















        }
























@@ -7976,27 +8010,46 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













     * @return True if the event was handled by the view, false otherwise.















     */















    public boolean dispatchTouchEvent(MotionEvent event) {













        boolean result = false;



























        if (mInputEventConsistencyVerifier != null) {















            mInputEventConsistencyVerifier.onTouchEvent(event, 0);















        }



























        final int actionMasked = event.getActionMasked();













        if (actionMasked == MotionEvent.ACTION_DOWN) {













            // Defensive cleanup for new gesture













            stopNestedScroll();













        }



























        if (onFilterTouchEventForSecurity(event)) {















            //noinspection SimplifiableIfStatement















            ListenerInfo li = mListenerInfo;













            if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED













            if (li != null && li.mOnTouchListener != null













                    && (mViewFlags & ENABLED_MASK) == ENABLED















                    && li.mOnTouchListener.onTouch(this, event)) {













                return true;













                result = true;















            }



























            if (onTouchEvent(event)) {













                return true;













            if (!result && onTouchEvent(event)) {













                result = true;















            }















        }



























        if (mInputEventConsistencyVerifier != null) {













        if (!result && mInputEventConsistencyVerifier != null) {















            mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);















        }













        return false;

























        // Clean up after nested scrolls if this is the end of a gesture;













        // also cancel it if we tried an ACTION_DOWN but we didn't want the rest













        // of the gesture.













        if (actionMasked == MotionEvent.ACTION_UP ||













                actionMasked == MotionEvent.ACTION_CANCEL ||













                (actionMasked == MotionEvent.ACTION_DOWN && !result)) {













            stopNestedScroll();













        }

























        return result;















    }





























    /**










@@ -12735,6 +12788,7 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













        removeLongPressCallback();















        removePerformClickCallback();















        removeSendViewScrolledAccessibilityEventCallback();













        stopNestedScroll();





























        destroyDrawingCache();















        destroyLayer(false);










@@ -17900,6 +17954,245 @@ public class View implements Drawable.Callback, KeyEvent.Callback,













        mOverScrollMode = overScrollMode;















    }



























    /**













     * Enable or disable nested scrolling for this view.













     *













     * <p>If this property is set to true the view will be permitted to initiate nested













     * scrolling operations with a compatible parent view in the current hierarchy. If this













     * view does not implement nested scrolling this will have no effect.</p>













     *













     * @param enabled true to enable nested scrolling, false to disable













     *













     * @see #isNestedScrollingEnabled()













     */













    public void setNestedScrollingEnabled(boolean enabled) {













        if (enabled) {













            mPrivateFlags3 |= PFLAG3_NESTED_SCROLLING_ENABLED;













        } else {













            mPrivateFlags3 &= ~PFLAG3_NESTED_SCROLLING_ENABLED;













        }













    }

























    /**













     * Returns true if nested scrolling is enabled for this view.













     *













     * <p>If nested scrolling is enabled and this View class implementation supports it,













     * this view will act as a nested scrolling child view when applicable, forwarding data













     * about the scroll operation in progress to a compatible and cooperating nested scrolling













     * parent.</p>













     *













     * @return true if nested scrolling is enabled













     *













     * @see #setNestedScrollingEnabled(boolean)













     */













    public boolean isNestedScrollingEnabled() {













        return (mPrivateFlags3 & PFLAG3_NESTED_SCROLLING_ENABLED) ==













                PFLAG3_NESTED_SCROLLING_ENABLED;













    }

























    /**













     * Begin a nestable scroll operation along the given axes.













     *













     * <p>A view starting a nested scroll promises to abide by the following contract:</p>













     *













     * <p>The view will call startNestedScroll upon initiating a scroll operation. In the case













     * of a touch scroll this corresponds to the initial {@link MotionEvent#ACTION_DOWN}.













     * In the case of touch scrolling the nested scroll will be terminated automatically in













     * the same manner as {@link ViewParent#requestDisallowInterceptTouchEvent(boolean)}.













     * In the event of programmatic scrolling the caller must explicitly call













     * {@link #stopNestedScroll()} to indicate the end of the nested scroll.</p>













     *













     * <p>If <code>startNestedScroll</code> returns true, a cooperative parent was found.













     * If it returns false the caller may ignore the rest of this contract until the next scroll.













     * </p>













     *













     * <p>At each incremental step of the scroll the caller should invoke













     * {@link #dispatchNestedPreScroll(int, int, int[], int[]) dispatchNestedPreScroll}













     * once it has calculated the requested scrolling delta. If it returns true the nested scrolling













     * parent at least partially consumed the scroll and the caller should adjust the amount it













     * scrolls by.</p>













     *













     * <p>After applying the remainder of the scroll delta the caller should invoke













     * {@link #dispatchNestedScroll(int, int, int, int, int[]) dispatchNestedScroll}, passing













     * both the delta consumed and the delta unconsumed. A nested scrolling parent may treat













     * these values differently. See {@link ViewParent#onNestedScroll(View, int, int, int, int)}.













     * </p>













     *













     * @param axes Flags consisting of a combination of {@link #SCROLL_AXIS_HORIZONTAL} and/or













     *             {@link #SCROLL_AXIS_VERTICAL}.













     * @return true if a cooperative parent was found and nested scrolling has been enabled for













     *         the current gesture.













     *













     * @see #stopNestedScroll()













     * @see #dispatchNestedPreScroll(int, int, int[], int[])













     * @see #dispatchNestedScroll(int, int, int, int, int[])













     */













    public boolean startNestedScroll(int axes) {













        if (isNestedScrollingEnabled()) {













            ViewParent p = getParent();













            View child = this;













            while (p != null) {













                try {













                    if (p.onStartNestedScroll(child, this, axes)) {













                        mNestedScrollingParent = p;













                        p.onNestedScrollAccepted(child, this, axes);













                        return true;













                    }













                } catch (AbstractMethodError e) {













                    Log.e(VIEW_LOG_TAG, "ViewParent " + p + " does not implement interface " +













                            "method onStartNestedScroll", e);













                    // Allow the search upward to continue













                }













                if (p instanceof View) {













                    child = (View) p;













                }













                p = p.getParent();













            }













        }













        return false;













    }

























    /**













     * Stop a nested scroll in progress.













     *













     * <p>Calling this method when a nested scroll is not currently in progress is harmless.</p>













     *













     * @see #startNestedScroll(int)













     */













    public void stopNestedScroll() {













        if (mNestedScrollingParent != null) {













            mNestedScrollingParent.onStopNestedScroll(this);













            mNestedScrollingParent = null;













        }













    }

























    /**













     * Returns true if this view has a nested scrolling parent.













     *













     * <p>The presence of a nested scrolling parent indicates that this view has initiated













     * a nested scroll and it was accepted by an ancestor view further up the view hierarchy.</p>













     *













     * @return whether this view has a nested scrolling parent













     */













    public boolean hasNestedScrollingParent() {













        return mNestedScrollingParent != null;













    }

























    /**













     * Dispatch one step of a nested scroll in progress.













     *













     * <p>Implementations of views that support nested scrolling should call this to report













     * info about a scroll in progress to the current nested scrolling parent. If a nested scroll













     * is not currently in progress or nested scrolling is not













     * {@link #isNestedScrollingEnabled() enabled} for this view this method does nothing.</p>













     *













     * <p>Compatible View implementations should also call













     * {@link #dispatchNestedPreScroll(int, int, int[], int[]) dispatchNestedPreScroll} before













     * consuming a component of the scroll event themselves.</p>













     *













     * @param dxConsumed Horizontal distance in pixels consumed by this view during this scroll step













     * @param dyConsumed Vertical distance in pixels consumed by this view during this scroll step













     * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by this view













     * @param dyUnconsumed Horizontal scroll distance in pixels not consumed by this view













     * @param offsetInWindow Optional. If not null, on return this will contain the offset













     *                       in local view coordinates of this view from before this operation













     *                       to after it completes. View implementations may use this to adjust













     *                       expected input coordinate tracking.













     * @return true if the event was dispatched, false if it could not be dispatched.













     * @see #dispatchNestedPreScroll(int, int, int[], int[])













     */













    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,













            int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {













        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {













            int startX = 0;













            int startY = 0;













            if (offsetInWindow != null) {













                getLocationInWindow(offsetInWindow);













                startX = offsetInWindow[0];













                startY = offsetInWindow[1];













            }

























            mNestedScrollingParent.onNestedScroll(this, dxConsumed, dyConsumed,













                    dxUnconsumed, dyUnconsumed);

























            if (offsetInWindow != null) {













                getLocationInWindow(offsetInWindow);













                offsetInWindow[0] -= startX;













                offsetInWindow[1] -= startY;













            }













            return true;













        }













        return false;













    }

























    /**













     * Dispatch one step of a nested scroll in progress before this view consumes any portion of it.













     *













     * <p>Nested pre-scroll events are to nested scroll events what touch intercept is to touch.













     * <code>dispatchNestedPreScroll</code> offers an opportunity for the parent view in a nested













     * scrolling operation to consume some or all of the scroll operation before the child view













     * consumes it.</p>













     *













     * @param dx Horizontal scroll distance in pixels













     * @param dy Vertical scroll distance in pixels













     * @param consumed Output. If not null, consumed[0] will contain the consumed component of dx













     *                 and consumed[1] the consumed dy.













     * @param offsetInWindow Optional. If not null, on return this will contain the offset













     *                       in local view coordinates of this view from before this operation













     *                       to after it completes. View implementations may use this to adjust













     *                       expected input coordinate tracking.













     * @return true if the parent consumed some or all of the scroll delta













     * @see #dispatchNestedScroll(int, int, int, int, int[])













     */













    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {













        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {













            int startX = 0;













            int startY = 0;













            if (offsetInWindow != null) {













                getLocationInWindow(offsetInWindow);













                startX = offsetInWindow[0];













                startY = offsetInWindow[1];













            }

























            if (consumed == null) {













                if (mTempNestedScrollConsumed == null) {













                    mTempNestedScrollConsumed = new int[2];













                }













                consumed = mTempNestedScrollConsumed;













            }













            consumed[0] = 0;













            consumed[1] = 0;













            mNestedScrollingParent.onNestedPreScroll(this, dx, dy, consumed);

























            if (offsetInWindow != null) {













                getLocationInWindow(offsetInWindow);













                offsetInWindow[0] -= startX;













                offsetInWindow[1] -= startY;













            }













            return consumed[0] != 0 || consumed[1] != 0;













        }













        return false;













    }

























    /**













     * Dispatch a fling to a nested scrolling parent.













     *













     * <p>If a nested scrolling child view would normally fling but it is at the edge of its













     * own content it should use this method to delegate the fling to its nested scrolling parent.













     * The view implementation can use a {@link VelocityTracker} to obtain the velocity values













     * to pass.</p>













     *













     * @param velocityX Horizontal fling velocity in pixels per second













     * @param velocityY Vertical fling velocity in pixels per second













     * @return true if the nested scrolling parent consumed the fling













     */













    public boolean dispatchNestedFling(float velocityX, float velocityY) {













        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {













            return mNestedScrollingParent.onNestedFling(this, velocityX, velocityY);













        }













        return false;













    }



























    /**















     * Gets a scale factor that determines the distance the view should scroll















     * vertically in response to {@link MotionEvent#ACTION_SCROLL}.

























core/java/android/view/ViewGroup.java



+76
−0


























File changed.
Preview size limit exceeded, changes collapsed.
























core/java/android/view/ViewParent.java



+115
−0


























File changed.
Preview size limit exceeded, changes collapsed.
























core/java/android/view/ViewRootImpl.java



+27
−0




























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@@ -6090,6 +6090,33 @@ public final class ViewRootImpl implements ViewParent,













        // Do nothing.















    }





























    @Override













    public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {













        return false;













    }



























    @Override













    public void onStopNestedScroll(View target) {













    }



























    @Override













    public void onNestedScrollAccepted(View child, View target, int nestedScrollAxes) {













    }



























    @Override













    public void onNestedScroll(View target, int dxConsumed, int dyConsumed,













            int dxUnconsumed, int dyUnconsumed) {













    }



























    @Override













    public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) {













    }



























    @Override













    public boolean onNestedFling(View target, float velocityX, float velocityY) {













        return false;













    }





























    void changeCanvasOpacity(boolean opaque) {















        // TODO(romainguy): recreate Canvas (software or hardware) to reflect the opacity change.















        Log.d(TAG, "changeCanvasOpacity: opaque=" + opaque);