Android学习分享：执行某ViewGroup的动画时，子控件太多导致动画执行卡顿的问题

    /**
     * Enables or disables the children‘s drawing cache during a layout animation.
     * By default, the drawing cache is enabled but this will prevent nested
     * layout animations from working. To nest animations, you must disable the
     * cache.
     *
     * @param enabled true to enable the animation cache, false otherwise
     *
     * @see #isAnimationCacheEnabled()
     * @see View#setDrawingCacheEnabled(boolean)
     */
    public void setAnimationCacheEnabled(boolean enabled) {
        setBooleanFlag(FLAG_ANIMATION_CACHE, enabled);
    }

    /**
     * <p>Forces the drawing cache to be built if the drawing cache is invalid.</p>
     *
     * <p>If you call {@link #buildDrawingCache()} manually without calling
     * {@link #setDrawingCacheEnabled(boolean) setDrawingCacheEnabled(true)}, you
     * should cleanup the cache by calling {@link #destroyDrawingCache()} afterwards.</p>
     *
     * <p>Note about auto scaling in compatibility mode: When auto scaling is not enabled,
     * this method will create a bitmap of the same size as this view. Because this bitmap
     * will be drawn scaled by the parent ViewGroup, the result on screen might show
     * scaling artifacts. To avoid such artifacts, you should call this method by setting
     * the auto scaling to true. Doing so, however, will generate a bitmap of a different
     * size than the view. This implies that your application must be able to handle this
     * size.</p>
     *
     * <p>You should avoid calling this method when hardware acceleration is enabled. If
     * you do not need the drawing cache bitmap, calling this method will increase memory
     * usage and cause the view to be rendered in software once, thus negatively impacting
     * performance.</p>
     *
     * @see #getDrawingCache()
     * @see #destroyDrawingCache()
     */
    public void buildDrawingCache(boolean autoScale) {
        if ((mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == 0 || (autoScale ?
                mDrawingCache == null : mUnscaledDrawingCache == null)) {
            mCachingFailed = false;

            int width = mRight - mLeft;
            int height = mBottom - mTop;

            final AttachInfo attachInfo = mAttachInfo;
            final boolean scalingRequired = attachInfo != null && attachInfo.mScalingRequired;

            if (autoScale && scalingRequired) {
                width = (int) ((width * attachInfo.mApplicationScale) + 0.5f);
                height = (int) ((height * attachInfo.mApplicationScale) + 0.5f);
            }

            final int drawingCacheBackgroundColor = mDrawingCacheBackgroundColor;
　　　　　　　// 1.这里
            final boolean opaque = drawingCacheBackgroundColor != 0 || isOpaque();
            final boolean use32BitCache = attachInfo != null && attachInfo.mUse32BitDrawingCache;

            final long projectedBitmapSize = width * height * (opaque && !use32BitCache ? 2 : 4);
            final long drawingCacheSize =
                    ViewConfiguration.get(mContext).getScaledMaximumDrawingCacheSize();
            if (width <= 0 || height <= 0 || projectedBitmapSize > drawingCacheSize) {
                if (width > 0 && height > 0) {
                    Log.w(VIEW_LOG_TAG, "View too large to fit into drawing cache, needs "
                            + projectedBitmapSize + " bytes, only "
                            + drawingCacheSize + " available");
                }
                destroyDrawingCache();
                mCachingFailed = true;
                return;
            }

            boolean clear = true;
            Bitmap bitmap = autoScale ? mDrawingCache : mUnscaledDrawingCache;

            if (bitmap == null || bitmap.getWidth() != width || bitmap.getHeight() != height) {
                Bitmap.Config quality;
　　　　　　　　　 // 2.这里
                if (!opaque) {
                    // Never pick ARGB_4444 because it looks awful
                    // Keep the DRAWING_CACHE_QUALITY_LOW flag just in case
                    switch (mViewFlags & DRAWING_CACHE_QUALITY_MASK) {
                        case DRAWING_CACHE_QUALITY_AUTO:
                        case DRAWING_CACHE_QUALITY_LOW:
                        case DRAWING_CACHE_QUALITY_HIGH:
                        default:
                            quality = Bitmap.Config.ARGB_8888;
                            break;
                    }
                } else {
                    // Optimization for translucent windows
                    // If the window is translucent, use a 32 bits bitmap to benefit from memcpy()
                    quality = use32BitCache ? Bitmap.Config.ARGB_8888 : Bitmap.Config.RGB_565;
                }

                // Try to cleanup memory
                if (bitmap != null) bitmap.recycle();

                try {
                    bitmap = Bitmap.createBitmap(mResources.getDisplayMetrics(),
                            width, height, quality);
                    bitmap.setDensity(getResources().getDisplayMetrics().densityDpi);
                    if (autoScale) {
                        mDrawingCache = bitmap;
                    } else {
                        mUnscaledDrawingCache = bitmap;
                    }
                    if (opaque && use32BitCache) bitmap.setHasAlpha(false);
                } catch (OutOfMemoryError e) {
                    // If there is not enough memory to create the bitmap cache, just
                    // ignore the issue as bitmap caches are not required to draw the
                    // view hierarchy
                    if (autoScale) {
                        mDrawingCache = null;
                    } else {
                        mUnscaledDrawingCache = null;
                    }
                    mCachingFailed = true;
                    return;
                }

                clear = drawingCacheBackgroundColor != 0;
            }

            Canvas canvas;
            if (attachInfo != null) {
                canvas = attachInfo.mCanvas;
                if (canvas == null) {
                    canvas = new Canvas();
                }
                canvas.setBitmap(bitmap);
                // Temporarily clobber the cached Canvas in case one of our children
                // is also using a drawing cache. Without this, the children would
                // steal the canvas by attaching their own bitmap to it and bad, bad
                // thing would happen (invisible views, corrupted drawings, etc.)
                attachInfo.mCanvas = null;
            } else {
                // This case should hopefully never or seldom happen
                canvas = new Canvas(bitmap);
            }

            if (clear) {
                bitmap.eraseColor(drawingCacheBackgroundColor);
            }

            computeScroll();
            final int restoreCount = canvas.save();

            if (autoScale && scalingRequired) {
                final float scale = attachInfo.mApplicationScale;
                canvas.scale(scale, scale);
            }

            canvas.translate(-mScrollX, -mScrollY);

            mPrivateFlags |= PFLAG_DRAWN;
            if (mAttachInfo == null || !mAttachInfo.mHardwareAccelerated ||
                    mLayerType != LAYER_TYPE_NONE) {
                mPrivateFlags |= PFLAG_DRAWING_CACHE_VALID;
            }

            // Fast path for layouts with no backgrounds
            if ((mPrivateFlags & PFLAG_SKIP_DRAW) == PFLAG_SKIP_DRAW) {
                mPrivateFlags &= ~PFLAG_DIRTY_MASK;
                dispatchDraw(canvas);
                if (mOverlay != null && !mOverlay.isEmpty()) {
                    mOverlay.getOverlayView().draw(canvas);
                }
            } else {
                draw(canvas);
            }

            canvas.restoreToCount(restoreCount);
            canvas.setBitmap(null);

            if (attachInfo != null) {
                // Restore the cached Canvas for our siblings
                attachInfo.mCanvas = canvas;
            }
        }
    }

setDrawingCacheBackgroundColor(0xFF0C0C0C);

    /**
     * {@inheritDoc}
     */
    @Override
    protected void dispatchDraw(Canvas canvas) {
        final int count = mChildrenCount;
        final View[] children = mChildren;
        int flags = mGroupFlags;
　　　　　// 关键字：FLAG_RUN_ANIMATION，FLAG_ANIMATION_CACHE，cache，buildCache
        if ((flags & FLAG_RUN_ANIMATION) != 0 && canAnimate()) {
            final boolean cache = (mGroupFlags & FLAG_ANIMATION_CACHE) == FLAG_ANIMATION_CACHE;

            final boolean buildCache = !isHardwareAccelerated();
            for (int i = 0; i < count; i++) {
                final View child = children[i];
                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
                    final LayoutParams params = child.getLayoutParams();
                    attachLayoutAnimationParameters(child, params, i, count);
                    bindLayoutAnimation(child);
                    if (cache) {
                        child.setDrawingCacheEnabled(true);
                        if (buildCache) {                        
                            child.buildDrawingCache(true);
                        }
                    }
                }
            }

            final LayoutAnimationController controller = mLayoutAnimationController;
            if (controller.willOverlap()) {
                mGroupFlags |= FLAG_OPTIMIZE_INVALIDATE;
            }

            controller.start();

            mGroupFlags &= ~FLAG_RUN_ANIMATION;
            mGroupFlags &= ~FLAG_ANIMATION_DONE;

            if (cache) {
                mGroupFlags |= FLAG_CHILDREN_DRAWN_WITH_CACHE;
            }

            if (mAnimationListener != null) {
                mAnimationListener.onAnimationStart(controller.getAnimation());
            }
        }

        int saveCount = 0;
        final boolean clipToPadding = (flags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK;
        if (clipToPadding) {
            saveCount = canvas.save();
            canvas.clipRect(mScrollX + mPaddingLeft, mScrollY + mPaddingTop,
                    mScrollX + mRight - mLeft - mPaddingRight,
                    mScrollY + mBottom - mTop - mPaddingBottom);

        }

        // We will draw our child‘s animation, let‘s reset the flag
        mPrivateFlags &= ~PFLAG_DRAW_ANIMATION;
        mGroupFlags &= ~FLAG_INVALIDATE_REQUIRED;

        boolean more = false;
        final long drawingTime = getDrawingTime();

        if ((flags & FLAG_USE_CHILD_DRAWING_ORDER) == 0) {
            for (int i = 0; i < count; i++) {
                final View child = children[i];
                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {
                    more |= drawChild(canvas, child, drawingTime);
                }
            }
        } else {
            for (int i = 0; i < count; i++) {
                final View child = children[getChildDrawingOrder(count, i)];
                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {
                    more |= drawChild(canvas, child, drawingTime);
                }
            }
        }

        // Draw any disappearing views that have animations
        if (mDisappearingChildren != null) {
            final ArrayList<View> disappearingChildren = mDisappearingChildren;
            final int disappearingCount = disappearingChildren.size() - 1;
            // Go backwards -- we may delete as animations finish
            for (int i = disappearingCount; i >= 0; i--) {
                final View child = disappearingChildren.get(i);
                more |= drawChild(canvas, child, drawingTime);
            }
        }

        if (debugDraw()) {
            onDebugDraw(canvas);
        }

        if (clipToPadding) {
            canvas.restoreToCount(saveCount);
        }

        // mGroupFlags might have been updated by drawChild()
        flags = mGroupFlags;

        if ((flags & FLAG_INVALIDATE_REQUIRED) == FLAG_INVALIDATE_REQUIRED) {
            invalidate(true);
        }

        if ((flags & FLAG_ANIMATION_DONE) == 0 && (flags & FLAG_NOTIFY_ANIMATION_LISTENER) == 0 &&
                mLayoutAnimationController.isDone() && !more) {
            // We want to erase the drawing cache and notify the listener after the
            // next frame is drawn because one extra invalidate() is caused by
            // drawChild() after the animation is over
            mGroupFlags |= FLAG_NOTIFY_ANIMATION_LISTENER;
            final Runnable end = new Runnable() {
               public void run() {
                   notifyAnimationListener();
               }
            };
            post(end);
        }
    }

boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) {
    boolean caching;
    ……………
    final int flags = parent.mGroupFlags;
    …………..
    if ((flags & ViewGroup.FLAG_CHILDREN_DRAWN_WITH_CACHE) != 0 ||
                (flags & ViewGroup.FLAG_ALWAYS_DRAWN_WITH_CACHE) != 0) {
            caching = true;
            // Auto-scaled apps are not hw-accelerated, no need to set scaling flag on DisplayList
            if (mAttachInfo != null) scalingRequired =         mAttachInfo.mScalingRequired;
        } else {
            caching = (layerType != LAYER_TYPE_NONE) || hardwareAccelerated;
        }
    …………..
    if (caching) {
            if (!hardwareAccelerated) {
                if (layerType != LAYER_TYPE_NONE) {
                    layerType = LAYER_TYPE_SOFTWARE;
                    buildDrawingCache(true);
                }
                cache = getDrawingCache(true);
            } else {
                switch (layerType) {
                    case LAYER_TYPE_SOFTWARE:
                        if (useDisplayListProperties) {
                            hasDisplayList = canHaveDisplayList();
                        } else {
                            buildDrawingCache(true);
                            cache = getDrawingCache(true);
                        }
                        break;
                    case LAYER_TYPE_HARDWARE:
                        if (useDisplayListProperties) {
                            hasDisplayList = canHaveDisplayList();
                        }
                        break;
                    case LAYER_TYPE_NONE:
                        // Delay getting the display list until animation-driven alpha values are
                        // set up and possibly passed on to the view
                        hasDisplayList = canHaveDisplayList();
                        break;
                }
            }
        }
     …………………..

}    

    /**
     * This is where the invalidate() work actually happens. A full invalidate()
     * causes the drawing cache to be invalidated, but this function can be called with
     * invalidateCache set to false to skip that invalidation step for cases that do not
     * need it (for example, a component that remains at the same dimensions with the same
     * content).
     *
     * @param invalidateCache Whether the drawing cache for this view should be invalidated as
     * well. This is usually true for a full invalidate, but may be set to false if the
     * View‘s contents or dimensions have not changed.
　　　* 指示在视图刷新时，是否也要刷新绘图缓存，对于一个完全的刷新操作，比如视图内容发生了变化，
　　　* 或者控件尺寸发生变化了，那么应该设置true，但是如果不是二者任何一个，则应该设置为false。
     */
    void invalidate(boolean invalidateCache) {
        if (skipInvalidate()) {
            return;
        }
        if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS) ||
                (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) ||
                (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED || isOpaque() != mLastIsOpaque) {
            mLastIsOpaque = isOpaque();
            mPrivateFlags &= ~PFLAG_DRAWN;
            mPrivateFlags |= PFLAG_DIRTY;
            if (invalidateCache) {
                mPrivateFlags |= PFLAG_INVALIDATED;
                mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
            }
            final AttachInfo ai = mAttachInfo;
            final ViewParent p = mParent;
            //noinspection PointlessBooleanExpression,ConstantConditions
            if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
                if (p != null && ai != null && ai.mHardwareAccelerated) {
                    // fast-track for GL-enabled applications; just invalidate the whole hierarchy
                    // with a null dirty rect, which tells the ViewAncestor to redraw everything
                    p.invalidateChild(this, null);
                    return;
                }
            }

            if (p != null && ai != null) {
                final Rect r = ai.mTmpInvalRect;
                r.set(0, 0, mRight - mLeft, mBottom - mTop);
                // Don‘t call invalidate -- we don‘t want to internally scroll
                // our own bounds
                p.invalidateChild(this, r);
            }
        }
    }

    /**
     * Indicates what types of drawing caches should be kept in memory after
     * they have been created.
     *
     * @see #getPersistentDrawingCache()
     * @see #setAnimationCacheEnabled(boolean)
     *
     * @param drawingCacheToKeep one or a combination of {@link #PERSISTENT_NO_CACHE},
     *        {@link #PERSISTENT_ANIMATION_CACHE}, {@link #PERSISTENT_SCROLLING_CACHE}
     *        and {@link #PERSISTENT_ALL_CACHES}
     */
    public void setPersistentDrawingCache(int drawingCacheToKeep) {
        mPersistentDrawingCache = drawingCacheToKeep & PERSISTENT_ALL_CACHES;
    }