ValueAnimator源码解析-基于Android API3

时序图.png

先上个时序图，整个调用链都在图里了。

源码

ValueAnimator.java

    public void start() {
        start(false);
    }

private void start(boolean playBackwards) {
        //所以在线程中执行时必须得Looper.prepare（）
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
       ...省略
        addAnimationCallback(0);
        //如果不延迟启动
        if (mStartDelay == 0 || mSeekFraction >= 0 || mReversing) {
            // If there's no start delay, init the animation and notify start listeners right away
            // to be consistent with the previous behavior. Otherwise, postpone this until the first
            // frame after the start delay.
            //开始动画，回调动画开始了
            startAnimation();
            if (mSeekFraction == -1) {
                // No seek, start at play time 0. Note that the reason we are not using fraction 0
                // is because for animations with 0 duration, we want to be consistent with pre-N
                // behavior: skip to the final value immediately.
                setCurrentPlayTime(0);
            } else {
                setCurrentFraction(mSeekFraction);
            }
        }
    }

    private void addAnimationCallback(long delay) {
        if (!mSelfPulse) {
            return;
        }
        getAnimationHandler().addAnimationFrameCallback(this, delay);
    }

    public AnimationHandler getAnimationHandler() {
        return mAnimationHandler != null ? mAnimationHandler : AnimationHandler.getInstance();
    }

初始化动画，并将监听添加到AnimationHandler

AnimationHandler.java

    private final Choreographer.FrameCallback mFrameCallback = new Choreographer.FrameCallback() {
        @Override
        public void doFrame(long frameTimeNanos) {
            doAnimationFrame(getProvider().getFrameTime());
            //动画回调不为空，继续请求信号量
            if (mAnimationCallbacks.size() > 0) {
                getProvider().postFrameCallback(this);
            }
        }
    };

    public void addAnimationFrameCallback(final AnimationFrameCallback callback, long delay) {
        if (mAnimationCallbacks.size() == 0) {
            //Frame监听
            getProvider().postFrameCallback(mFrameCallback);
        }
        if (!mAnimationCallbacks.contains(callback)) {
            //动画回调
            mAnimationCallbacks.add(callback);
        }

        if (delay > 0) {
            //延迟
            mDelayedCallbackStartTime.put(callback, (SystemClock.uptimeMillis() + delay));
        }
    }

    private AnimationFrameCallbackProvider getProvider() {
        if (mProvider == null) {
            mProvider = new MyFrameCallbackProvider();
        }
        return mProvider;
    }

    private class MyFrameCallbackProvider implements AnimationFrameCallbackProvider {

        final Choreographer mChoreographer = Choreographer.getInstance();

        @Override
        public void postFrameCallback(Choreographer.FrameCallback callback) {
            //添加Frame监听
            mChoreographer.postFrameCallback(callback);
        }

        @Override
        public void postCommitCallback(Runnable runnable) {
            mChoreographer.postCallback(Choreographer.CALLBACK_COMMIT, runnable, null);
        }

        @Override
        public long getFrameTime() {
            return mChoreographer.getFrameTime();
        }

        @Override
        public long getFrameDelay() {
            return Choreographer.getFrameDelay();
        }

        @Override
        public void setFrameDelay(long delay) {
            Choreographer.setFrameDelay(delay);
        }
    }

将Frame监听添加到Choreographer

Choreographer.java

    public void postFrameCallback(FrameCallback callback) {
        postFrameCallbackDelayed(callback, 0);
    }
    public void postFrameCallbackDelayed(FrameCallback callback, long delayMillis) {
        if (callback == null) {
            throw new IllegalArgumentException("callback must not be null");
        }

        postCallbackDelayedInternal(CALLBACK_ANIMATION,
                callback, FRAME_CALLBACK_TOKEN, delayMillis);
    }


    private void postCallbackDelayedInternal(int callbackType,
            Object action, Object token, long delayMillis) {
        if (DEBUG_FRAMES) {
            Log.d(TAG, "PostCallback: type=" + callbackType
                    + ", action=" + action + ", token=" + token
                    + ", delayMillis=" + delayMillis);
        }

        synchronized (mLock) {
             ...省略
            scheduleFrameLocked(now);
        }
    }

    private void scheduleFrameLocked(long now) {
        if (!mFrameScheduled) {
            mFrameScheduled = true;
            if (USE_VSYNC) {
                if (DEBUG_FRAMES) {
                    Log.d(TAG, "Scheduling next frame on vsync.");
                }

                //是否在主线程，如果没有在主线程则发送同步消息，最终还是会执行scheduleVsyncLocked
                if (isRunningOnLooperThreadLocked()) {
                    scheduleVsyncLocked();
                } else {
                    Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_VSYNC);
                    msg.setAsynchronous(true);
                    mHandler.sendMessageAtFrontOfQueue(msg);
                }
            } else {
                final long nextFrameTime = Math.max(
                        mLastFrameTimeNanos / TimeUtils.NANOS_PER_MS + sFrameDelay, now);
                if (DEBUG_FRAMES) {
                    Log.d(TAG, "Scheduling next frame in " + (nextFrameTime - now) + " ms.");
                }
                Message msg = mHandler.obtainMessage(MSG_DO_FRAME);
                msg.setAsynchronous(true);
                mHandler.sendMessageAtTime(msg, nextFrameTime);
            }
        }
    }
    
    private void scheduleVsyncLocked() {
        //请求下一个信号
        mDisplayEventReceiver.scheduleVsync();
    }

请求下一个信号，不明白信号的可看《Android 底层渲染 - 屏幕刷新机制源码分析》

FrameDisplayEventReceiver.java

private final class FrameDisplayEventReceiver extends DisplayEventReceiver
            implements Runnable {
        private boolean mHavePendingVsync;
        private long mTimestampNanos;
        private int mFrame;

        public FrameDisplayEventReceiver(Looper looper, int vsyncSource) {
            super(looper, vsyncSource, CONFIG_CHANGED_EVENT_SUPPRESS);
        }

        //信号来了处理
        @Override
        public void onVsync(long timestampNanos, long physicalDisplayId, int frame) {
            // Post the vsync event to the Handler.
            // The idea is to prevent incoming vsync events from completely starving
            // the message queue.  If there are no messages in the queue with timestamps
            // earlier than the frame time, then the vsync event will be processed immediately.
            // Otherwise, messages that predate the vsync event will be handled first.
            long now = System.nanoTime();
            if (timestampNanos > now) {
                Log.w(TAG, "Frame time is " + ((timestampNanos - now) * 0.000001f)
                        + " ms in the future!  Check that graphics HAL is generating vsync "
                        + "timestamps using the correct timebase.");
                timestampNanos = now;
            }

            if (mHavePendingVsync) {
                Log.w(TAG, "Already have a pending vsync event.  There should only be "
                        + "one at a time.");
            } else {
                mHavePendingVsync = true;
            }
            //handler发送同步消息，message的callback就是FrameDisplayEventReceiver
            mTimestampNanos = timestampNanos;
            mFrame = frame;
            Message msg = Message.obtain(mHandler, this);
            msg.setAsynchronous(true);
            mHandler.sendMessageAtTime(msg, timestampNanos / TimeUtils.NANOS_PER_MS);
        }

        @Override
        public void run() {
            //handler执行
            mHavePendingVsync = false;
            doFrame(mTimestampNanos, mFrame);
        }
    }

当来了信号量后，执行onvsync，发送Handler同步消息，Message的Callback就是FrameDisplayEventReceiver，最终通过Handler执行了FrameDisplayEventReceiver.run()方法

DisplayEventReceiver.java

    public void scheduleVsync() {
        if (mReceiverPtr == 0) {
            Log.w(TAG, "Attempted to schedule a vertical sync pulse but the display event "
                    + "receiver has already been disposed.");
        } else {
            nativeScheduleVsync(mReceiverPtr);
        }
    }
    private static native void nativeScheduleVsync(long receiverPtr);
    //分发信号量
    private void dispatchVsync(long timestampNanos, long physicalDisplayId, int frame) {
        onVsync(timestampNanos, physicalDisplayId, frame);
    }

请求信号量，并分发处理

FrameDisplayEventReceiver.java

void doFrame(long frameTimeNanos, int frame) {
        final long startNanos;
        synchronized (mLock) {
        ...省略
        try {
            ...省略
            doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
           ...省略
        } finally {
            AnimationUtils.unlockAnimationClock();
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }

        if (DEBUG_FRAMES) {
            final long endNanos = System.nanoTime();
            Log.d(TAG, "Frame " + frame + ": Finished, took "
                    + (endNanos - startNanos) * 0.000001f + " ms, latency "
                    + (startNanos - frameTimeNanos) * 0.000001f + " ms.");
        }
    }

    void doCallbacks(int callbackType, long frameTimeNanos) {
        CallbackRecord callbacks;
       ...省略
        try {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, CALLBACK_TRACE_TITLES[callbackType]);
            for (CallbackRecord c = callbacks; c != null; c = c.next) {
                if (DEBUG_FRAMES) {
                    Log.d(TAG, "RunCallback: type=" + callbackType
                            + ", action=" + c.action + ", token=" + c.token
                            + ", latencyMillis=" + (SystemClock.uptimeMillis() - c.dueTime));
                }
                c.run(frameTimeNanos);
            }
        } finally {  
            回收CallbackRecord，和Handler回收Message类似
            synchronized (mLock) {
                mCallbacksRunning = false;
                do {
                    final CallbackRecord next = callbacks.next;
                    recycleCallbackLocked(callbacks);
                    callbacks = next;
                } while (callbacks != null);
            }
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }

处理回调
Choreographer.CallbackRecord.java

    private static final class CallbackRecord {
        public CallbackRecord next;
        public long dueTime;
        public Object action; // Runnable or FrameCallback
        public Object token;

        @UnsupportedAppUsage
        public void run(long frameTimeNanos) {
            if (token == FRAME_CALLBACK_TOKEN) {
                //执行Frame回调
                ((FrameCallback)action).doFrame(frameTimeNanos);
            } else {
                ((Runnable)action).run();
            }
        }
    }

执行Frame回调

AnimationHandler.java

    private final Choreographer.FrameCallback mFrameCallback = new Choreographer.FrameCallback() {
        @Override
        public void doFrame(long frameTimeNanos) {
            doAnimationFrame(getProvider().getFrameTime());
            if (mAnimationCallbacks.size() > 0) {
                getProvider().postFrameCallback(this);
            }
        }
    };

    private void doAnimationFrame(long frameTime) {
        long currentTime = SystemClock.uptimeMillis();
        final int size = mAnimationCallbacks.size();
        for (int i = 0; i < size; i++) {
            final AnimationFrameCallback callback = mAnimationCallbacks.get(i);
            if (callback == null) {
                continue;
            }
            if (isCallbackDue(callback, currentTime)) {
                //动画回调
                callback.doAnimationFrame(frameTime);
            }
        }
        cleanUpList();
    }

帧回调到动画回调
ValueAnimator.java

    public final boolean doAnimationFrame(long frameTime) {
        ...省略
        boolean finished = animateBasedOnTime(currentTime);

        if (finished) {
            endAnimation();
        }
        return finished;
    }

    boolean animateBasedOnTime(long currentTime) {
        boolean done = false;
        if (mRunning) {
            final long scaledDuration = getScaledDuration();
            final float fraction = scaledDuration > 0 ?
                    (float)(currentTime - mStartTime) / scaledDuration : 1f;
            final float lastFraction = mOverallFraction;
            final boolean newIteration = (int) fraction > (int) lastFraction;
            final boolean lastIterationFinished = (fraction >= mRepeatCount + 1) &&
                    (mRepeatCount != INFINITE);
            if (scaledDuration == 0) {
                // 0 duration animator, ignore the repeat count and skip to the end
                done = true;
            } else if (newIteration && !lastIterationFinished) {
                // Time to repeat
                if (mListeners != null) {
                    int numListeners = mListeners.size();
                    for (int i = 0; i < numListeners; ++i) {
                        mListeners.get(i).onAnimationRepeat(this);
                    }
                }
            } else if (lastIterationFinished) {
                done = true;
            }
            mOverallFraction = clampFraction(fraction);
            float currentIterationFraction = getCurrentIterationFraction(
                    mOverallFraction, mReversing);
            //当前进度
            animateValue(currentIterationFraction);
        }
        return done;
    }

    void animateValue(float fraction) {
        fraction = mInterpolator.getInterpolation(fraction);
        mCurrentFraction = fraction;
        int numValues = mValues.length;
        for (int i = 0; i < numValues; ++i) {
            //计算值
            mValues[i].calculateValue(fraction);
        }
        if (mUpdateListeners != null) {
            int numListeners = mUpdateListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                //回调
                mUpdateListeners.get(i).onAnimationUpdate(this);
            }
        }
    }

    //结束动画
    private void endAnimation() {
        if (mAnimationEndRequested) {
            return;
        }
        //移除动画监听，所以再也不会有帧相关的计时监听
        removeAnimationCallback();

        mAnimationEndRequested = true;
        mPaused = false;
        boolean notify = (mStarted || mRunning) && mListeners != null;
        if (notify && !mRunning) {
            // If it's not yet running, then start listeners weren't called. Call them now.
            notifyStartListeners();
        }
        mRunning = false;
        mStarted = false;
        mStartListenersCalled = false;
        mLastFrameTime = -1;
        mFirstFrameTime = -1;
        mStartTime = -1;
        if (notify && mListeners != null) {
            ArrayList<AnimatorListener> tmpListeners =
                    (ArrayList<AnimatorListener>) mListeners.clone();
            int numListeners = tmpListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                tmpListeners.get(i).onAnimationEnd(this, mReversing);
            }
        }
        // mReversing needs to be reset *after* notifying the listeners for the end callbacks.
        mReversing = false;
        if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
            Trace.asyncTraceEnd(Trace.TRACE_TAG_VIEW, getNameForTrace(),
                    System.identityHashCode(this));
        }
    }

整个流程就分析完了。动画的核心驱动是，利用屏幕的刷新机制，请求信号，然后在通过Handler的同步消息，执行Frame回调。Frame回调中在执行动画回调。动画回调中根据时间和动画插值。计算出最新的动画值，回调给用户。ValueAnimation中animateBasedOnTime方法会返回当前动画是否结束，如果已经结束就移除动画回调，如果未结束FrameCallback的doFrame中处理完这一帧后，会继续请求下一个信号量。