注意Animator并没有自己的thread， 而是使用start 它的thread， 只是有一个自己的可以向该thread post 的 handler罢了
* The animation started by calling this method will be run on the thread that called
* this method. This thread should have a Looper on it. Also, if the animation will animate
* properties of objects in the view hierarchy, then the calling thread should be the UI
* thread for that view hierarchy
private void start(boolean playBackwards) {
if (Looper.myLooper() == null) {
throw new AndroidRuntimeException("Animators may only be run on Looper threads");
}
mPlayingBackwards = playBackwards;
mCurrentIteration = 0;
mPlayingState = STOPPED;
mStarted = true;
mStartedDelay = false;
mPaused = false;
AnimationHandler animationHandler = getOrCreateAnimationHandler();
animationHandler.mPendingAnimations.add(this);
if (mStartDelay == 0) {
// This sets the initial value of the animation, prior to actually starting it running
setCurrentPlayTime(0);
mPlayingState = STOPPED;
mRunning = true;
notifyStartListeners();
}
animationHandler.start();
}
private static AnimationHandler getOrCreateAnimationHandler() {
AnimationHandler handler = sAnimationHandler.get();
if (handler == null) {
handler = new AnimationHandler();
sAnimationHandler.set(handler);
}
return handler;
}
protected static ThreadLocal<AnimationHandler> sAnimationHandler =
new ThreadLocal<AnimationHandler>();
protected static class AnimationHandler implements Runnable {
..................................
private AnimationHandler() {
mChoreographer = Choreographer.getInstance();
}
..................................
public void start() {
scheduleAnimation();
}
..................................
private void scheduleAnimation() {
if (!mAnimationScheduled) {
mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, this, null);
mAnimationScheduled = true;
}
}
.................................
// Called by the Choreographer.
@Override
public void run() {
mAnimationScheduled = false;
doAnimationFrame(mChoreographer.getFrameTime());
}
.................................
private void doAnimationFrame(long frameTime) {
// mPendingAnimations holds any animations that have requested to be started
// We're going to clear mPendingAnimations, but starting animation may
// cause more to be added to the pending list (for example, if one animation
// starting triggers another starting). So we loop until mPendingAnimations
// is empty.
while (mPendingAnimations.size() > 0) {
ArrayList<ValueAnimator> pendingCopy =
(ArrayList<ValueAnimator>) mPendingAnimations.clone();
mPendingAnimations.clear();
int count = pendingCopy.size();
for (int i = 0; i < count; ++i) {
ValueAnimator anim = pendingCopy.get(i);
// If the animation has a startDelay, place it on the delayed list
if (anim.mStartDelay == 0) {
anim.startAnimation(this);
} else {
mDelayedAnims.add(anim);
}
}
}
........................................................
int numAnims = mAnimations.size();
for (int i = 0; i < numAnims; ++i) {
mTmpAnimations.add(mAnimations.get(i));
}
for (int i = 0; i < numAnims; ++i) {
ValueAnimator anim = mTmpAnimations.get(i);
if (mAnimations.contains(anim) && anim.doAnimationFrame(frameTime)) {
mEndingAnims.add(anim);
}
}
...........................................................
if (!mAnimations.isEmpty() || !mDelayedAnims.isEmpty()) {
scheduleAnimation();
}
}
}
...............................................................
private void startAnimation(AnimationHandler handler) {
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, getNameForTrace(),
System.identityHashCode(this));
}
initAnimation();
handler.mAnimations.add(this);
if (mStartDelay > 0 && mListeners != null) {
// Listeners were already notified in start() if startDelay is 0; this is
// just for delayed animations
notifyStartListeners();
}
}
/**
* Processes a frame of the animation, adjusting the start time if needed.
*
* @param frameTime The frame time.
* @return true if the animation has ended.
*/
final boolean doAnimationFrame(long frameTime) {
if (mPlayingState == STOPPED) {
mPlayingState = RUNNING;
if (mSeekTime < 0) {
mStartTime = frameTime;
} else {
mStartTime = frameTime - mSeekTime;
// Now that we're playing, reset the seek time
mSeekTime = -1;
}
}
if (mPaused) {
if (mPauseTime < 0) {
mPauseTime = frameTime;
}
return false;
} else if (mResumed) {
mResumed = false;
if (mPauseTime > 0) {
// Offset by the duration that the animation was paused
mStartTime += (frameTime - mPauseTime);
}
}
// The frame time might be before the start time during the first frame of
// an animation. The "current time" must always be on or after the start
// time to avoid animating frames at negative time intervals. In practice, this
// is very rare and only happens when seeking backwards.
final long currentTime = Math.max(frameTime, mStartTime);
return animationFrame(currentTime);
}
/**
* This internal function processes a single animation frame for a given animation. The
* currentTime parameter is the timing pulse sent by the handler, used to calculate the
* elapsed duration, and therefore
* the elapsed fraction, of the animation. The return value indicates whether the animation
* should be ended (which happens when the elapsed time of the animation exceeds the
* animation's duration, including the repeatCount).
*
* @param currentTime The current time, as tracked by the static timing handler
* @return true if the animation's duration, including any repetitions due to
* <code>repeatCount</code>, has been exceeded and the animation should be ended.
*/
boolean animationFrame(long currentTime) {
boolean done = false;
switch (mPlayingState) {
case RUNNING:
case SEEKED:
float fraction = mDuration > 0 ? (float)(currentTime - mStartTime) / mDuration : 1f;
if (fraction >= 1f) {
if (mCurrentIteration < mRepeatCount || mRepeatCount == INFINITE) {
// Time to repeat
if (mListeners != null) {
int numListeners = mListeners.size();
for (int i = 0; i < numListeners; ++i) {
mListeners.get(i).onAnimationRepeat(this);
}
}
if (mRepeatMode == REVERSE) {
mPlayingBackwards = !mPlayingBackwards;
}
mCurrentIteration += (int)fraction;
fraction = fraction % 1f;
mStartTime += mDuration;
} else {
done = true;
fraction = Math.min(fraction, 1.0f);
}
}
if (mPlayingBackwards) {
fraction = 1f - fraction;
}
animateValue(fraction);
break;
}
return done;
}
/**
* This method is called with the elapsed fraction of the animation during every
* animation frame. This function turns the elapsed fraction into an interpolated fraction
* and then into an animated value (from the evaluator. The function is called mostly during
* animation updates, but it is also called when the <code>end()</code>
* function is called, to set the final value on the property.
*
* <p>Overrides of this method must call the superclass to perform the calculation
* of the animated value.</p>
*
* @param fraction The elapsed fraction of the animation.
*/
void animateValue(float fraction) {
fraction = mInterpolator.getInterpolation(fraction);
mCurrentFraction = fraction;
int numValues = mValues.length;
for (int i = 0; i < numValues; ++i) {
mValues[i].calculateValue(fraction);
}
if (mUpdateListeners != null) {
int numListeners = mUpdateListeners.size();
for (int i = 0; i < numListeners; ++i) {
mUpdateListeners.get(i).onAnimationUpdate(this);
}
}
}
1.ValueAnimator->start():
取得一个ThreadLocal的Runnable（animationHandler），里面封存了一些关于本animator的信息，然后animationHandler.start()
2.AnimationHandler->start()->scheduleAnimation()->mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, this, null):
<这里的CALLBACK_ANIMATION TASK， 其优先级在Choreographer中低于CALLBACK_INPUT， 高于CALLBACK_TRAVERSAL，所以可以认为对于android的每一帧
动画是被优先运行的，动画全部处理完了以后，才会轮到measure layout draw>
将自己schedule给Choreographer，让Choreographer在合适的时机回调自己。（注意，Choreographer的回调是跑在UI-thread）
3.被运行起来时： AnimationHandler->doAnimationFrame(mChoreographer.getFrameTime())
->anim.startAnimation(this)首先把还没有真正start的animator start一边，调用其start回调
->对于已经在run的animator: anim.doAnimationFrame(frameTime), 这个函数里就是一系列的调整值，并调用相应的update回调。
->
if (!mAnimations.isEmpty() || !mDelayedAnims.isEmpty()) { scheduleAnimation();
} 如果还有没有run完的animator，那么就继续将自己schedule给Choreographer，等待下一次的回调.
顺便看了下Aniamtion的原理，Animation和Animator不同，Animation通过在View的draw()中调用了drawAnimation()来实现效果.
有一点注意:
2.x系列不支持Animator,因为这是后来才引入的，不过可以用nineoldandroids这个库来模拟实现，原理差不过，只不过2.x没有Choreographer，因此调度时会有差别.
