val valueAnimator = ValueAnimator.ofInt(0, 100,300).apply {
duration = 1000
interpolator = LinearInterpolator()
addUpdateListener {
}
}
valueAnimator.start()
问题：
那我们先从ValueAnimator.ofInt()开始分析
//ValueAnimator
public static ValueAnimator ofInt(int... values) {
ValueAnimator anim = new ValueAnimator();
anim.setIntValues(values);
return anim;
}
我们重点是要查看values的去向,进入anim.setFloatValues(value)方法
//ValueAnimator
public void setIntValues(int... values) {
if (values == null || values.length == 0) {
return;
}
if (mValues == null || mValues.length == 0) {
setValues(PropertyValuesHolder.ofInt("", values));
} else {
PropertyValuesHolder valuesHolder = mValues[0];
valuesHolder.setIntValues(values);
}
// New property/values/target should cause re-initialization prior to starting
mInitialized = false;
}
mValues为null，执行setValues(PropertyValuesHolder.ofInt("", values));最终调用了IntPropertyValuesHolder的构造方法
//IntPropertyValuesHolder
public IntPropertyValuesHolder(String propertyName, int... values) {
super(propertyName);
setIntValues(values);
}
//IntPropertyValuesHolder
public void setIntValues(int... values) {
mValueType = int.class;
mKeyframes = KeyframeSet.ofInt(values);
}
这里会生成KeyframeSet
//KeyframeSet
public static KeyframeSet ofInt(int... values) {
int numKeyframes = values.length;
IntKeyframe keyframes[] = new IntKeyframe[Math.max(numKeyframes,2)];
if (numKeyframes == 1) {
keyframes[0] = (IntKeyframe) Keyframe.ofInt(0f);
keyframes[1] = (IntKeyframe) Keyframe.ofInt(1f, values[0]);
} else {
keyframes[0] = (IntKeyframe) Keyframe.ofInt(0f, values[0]);
for (int i = 1; i < numKeyframes; ++i) {
keyframes[i] =
(IntKeyframe) Keyframe.ofInt((float) i / (numKeyframes - 1), values[i]);
}
}
return new IntKeyframeSet(keyframes);
}
这里说明了我们在可变参数传一个的时候为什么动画是从0开始，原来在内部在初始化的时候进行了处理,初始化操作就到这里。
public static Keyframe ofInt(float fraction, int value) {
return new IntKeyframe(fraction, value);
}
/**
* Internal subclass used when the keyframe value is of type int.
*/
static class IntKeyframe extends Keyframe {
/**
* The value of the animation at the time mFraction.
*/
int mValue;
IntKeyframe(float fraction, int value) {
mFraction = fraction;
mValue = value;
mValueType = int.class;
mHasValue = true;
}
}
在创建每个关键帧时，传入了两个参数，第一个参数就是表示这个关键帧在整个区域之间的位置，第二参数就是它表示的值是多少。看上面的代码， i 表示的是第几帧，numKeyframes 表示的是关键帧的总数量，所以 i/(numKeyframes - 1) 也就是表示这一系列关键帧是按等比例来分配的。
到这里对我们前面提出的问题，还是没有解决？
只知道
0是第一帧(fraction = 0)
100是第二帧(fraction = 1/2)
300是第三帧(fraction = 1 )
//IntKeyframeSet
public IntKeyframeSet(IntKeyframe... keyframes) {
super(keyframes);
}
public class KeyframeSet implements Keyframes {
int mNumKeyframes;
Keyframe mFirstKeyframe;
Keyframe mLastKeyframe;
TimeInterpolator mInterpolator; // only used in the 2-keyframe case
List<Keyframe> mKeyframes; // only used when there are not 2 keyframes
TypeEvaluator mEvaluator;
public KeyframeSet(Keyframe... keyframes) {
mNumKeyframes = keyframes.length;
// immutable list
mKeyframes = Arrays.asList(keyframes);
mFirstKeyframe = keyframes[0];
mLastKeyframe = keyframes[mNumKeyframes - 1];
mInterpolator = mLastKeyframe.getInterpolator();
}
ValueAnimator.ofInt流程图
现在ValueAnimator#mValues持有PropertyValuesHolder
PropertyValuesHolder#mKeyframes持有IntKeyframeSet
IntKeyframeSet#mKeyframes持有IntKeyframe
属性动画中什么时候用到了PropertyValuesHolder#mValues
那现在我们从入手valueAnimator.start()，看看什么时候用到了mValues
只能从animator.start()中去寻找答案了
** ps:本次分析的是ValueAnimator，不是ObjectAnimator**
@Override
public void start() {
start(false);
}
private void start(boolean playBackwards) {
if (Looper.myLooper() == null) {
throw new AndroidRuntimeException("Animators may only be run on Looper threads");
}
mReversing = playBackwards;
mSelfPulse = !mSuppressSelfPulseRequested;
// Special case: reversing from seek-to-0 should act as if not seeked at all.
if (playBackwards && mSeekFraction != -1 && mSeekFraction != 0) {
if (mRepeatCount == INFINITE) {
// Calculate the fraction of the current iteration.
float fraction = (float) (mSeekFraction - Math.floor(mSeekFraction));
mSeekFraction = 1 - fraction;
} else {
mSeekFraction = 1 + mRepeatCount - mSeekFraction;
}
}
mStarted = true;
mPaused = false;
mRunning = false;
mAnimationEndRequested = false;
// Resets mLastFrameTime when start() is called, so that if the animation was running,
// calling start() would put the animation in the
// started-but-not-yet-reached-the-first-frame phase.
mLastFrameTime = -1;
mFirstFrameTime = -1;
mStartTime = -1;
addAnimationCallback(0);
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.
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);
}
}
}
调用了内部的 start(boolean) 方法，前面无外乎就是一些变量的初始化，然后好像调用了很多方法，我们知道AnimationHandler是统一处理属性动画的，那么就找和AnimationHandler相关的逻辑。
ok找到了，在addAnimationCallback(0)中，我们找到了和AnimationHandler相关的逻辑，来看看：
private void addAnimationCallback(long delay) {
if (!mSelfPulse) {
return;
}
getAnimationHandler().addAnimationFrameCallback(this, delay);
}
public void addAnimationFrameCallback(final AnimationFrameCallback callback, long delay) {
/**
* 重点
*/
if (mAnimationCallbacks.size() == 0) {
getProvider().postFrameCallback(mFrameCallback);
}
if (!mAnimationCallbacks.contains(callback)) {
mAnimationCallbacks.add(callback);
}
if (delay > 0) {
mDelayedCallbackStartTime.put(callback, (SystemClock.uptimeMillis() + delay));
}
}
//ValueAnimator
private AnimationFrameCallbackProvider getProvider() {
if (mProvider == null) {
mProvider = new MyFrameCallbackProvider();
}
return mProvider;
}
//MyFrameCallbackProvider
public void postFrameCallback(Choreographer.FrameCallback callback) {
mChoreographer.postFrameCallback(callback);
}
看到 Choreographer 了，感觉我们好像已经快接近真相了，不继续跟下去了。
大概说一下后面的流程：
Choreographer 内部有几个队列，通过postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) 方法将FrameCallback放进队列中，callbackType是区分队列类型的，属性动画中传入的是CALLBACK_ANIMATION用于区分这些队列。接着，Choreographer#scheduleFrameLocked()->scheduleFrameLocked#()scheduleVsyncLocked()->FrameDisplayEventReceiver#scheduleVsyncLocked()->最终调用native的方法nativeScheduleVsync（）
向底层注册屏幕监听信号。
nativeScheduleVsync()会向SurfaceFlinger注册Vsync信号的监听，VSync信号由SurfaceFlinger实现并定时发送，当Vsync信号来的时候就会回调FrameDisplayEventReceiver#onVsync()，这个方法给发送一个带时间戳Runnable消息，这个Runnable消息的run()实现就是FrameDisplayEventReceiver# run()， 接着就会执行doFrame()
具体的流程比如：nativeScheduleVsync怎么向SurfaceFlinger注册监听信号，以及SurfaceFlinger和VSync是什么？以后再去研究。
根据目前的信息，我们先小结一下：
当 ValueAnimator 调用了 start() 方法之后，首先会对一些变量进行初始化工作并通知动画开始了，然后 ValueAnimator 实现了 AnimationFrameCallback 接口，并通过 AnimationHander 将自身 this 作为参数传到 mAnimationCallbacks 列表里缓存起来。而 AnimationHandler 在 mAnimationCallbacks 列表大小为 0 时会通过内部类 MyFrameCallbackProvider 将一个 mFrameCallback 工作缓存到 Choreographer 的待执行队列里，并向底层注册监听下一个屏幕刷新信号事件。
当屏幕刷新信号到的时候，Choreographer 的 doFrame() 会去将这些待执行队列里的工作取出来执行，那么此时也就回调了 AnimationHandler 的 mFrameCallback 工作。
那么，接下去就继续看看，当接收到屏幕刷新信号之后，mFrameCallback 又继续做了什么：
private final Choreographer.FrameCallback mFrameCallback = new Choreographer.FrameCallback() {
@Override
public void doFrame(long frameTimeNanos) {
doAnimationFrame(getProvider().getFrameTime());
if (mAnimationCallbacks.size() > 0) {
getProvider().postFrameCallback(this);
}
}
};
那么，下去就是跟着 doAnimationFrame() 来看看，属性动画是怎么执行的
//AnimationHandler
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)) {
callback.doAnimationFrame(frameTime);
if (mCommitCallbacks.contains(callback)) {
getProvider().postCommitCallback(new Runnable() {
@Override
public void run() {
commitAnimationFrame(callback, getProvider().getFrameTime());
}
});
}
}
}
cleanUpList();
}
//ValueAnimator
public final boolean doAnimationFrame(long frameTime) {
if (mStartTime < 0) {
// First frame. If there is start delay, start delay count down will happen *after* this
// frame.
mStartTime = mReversing
? frameTime
: frameTime + (long) (mStartDelay * resolveDurationScale());
}
// Handle pause/resume
if (mPaused) {
mPauseTime = frameTime;
removeAnimationCallback();
return false;
} else if (mResumed) {
mResumed = false;
if (mPauseTime > 0) {
// Offset by the duration that the animation was paused
mStartTime += (frameTime - mPauseTime);
}
}
if (!mRunning) {
// If not running, that means the animation is in the start delay phase of a forward
// running animation. In the case of reversing, we want to run start delay in the end.
if (mStartTime > frameTime && mSeekFraction == -1) {
// This is when no seek fraction is set during start delay. If developers change the
// seek fraction during the delay, animation will start from the seeked position
// right away.
return false;
} else {
// If mRunning is not set by now, that means non-zero start delay,
// no seeking, not reversing. At this point, start delay has passed.
mRunning = true;
startAnimation();
}
}
if (mLastFrameTime < 0) {
if (mSeekFraction >= 0) {
long seekTime = (long) (getScaledDuration() * mSeekFraction);
mStartTime = frameTime - seekTime;
mSeekFraction = -1;
}
mStartTimeCommitted = false; // allow start time to be compensated for jank
}
mLastFrameTime = frameTime;
// 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);
boolean finished = animateBasedOnTime(currentTime);
if (finished) {
endAnimation();
}
return finished;
}
稍微概括一下，这个方法内部其实就做了三件事：
我们重点在第二件事中查找答案：
//ValueAnimator
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);
animateValue(currentIterationFraction);
}
return done;
}
我们首先fraction 是怎么计算的
final float fraction = scaledDuration > 0 ?
(float)(currentTime - mStartTime) / scaledDuration : 1f;
每个动画在处理当前帧的动画逻辑时，首先会先根据当前时间和动画第一帧时间以及动画的持续时长来初步计算出当前帧时动画所处的进度。
//ValueAnimator
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);
}
}
}
mUpdateListeners.get(i).onAnimationUpdate(this); 这是不是我们刚开始给ValueAnimator设置的addUpdateListener。参数也是ValueAnimator,也就是在这个函数中，计算了当前属性动画所属于的区间，和经过的时长，然后通知动画的进度回调
这部分工作主要就是调用了 mValues[i].calculateValue(fraction) 这一行代码来实现，mValues 是一个 PropertyValuesHolder 类型的数组，所以关键就是去看看这个类的 calculateValue() 做了啥：
//PropertyValuesHolder
@Override
void calculateValue(float fraction) {
mIntAnimatedValue = mIntKeyframes.getIntValue(fraction);
}
我们在使用 ValueAnimator 时，注册了动画进度回调，然后在回调里取当前的值时其实也就是取到上面那个 mAnimatedValue 变量的值，而这个变量的值是通过 mKeyframes.getValue() 计算出来的，那么再继续跟进看看：
//KeyframeSet
@Override
public int getIntValue(float fraction) {
if (fraction <= 0f) {
final IntKeyframe prevKeyframe = (IntKeyframe) mKeyframes.get(0);
final IntKeyframe nextKeyframe = (IntKeyframe) mKeyframes.get(1);
int prevValue = prevKeyframe.getIntValue();
int nextValue = nextKeyframe.getIntValue();
float prevFraction = prevKeyframe.getFraction();
float nextFraction = nextKeyframe.getFraction();
final TimeInterpolator interpolator = nextKeyframe.getInterpolator();
if (interpolator != null) {
fraction = interpolator.getInterpolation(fraction);
}
float intervalFraction = (fraction - prevFraction) / (nextFraction - prevFraction);
return mEvaluator == null ?
prevValue + (int)(intervalFraction * (nextValue - prevValue)) :
((Number)mEvaluator.evaluate(intervalFraction, prevValue, nextValue)).
intValue();
} else if (fraction >= 1f) {
final IntKeyframe prevKeyframe = (IntKeyframe) mKeyframes.get(mNumKeyframes - 2);
final IntKeyframe nextKeyframe = (IntKeyframe) mKeyframes.get(mNumKeyframes - 1);
int prevValue = prevKeyframe.getIntValue();
int nextValue = nextKeyframe.getIntValue();
float prevFraction = prevKeyframe.getFraction();
float nextFraction = nextKeyframe.getFraction();
final TimeInterpolator interpolator = nextKeyframe.getInterpolator();
if (interpolator != null) {
fraction = interpolator.getInterpolation(fraction);
}
float intervalFraction = (fraction - prevFraction) / (nextFraction - prevFraction);
return mEvaluator == null ?
prevValue + (int)(intervalFraction * (nextValue - prevValue)) :
((Number)mEvaluator.evaluate(intervalFraction, prevValue, nextValue)).intValue();
}
IntKeyframe prevKeyframe = (IntKeyframe) mKeyframes.get(0);
for (int i = 1; i < mNumKeyframes; ++i) {
IntKeyframe nextKeyframe = (IntKeyframe) mKeyframes.get(i);
if (fraction < nextKeyframe.getFraction()) {
final TimeInterpolator interpolator = nextKeyframe.getInterpolator();
float intervalFraction = (fraction - prevKeyframe.getFraction()) /
(nextKeyframe.getFraction() - prevKeyframe.getFraction());
int prevValue = prevKeyframe.getIntValue();
int nextValue = nextKeyframe.getIntValue();
// Apply interpolator on the proportional duration.
if (interpolator != null) {
intervalFraction = interpolator.getInterpolation(intervalFraction);
}
return mEvaluator == null ?
prevValue + (int)(intervalFraction * (nextValue - prevValue)) :
((Number)mEvaluator.evaluate(intervalFraction, prevValue, nextValue)).
intValue();
}
prevKeyframe = nextKeyframe;
}
// shouldn't get here
return ((Number)mKeyframes.get(mNumKeyframes - 1).getValue()).intValue();
}
ok，在这里就一步一步的取到了我们刚开始看到的值。
当关键帧超过两帧时，分三种情况来处理：
分开来看一下吧，首先是第一帧的处理逻辑：
@Override
public int getIntValue(float fraction) {
/*
* 第一帧的处理
*
*/
if (fraction <= 0f) {
final IntKeyframe prevKeyframe = (IntKeyframe) mKeyframes.get(0);
final IntKeyframe nextKeyframe = (IntKeyframe) mKeyframes.get(1);
int prevValue = prevKeyframe.getIntValue();
int nextValue = nextKeyframe.getIntValue();
float prevFraction = prevKeyframe.getFraction();
float nextFraction = nextKeyframe.getFraction();
final TimeInterpolator interpolator = nextKeyframe.getInterpolator();
if (interpolator != null) {
fraction = interpolator.getInterpolation(fraction);
}
float intervalFraction = (fraction - prevFraction) / (nextFraction - prevFraction);
return mEvaluator == null ?
prevValue + (int)(intervalFraction * (nextValue - prevValue)) :
((Number)mEvaluator.evaluate(intervalFraction, prevValue, nextValue)).
intValue();
}
return ((Number)mKeyframes.get(mNumKeyframes - 1).getValue()).intValue();
}
mEvaluator我们没有设置，为null，走的是 prevValue + (int)(intervalFraction * (nextValue - prevValue)) ；
intervalFraction = (fraction - prevFraction) / (nextFraction - prevFraction); 表示，在这个帧区间内，所占的比例。
因为是第一帧的处理逻辑：
intervalFraction = (fraction - prevFraction) / (nextFraction - prevFraction);
intervalFraction = 0
第一帧是 prevValue，也就是我们刚开始设置的值（ofInt(0,100,300)）中的0。
@Override
public int getIntValue(float fraction) {
/*
* 中间帧的处理
*
*/
for (int i = 1; i < mNumKeyframes; ++i) {
IntKeyframe nextKeyframe = (IntKeyframe) mKeyframes.get(i);
if (fraction < nextKeyframe.getFraction()) {
final TimeInterpolator interpolator = nextKeyframe.getInterpolator();
float intervalFraction = (fraction - prevKeyframe.getFraction()) /
(nextKeyframe.getFraction() - prevKeyframe.getFraction());
int prevValue = prevKeyframe.getIntValue();
int nextValue = nextKeyframe.getIntValue();
// Apply interpolator on the proportional duration.
if (interpolator != null) {
intervalFraction = interpolator.getInterpolation(intervalFraction);
}
return mEvaluator == null ?
prevValue + (int)(intervalFraction * (nextValue - prevValue)) :
((Number)mEvaluator.evaluate(intervalFraction, prevValue, nextValue)).
intValue();
}
prevKeyframe = nextKeyframe;
}
// shouldn't get here
return ((Number)mKeyframes.get(mNumKeyframes - 1).getValue()).intValue();
}
处理中间帧的逻辑：关键找出当前进度处于哪两个关键帧之间：
从第一帧开始，按顺序遍历每一帧，然后去判断当前的动画进度跟这一帧保存的位置信息来找出当前进度是否就是落在某两个关键帧之间。
至此，我们已经将整个流程梳理出来了，两部分小结的内容整合起来就是这次梳理出来的整个属性动画从 start() 之后，到我们在 onAnimationUpdate 回调中取到我们需要的值。
OK～～～～～
结束了
回答刚开始提出的问题
ValueAnimator时序图结尾：
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