Android源码解析之属性动画详解
前言
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大家在日常开发中离不开动画,属性动画更为强大,我们不仅要知道如何使用,更要知道他的原理。这样,才能得心应手。那么,今天,就从最简单的来说,了解下属性动画的原理。
ObjectAnimator .ofInt(mView,"width",100,500) .setDuration(1000) .start();
ObjectAnimator#ofInt
以这个为例,代码如下。
public static ObjectAnimator ofInt(Object target, String propertyName, int... values) { ObjectAnimator anim = new ObjectAnimator(target, propertyName); anim.setIntValues(values); return anim; }
在这个方法中,首先会new一个ObjectAnimator对象,然后通过setIntValues方法将值设置进去,然后返回。在ObjectAnimator的构造方法中,会通过setTarget方法设置当前动画的对象,通过setPropertyName设置当前的属性名。我们重点说下setIntValues方法。
public void setIntValues(int... values) { if (mValues == null || mValues.length == 0) { // No values yet - this animator is being constructed piecemeal. Init the values with // whatever the current propertyName is if (mProperty != null) { setValues(PropertyValuesHolder.ofInt(mProperty, values)); } else { setValues(PropertyValuesHolder.ofInt(mPropertyName, values)); } } else { super.setIntValues(values); } }
首先会判断,mValues是不是null,我们这里是null,并且mProperty也是null,所以会调用setValues(PropertyValuesHolder.ofInt(mPropertyName, values));
方法。先看PropertyValuesHolder.ofInt
方法,PropertyValuesHolder这个类是holds属性和值的,在这个方法会构造一个IntPropertyValuesHolder对象并返回。
public static PropertyValuesHolder ofInt(String propertyName, int... values) { return new IntPropertyValuesHolder(propertyName, values); }
IntPropertyValuesHolder的构造方法如下:
public IntPropertyValuesHolder(String propertyName, int... values) { super(propertyName); setIntValues(values); }
在这里,首先会调用他的分类的构造方法,然后调用setIntValues方法,在他父类的构造方法中,只是设置了下propertyName。setIntValues内容如下:
public void setIntValues(int... values) { super.setIntValues(values); mIntKeyframes = (Keyframes.IntKeyframes) mKeyframes; }
在父类的setIntValues方法中,初始化了mValueType为int.class,mKeyframes为KeyframeSet.ofInt(values)。其中KeyframeSet为关键帧集合。然后将mKeyframes赋值给mIntKeyframes。
KeyframeSet
这个类是记录关键帧的。我们看下他的ofInt方法。
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); }
在这里呢?根据传入的values来计算关键帧,最后返回IntKeyframeSet。
回到ObjectAnimator里面,这里的setValues用的是父类ValueAnimator的
ValueAnimator#setValues
public void setValues(PropertyValuesHolder... values) { int numValues = values.length; mValues = values; mValuesMap = new HashMap(numValues); for (int i = 0; i < numValues; ++i) { PropertyValuesHolder valuesHolder = values[i]; mValuesMap.put(valuesHolder.getPropertyName(), valuesHolder); } // New property/values/target should cause re-initialization prior to starting mInitialized = false; }
这里的操作就简单了,就是把PropertyValuesHolder放入到mValuesMap中。
ObjectAnimator#start
这个方法就是动画开始的地方。
public void start() { // See if any of the current active/pending animators need to be canceled AnimationHandler handler = sAnimationHandler.get(); if (handler != null) { int numAnims = handler.mAnimations.size(); for (int i = numAnims - 1; i >= 0; i--) { if (handler.mAnimations.get(i) instanceof ObjectAnimator) { ObjectAnimator anim = (ObjectAnimator) handler.mAnimations.get(i); if (anim.mAutoCancel && hasSameTargetAndProperties(anim)) { anim.cancel(); } } } numAnims = handler.mPendingAnimations.size(); for (int i = numAnims - 1; i >= 0; i--) { if (handler.mPendingAnimations.get(i) instanceof ObjectAnimator) { ObjectAnimator anim = (ObjectAnimator) handler.mPendingAnimations.get(i); if (anim.mAutoCancel && hasSameTargetAndProperties(anim)) { anim.cancel(); } } } numAnims = handler.mDelayedAnims.size(); for (int i = numAnims - 1; i >= 0; i--) { if (handler.mDelayedAnims.get(i) instanceof ObjectAnimator) { ObjectAnimator anim = (ObjectAnimator) handler.mDelayedAnims.get(i); if (anim.mAutoCancel && hasSameTargetAndProperties(anim)) { anim.cancel(); } } } } if (DBG) { Log.d(LOG_TAG, "Anim target, duration: " + getTarget() + ", " + getDuration()); for (int i = 0; i < mValues.length; ++i) { PropertyValuesHolder pvh = mValues[i]; Log.d(LOG_TAG, " Values[" + i + "]: " + pvh.getPropertyName() + ", " + pvh.mKeyframes.getValue(0) + ", " + pvh.mKeyframes.getValue(1)); } } super.start(); }
首先呢,会获取AnimationHandler对象,如果不为空的话,就会判断是mAnimations、mPendingAnimations、mDelayedAnims中的动画,并且取消。最后调用父类的start方法。
ValueAnimator#start
private void start(boolean playBackwards) { if (Looper.myLooper() == null) { throw new AndroidRuntimeException("Animators may only be run on Looper threads"); } mReversing = playBackwards; mPlayingBackwards = playBackwards; if (playBackwards && mSeekFraction != -1) { if (mSeekFraction == 0 && mCurrentIteration == 0) { // special case: reversing from seek-to-0 should act as if not seeked at all mSeekFraction = 0; } else if (mRepeatCount == INFINITE) { mSeekFraction = 1 - (mSeekFraction % 1); } else { mSeekFraction = 1 + mRepeatCount - (mCurrentIteration + mSeekFraction); } mCurrentIteration = (int) mSeekFraction; mSeekFraction = mSeekFraction % 1; } if (mCurrentIteration > 0 && mRepeatMode == REVERSE && (mCurrentIteration < (mRepeatCount + 1) || mRepeatCount == INFINITE)) { // if we were seeked to some other iteration in a reversing animator, // figure out the correct direction to start playing based on the iteration if (playBackwards) { mPlayingBackwards = (mCurrentIteration % 2) == 0; } else { mPlayingBackwards = (mCurrentIteration % 2) != 0; } } int prevPlayingState = mPlayingState; mPlayingState = STOPPED; mStarted = true; mStartedDelay = false; mPaused = false; updateScaledDuration(); // in case the scale factor has changed since creation time AnimationHandler animationHandler = getOrCreateAnimationHandler(); animationHandler.mPendingAnimations.add(this); if (mStartDelay == 0) { // This sets the initial value of the animation, prior to actually starting it running if (prevPlayingState != SEEKED) { setCurrentPlayTime(0); } mPlayingState = STOPPED; mRunning = true; notifyStartListeners(); } animationHandler.start(); }
- 先初始化一些值
- updateScaledDuration 缩放时间,默认为1.0f
- 获取或者创建AnimationHandler,将动画加入到mPendingAnimations列表中,
- 如果没延迟,通知监听器
- animationHandler.start
在animationHandler.start
中,会调用scheduleAnimation方法,在这个种,会用mChoreographerpost一个callback,最终会执行mAnimate的run方法。mChoreographerpost涉及到VSYNC,这里不多介绍。
mAnimate#run
doAnimationFrame(mChoreographer.getFrameTime());
在这里会用过doAnimationFrame设置动画帧,我们看下这个方法的代码。
void doAnimationFrame(long frameTime) { mLastFrameTime = 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) { ArrayListpendingCopy = (ArrayList ) 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); } } } // Next, process animations currently sitting on the delayed queue, adding // them to the active animations if they are ready int numDelayedAnims = mDelayedAnims.size(); for (int i = 0; i < numDelayedAnims; ++i) { ValueAnimator anim = mDelayedAnims.get(i); if (anim.delayedAnimationFrame(frameTime)) { mReadyAnims.add(anim); } } int numReadyAnims = mReadyAnims.size(); if (numReadyAnims > 0) { for (int i = 0; i < numReadyAnims; ++i) { ValueAnimator anim = mReadyAnims.get(i); anim.startAnimation(this); anim.mRunning = true; mDelayedAnims.remove(anim); } mReadyAnims.clear(); } // Now process all active animations. The return value from animationFrame() // tells the handler whether it should now be ended 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); } } mTmpAnimations.clear(); if (mEndingAnims.size() > 0) { for (int i = 0; i < mEndingAnims.size(); ++i) { mEndingAnims.get(i).endAnimation(this); } mEndingAnims.clear(); } // Schedule final commit for the frame. mChoreographer.postCallback(Choreographer.CALLBACK_COMMIT, mCommit, null); // If there are still active or delayed animations, schedule a future call to // onAnimate to process the next frame of the animations. if (!mAnimations.isEmpty() || !mDelayedAnims.isEmpty()) { scheduleAnimation(); } }
方法较长,逻辑如下:
- 从mPendingAnimations中取出动画,根据事先选择startAnimation还是加入到mDelayedAnims列表。
- 如果mDelayedAnims列表中的动画准备好了,就加入到mReadyAnims列表中
- 从mAnimations列表中取出要执行的动画,加入到mTmpAnimations列表
- 通过doAnimationFrame方法执行动画帧
- 继续执行scheduleAnimation
从上面我们能看出,执行动画的关键是doAnimationFrame方法。在这个方法中,会调用animationFrame方法。
ValueAniator#animationFrame
boolean animationFrame(long currentTime) { boolean done = false; switch (mPlayingState) { case RUNNING: case SEEKED: float fraction = mDuration > 0 ? (float)(currentTime - mStartTime) / mDuration : 1f; if (mDuration == 0 && mRepeatCount != INFINITE) { // Skip to the end mCurrentIteration = mRepeatCount; if (!mReversing) { mPlayingBackwards = false; } } 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; // Note: We do not need to update the value of mStartTimeCommitted here // since we just added a duration offset. } else { done = true; fraction = Math.min(fraction, 1.0f); } } if (mPlayingBackwards) { fraction = 1f - fraction; } animateValue(fraction); break; } return done; }
- 计算fraction
- 调用animateValue方法
根据虚拟机执行引擎动态分派原则,这里会调用ObjectAnimator的animateValue方法。
ObjectAnimator#animateValue
void animateValue(float fraction) { final Object target = getTarget(); if (mTarget != null && target == null) { // We lost the target reference, cancel and clean up. cancel(); return; } super.animateValue(fraction); int numValues = mValues.length; for (int i = 0; i < numValues; ++i) { mValues[i].setAnimatedValue(target); } }
这里主要干了两件事,
- 调用父类的animateValue方法
- 通过setAnimatedValue设置属性
其父类的方法如下:
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); } } }
在这个方法中,会通过Interpolator得到出当前的fraction,并通过calculateValue来计算当前应该的值,这里会调用IntPropertyValuesHolder的calculateValue
void calculateValue(float fraction) { mIntAnimatedValue = mIntKeyframes.getIntValue(fraction); }
我们知道,mIntKeyframes对应的是IntKeyframeSet。在这个类的getIntValue中,会通过TypeEvaluator来计算当前对应的值。不多说了。
最后,回到animateValue。计算了值之后,会调用setAnimatedValue来设置值。我们看看他的实现。
IntPropertyValuesHolder#setAnimatedValue
void setAnimatedValue(Object target) { if (mIntProperty != null) { mIntProperty.setValue(target, mIntAnimatedValue); return; } if (mProperty != null) { mProperty.set(target, mIntAnimatedValue); return; } if (mJniSetter != 0) { nCallIntMethod(target, mJniSetter, mIntAnimatedValue); return; } if (mSetter != null) { try { mTmpValueArray[0] = mIntAnimatedValue; mSetter.invoke(target, mTmpValueArray); } catch (InvocationTargetException e) { Log.e("PropertyValuesHolder", e.toString()); } catch (IllegalAccessException e) { Log.e("PropertyValuesHolder", e.toString()); } } }
恩,到这里就能看到修改属性值得痕迹了,有以下四种情况
- mIntProperty不为null
- mProperty不为null
- mJniSetter不为null
- mSetter不为null
首先,我们通过String propertyName, int… values参数构造的对象,mIntProperty为null,并且mProperty也为null。那其他两个是怎么来的呢?似乎漏了什么?
还节的,在doAnimationFrame中,直接调用startAnimation么?没错,就是这里。
startAnimation
在这个方法中调用了initAnimation方法。还是根据动态分派规则,这里调用ObjectAnimator的initAnimation方法。在这里调用PropertyValuesHolder的setupSetterAndGetter方法,在这里对mSetter等进行了初始化,这里就不多说了,大家自己看代码吧。
好了,以上就是关于Android中属性动画对的全部内容,希望本文的内容对各位Android开发者们能带来一定的帮助,如果有疑问大家可以留言交流,谢谢大家对创新互联的支持。
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