Android動畫機制源碼分析(待完善)

Android動畫機制源碼分析(待完善)

本文着重講解Android3.0後推出的屬性動畫框架Property Animation——Animator的相關源碼分析

概述

3.0之前已有的動畫框架——Animation存在一些侷限性， Animation框架定義了透明度，旋轉，縮放和位移幾種常見的動畫，而且控制的是整個View，實現原理是每次繪製視圖時View所在的ViewGroup中的drawChild函數獲取該View的Animation的Transformation值，然後調用canvas.concat(transformToApply.getMatrix())，通過矩陣運算完成動畫幀，如果動畫沒有完成，繼續調用invalidate()函數，啓動下次繪製來驅動動畫，動畫過程中的幀之間間隙時間是繪製函數所消耗的時間，可能會導致動畫消耗比較多的CPU資源，最重要的是，動畫改變的只是顯示，並不能改變相應事件作用的位置。3.0之前的動畫我們一般稱爲View動畫.

而在Animator框架中使用最多的是AnimatorSet和ObjectAnimator配合，使用ObjectAnimator進行更精細化控制，只控制一個對象的一個屬性值，多個ObjectAnimator組合到AnimatorSet形成一個動畫。而且ObjectAnimator能夠自動驅動，可以調用setFrameDelay(longframeDelay)設置動畫幀之間的間隙時間，調整幀率，減少動畫過程中頻繁繪製界面，而在不影響動畫效果的前提下減少CPU資源消耗。因此，Anroid推出的強大的屬性動畫框架，基本可以實現所有的動畫效果。

簡單實例

在分析源碼之前先列出幾個常用的實例.後面的源碼分析也會用到其中的實例.

實例1:監聽動畫的過程

public void changMultiplePropertyByValueAnimator(final View v) { 
	RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) v
			.getLayoutParams();
	PropertyValuesHolder pvh_left = PropertyValuesHolder.ofFloat(
			"margin_left", params.leftMargin, 500);
	PropertyValuesHolder pvh_top = PropertyValuesHolder.ofFloat(
			"margin_top", params.topMargin, 500);
	ValueAnimator ani = ValueAnimator.ofPropertyValuesHolder(pvh_left,
			pvh_top).setDuration(1000);
	ani.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
		@Override
		public void onAnimationUpdate(ValueAnimator valueAnimator) {
			float margin_left = (Float) valueAnimator
					.getAnimatedValue("margin_left");
			float margin_top = (Float) valueAnimator
					.getAnimatedValue("margin_top");
			RelativeLayout.LayoutParams p = (LayoutParams) v.getLayoutParams();
			p.leftMargin = (int) margin_left;
			p.topMargin = (int) margin_top;
			v.setLayoutParams(p);
		}
	});
	ani.start();
}

實例2:使用ObjectAnimator動畫改變背景色

/**
 * 使用ObjectAnimator直接設置屬性和值
 */
public void changOneProperty(View v) {
	ValueAnimator colorAnimator = ObjectAnimator.ofInt(v,
			"backgroundColor", 0xffff8080 /*red*/ , 0xff8080ff /*Blue*/ );
	colorAnimator.setDuration(1000);
	colorAnimator.setEvaluator(new ArgbEvaluator());
	colorAnimator.setRepeatCount(ValueAnimator.INFINITE);
	colorAnimator.setRepeatMode(ValueAnimator.REVERSE);// ValueAnimator.RESTART
	colorAnimator.start();
}

實例3:使用AnimatorSet改變多個屬性.

public void changMultiplePropertyByValueAnimator2(View v) {
	/**
	 * 支持屬性: translationX and translationY: These properties control where
	 * the View is located as a delta from its left and top coordinates
	 * which are set by its layout container.
	 * 
	 * rotation, rotationX, and rotationY: These properties control the
	 * rotation in 2D (rotation property) and 3D around the pivot point.
	 * 
	 * scaleX and scaleY: These properties control the 2D scaling of a View
	 * around its pivot point.
	 * 
	 * pivotX and pivotY: These properties control the location of the pivot
	 * point, around which the rotation and scaling transforms occur. By
	 * default, the pivot point is located at the center of the object.
	 * 
	 * x and y: These are simple utility properties to describe the final
	 * location of the View in its container, as a sum of the left and top
	 * values and translationX and translationY values.
	 * 
	 * alpha: Represents the alpha transparency on the View. This value is 1
	 * (opaque) by default, with a value of 0 representing full transparency
	 * (not visible).
	 */
	AnimatorSet set = new AnimatorSet();
	set.playTogether(
			ObjectAnimator.ofFloat(v, "rotation", 0, -90f),
			ObjectAnimator.ofFloat(v, "rotationX", 0, 360f),
			ObjectAnimator.ofFloat(v, "rotationY", 0, 360f),
			ObjectAnimator.ofFloat(v, "translationX", 0, 200f),
			ObjectAnimator.ofFloat(v, "translationY", 0, 200f),
			ObjectAnimator.ofFloat(v, "scalY", 1, 1.5f),
			ObjectAnimator.ofFloat(v, "scalX", 1, 2.0f),
			ObjectAnimator.ofFloat(v, "alpan", 1, 0.25f, 1),
			ObjectAnimator.ofFloat(v, "translationY", 0, 200f));
	//set.playSequentially(animator1,animator2,animator3);
	//set.play(ObjectAnimator.ofFloat(v, "rotation", 0, -90f)).with(anim)
	set.setDuration(1000);
	set.start();
}

實例4:使用PropertyValuesHolder和ObjectAnimator改變多個屬性.

/**
 * 使用PropertyValuesHolder: scal alpha
 * @param view
 */
public void propertyValuesHolder(View view) {
	PropertyValuesHolder pvhX = PropertyValuesHolder.ofFloat("alpha", 1f,0f, 1f);
	PropertyValuesHolder pvhY = PropertyValuesHolder.ofFloat("scaleX", 1f,0, 1f);
	PropertyValuesHolder pvhZ = PropertyValuesHolder.ofFloat("scaleY", 1f,0, 1f);
	PropertyValuesHolder pvhColor = PropertyValuesHolder.ofInt("backgroundColor", 0xffff8080,0xff8080ff, 0xffff8080);
	ObjectAnimator.ofPropertyValuesHolder(view, pvhX, pvhY, pvhZ,pvhColor)
			.setDuration(1000).start();
}

實例5:寫包裝類爲不具有get/set方法的屬性提供修改方法

private static class ViewWrapper {
	private View mTarget;
	public ViewWrapper(View target) {
		mTarget = target;
	}
	public int getWidth() {
		Log.d("ViewWrapper","getWidth");
		return mTarget.getLayoutParams().width;
	}
	public void setWidth(int width) {
		Log.d("ViewWrapper","setWidth");
		mTarget.getLayoutParams().width = width;
		mTarget.requestLayout();
	}
}
public void addProperty(View v){
	ViewWrapper wrapper = new ViewWrapper(v);
	ObjectAnimator.ofInt(wrapper, "width", 500).setDuration(5000).start();
}

對於一個View ,如果想要用屬性動畫,那個屬性就要對於set方法,比如設置的屬性是aaa,那麼我們就要在這個View裏面添加setAaa()方法,這個對自定義的view做動畫效果時很方便.

上面的幾個實例是平時常用到的幾種簡單實例.主要是對ObjectAnimator和PropertyValuesHolder的使用,其中ValueAnimator是ValueAnimator的父類.

源碼分析

分析源碼之前先列出幾個主要的類

ValueAnimator

ObjectAnimator

PropertyValuesHolder

其中, ObjectAnimator 是ValueAnimator 的子類. PropertyValuesHolder還有2個內部靜態子類

FloatPropertyValuesHolder和IntPropertyValuesHolder

後續的源碼分析就以上面的實例4爲參考,同時相關分析是基於Android 5 的源碼

public void propertyValuesHolder(View view) {
	PropertyValuesHolder pvhX = PropertyValuesHolder.ofFloat("alpha", 1f,0f, 1f);
	PropertyValuesHolder pvhY = PropertyValuesHolder.ofFloat("scaleX", 1f,0, 1f);
	PropertyValuesHolder pvhZ = PropertyValuesHolder.ofFloat("scaleY", 1f,0, 1f);
	PropertyValuesHolder pvhColor = PropertyValuesHolder.ofInt("backgroundColor", 0xffff8080,0xff8080ff, 0xffff8080);
	ObjectAnimator.ofPropertyValuesHolder(view, pvhX, pvhY, pvhZ,pvhColor)
			.setDuration(1000).start();
}

上面的第2行調用了PropertyValuesHolder的.ofFloat(),第5行調用了ofInt().這2個方法其實會分別創建一個FloatPropertyValuesHolder和IntPropertyValuesHolder.同時將全部的參數也都傳遞給FloatPropertyValuesHolder和IntPropertyValuesHolder.

public static PropertyValuesHolder ofInt(String propertyName, int... values) {
	return new IntPropertyValuesHolder(propertyName, values);
}

public static PropertyValuesHolder ofFloat(String propertyName, float... values) {
	return new FloatPropertyValuesHolder(propertyName, values);
}

這裏只看一下FloatPropertyValuesHolder 的實現.

public FloatPropertyValuesHolder(String propertyName, float... values) {
	super(propertyName);
	setFloatValues(values);
}

@Override
public void setFloatValues(float... values) {
	super.setFloatValues(values);
	mFloatKeyframes = (Keyframes.FloatKeyframes) mKeyframes;
}

從上面的代碼可以看到FloatPropertyValuesHolder 的構造函數調用其父類的構造函數並調用自己的setFloatValues()方法.其父類的構造函數

PropertyValuesHolder()將屬性名稱記錄在了PropertyValuesHolder 的成員變量mPropertyName裏面.

setFloatValues也會先調用它父類的這個方法,它父類的這個方法會將前面傳遞進來的參數類型保存在變量mValueType裏面,同時根據這些參數生成動畫效果的關鍵幀.如果插入的是float類型的參數生成mKeyframes就是FloatKeyframeSet,int類型對應的就是IntKeyframeSet, FloatKeyframeSet和IntKeyframeSet都是KeyframeSet的子類.

private PropertyValuesHolder(String propertyName) {
	mPropertyName = propertyName;
}
public void setFloatValues(float... values) {
	mValueType = float.class;
	mKeyframes = KeyframeSet.ofFloat(values);
}

KeyframeSet會更具傳入的參數個數執行不同的流程,如果只是參數一個值那麼這個值就作爲最後一幀.如果傳入了多個參數,也會根據參數的個數來設置.

public static KeyframeSet ofFloat(float... values) {
	boolean badValue = false;
	int numKeyframes = values.length;
	FloatKeyframe keyframes[] = new FloatKeyframe[Math.max(numKeyframes,2)];
	if (numKeyframes == 1) {
		keyframes[0] = (FloatKeyframe) Keyframe.ofFloat(0f);
		keyframes[1] = (FloatKeyframe) Keyframe.ofFloat(1f, values[0]);
		if (Float.isNaN(values[0])) {
			badValue = true;
		}
	} else {
		keyframes[0] = (FloatKeyframe) Keyframe.ofFloat(0f, values[0]);
		for (int i = 1; i < numKeyframes; ++i) {
			keyframes[i] =
					(FloatKeyframe) Keyframe.ofFloat((float) i / (numKeyframes - 1), values[i]);
			if (Float.isNaN(values[i])) {
				badValue = true;
			}
		}
	}
	if (badValue) {
		Log.w("Animator", "Bad value (NaN) in float animator");
	}
	return new FloatKeyframeSet(keyframes);
}

上面代碼中的第15行的Keyframe.ofFloat()會返回一個FloatKeyframe,並作爲數組keyframes[]其中的一個值,最好把這個數組用來傳遞給FloatKeyframeSet的構造函數.

到了這裏我們還是回到前面繼續分析上面的實例的下一行代碼.

實例中的代碼調用先調用ofPropertyValuesHolder()再調用start().那我們就看看ofPropertyValuesHolder().

public static ObjectAnimator ofPropertyValuesHolder(Object target,
		PropertyValuesHolder... values) {
	ObjectAnimator anim = new ObjectAnimator();
	anim.setTarget(target);
	anim.setValues(values);
	return anim;
}

public void setValues(PropertyValuesHolder... values) {
	int numValues = values.length;
	mValues = values;
	mValuesMap = new HashMap<String, PropertyValuesHolder>(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;
}

ofPropertyValuesHolder()裏面創建了一個ObjectAnimator,target參數的中的視圖View,參數中的...values就是實例中的幾個ValuePropertyHolder對象.ObjectAnimator會使用setValues()將這些ValuePropertyHolder對象保存到一個HashMap中.

接下來就是要看看start()方法了.

ObjectAnimator的start()中前面部分在我們討論的實例中是不會執行,這裏我們分析一般的情況就可以了.所以就不關注前面部分,只看後面一行就可以了,其實ObjectAnimator的start()主要是調用它父類ValueAnimator來完成.

@Override
public void start() {
	start(false);
}
private void start(boolean playBackwards) {//當前情況是false
	if (Looper.myLooper() == null) {
		throw new AndroidRuntimeException("Animators may only be run on Looper threads");
	}
	mReversing = playBackwards;
	mPlayingBackwards = playBackwards;//false
	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();
}

ValueAnimator的無參數的start()方法就直接調用帶參數的start(boolean)方法,傳入的參數也是false.

在上面帶參數的start(boolean)方法中,

12到23行我們不需要關注,因爲if判斷不能pass,

24到33行我們暫時也不用關注,因爲我們當前實例沒有設置重複執行相關的狀態,上面實例2會執行這些代碼,我們這裏爲了流程簡單明瞭就不考慮這些.

34到38行主要是設置一些狀態值.其中pervPlayingState的默認值是STOPPED,

39行處理動畫時間長度相關,我們的實例目前並沒有執行setDurationScale,也不用擔心這些.

42行的if會pass,因爲我們沒有設置延遲,44的if也會pass,前面已經說了這個pervPlayingState默認是STOPPED.

49行是將設置的相關監聽動畫開始執行的AnimatorListener相關回調函數onAnimationStart執行起來.

所以剩下的重點就是在45行的setCurrentPlayTime(0)和最後一個的animationHandler.start();

先開始分析setCurrentPlayTime(0)的執行.

public void setCurrentPlayTime(long playTime) {
	float fraction = mUnscaledDuration > 0 ? (float) playTime / mUnscaledDuration : 1;
	setCurrentFraction(fraction);
}
public void setCurrentFraction(float fraction) {
	initAnimation();
	if (fraction < 0) {
		fraction = 0;
	}
	int iteration = (int) fraction;
	if (fraction == 1) {
		iteration -= 1;
	} else if (fraction > 1) {
		if (iteration < (mRepeatCount + 1) || mRepeatCount == INFINITE) {
			if (mRepeatMode == REVERSE) {
				mPlayingBackwards = (iteration % 2) != 0;
			}
			fraction = fraction % 1f;
		} else {
			fraction = 1;
			iteration -= 1;
		}
	} else {
		mPlayingBackwards = mReversing;
	}
	mCurrentIteration = iteration;
	long seekTime = (long) (mDuration * fraction);
	long currentTime = AnimationUtils.currentAnimationTimeMillis();
	mStartTime = currentTime - seekTime;
	if (mPlayingState != RUNNING) {
		mSeekFraction = fraction;
		mPlayingState = SEEKED;
	}
	if (mPlayingBackwards) {
		fraction = 1f - fraction;
	}
	animateValue(fraction);//調用子類ObjectAnimator重寫的方法
}

由於setCurrentPlayTime的參數爲0,而我們前面已經提到過動畫的時長不是0,所以setCurrentFraction()的參數也會是0.這裏我們直接看setCurrentFraction()的最後一行.但是這裏需要注意是這裏是執行的ValueAnimator的子類ObjectAnimator的animateValue().

ObjectAnimator.java

@Override
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);
	}
}

主要上面代碼的13行並不是執行的ValuePropertyHolder的setAnimateValue方法,而且其對於的子類FloatProperyHolder的方法.

ValueAnimator.java

這裏主要是執行監聽動畫執行中屬性改變的回調函數onAnimationUpdate.上面的實例1可以參考.

其中下面代碼的第6行是根據當前參數fraction來計算當前幀的值.

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);
		}
	}
}

FloatPropertyHolder.java

@Override
void setAnimatedValue(Object target) {
	if (mFloatProperty != null) {
		mFloatProperty.setValue(target, mFloatAnimatedValue);
		return;
	}
	if (mProperty != null) {
		mProperty.set(target, mFloatAnimatedValue);
		return;
	}
	if (mJniSetter != 0) {
		nCallFloatMethod(target, mJniSetter, mFloatAnimatedValue);
		return;
	}
	if (mSetter != null) {
		try {
			mTmpValueArray[0] = mFloatAnimatedValue;
			mSetter.invoke(target, mTmpValueArray);
		} catch (InvocationTargetException e) {
			Log.e("PropertyValuesHolder", e.toString());
		} catch (IllegalAccessException e) {
			Log.e("PropertyValuesHolder", e.toString());
		}
	}
}

在我們當前的實例中,第5和9行並不會執行,因爲我們在實例是直接使用String類型的屬性,並沒有去封裝.那麼關鍵就是滴13行和17行的if判斷了,

根據實際添加的log來看,第17行的mSetter會是null.第13行的mJniSetter不等於null.也就是是最終會調用本地函數nCallFloatMethod.也就是說試了JNI了.其實我很疑惑,有些屬性在對應的View對象裏面明明有對應的get和set方法,爲什麼mSetter還是null.還要去執行JNI.疑惑啊,暫時沒有搞明白,後續有時間再分析記錄.

接着回到前面分析,我們要開始ValueAnimator的start(boolean)的最後一行

private void start(boolean playBackwards) {//當前情況是false
	//....
	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();
}

這裏的AnimationHandler其實是一個實現了Runnable接口的類,並不是一個Handler.它的start()會調用scheduleAnimation().最後會執行Runnable的run()方法.run()方法又會轉調scheduleAnimation(),從而實現動畫效果的逐步實現.這個過程比較複雜,暫時不做分析.

筆記待完善點

1. 上面FloatPropertyHolder中的爲什麼是執行的JNI不是直接執行對應視圖的set方法.

2.AnimationHandler 的start()流程

鏈接:

http://www.netfoucs.com/article/x359981514/92198.html#

http://blog.csdn.net/lmj623565791/article/details/42056859