Android PropertyAnimation官网文档翻译

点击打开官方Animation文档

简述：

能不用PropertyAnimation就不用，如果只是做View就用ViewPropertyAnimator多个属性一起改。ViewAnimation并没有改变View的属性，点击还是原来区域。

Property Animation 和 View Animation

ViewAnimation有很强的局限性：只能操作View对象、View的部分属性（不包含背景色）、只是改变View在哪里绘制，没有改变相应逻辑（比如Button移动，你点击的地方仍旧是以前的，相应逻辑需要你自己写）。

因为ViewAnimation改变View的绘制，所以是通过操控他的父View，ViewGroup来完成的，因为View本身没有这样的属性。所以View对象本身没有变化，导致View的行为操作，仍旧停留在原来区域。3.0后添加了get、set方法，就行bug修复。

而PropertyAnimation可以View对象的真实属性（调用方法），所以View会自动调用invalidate方法（View set方法会调）

然而ViewAnimation体系启动时间更少、需要代码更少。所以了ViewAnimation够用了，就别用PropertyAnimation。

PropertyAnimation API:

ValueAnimator：

就是指定数值区间、时间，然后在监听器中做你想做的事情（如动画）。（也就是改什么属性是你在回调中写的，实际上你只控制了速度），Animation有两个阶段：算数值、设置对象的属性值。  ValueAnimator只负责第一个阶段，第二个阶段程序员自己写。

获取数值的API是getAnimatedValue()

ValueAnimator animation = ValueAnimator.ofFloat(0f, 1f);
animation.setDuration(1000);
animation.start();

ValueAnimator animation = ValueAnimator.ofObject(new MyTypeEvaluator(), startPropertyValue, endPropertyValue);
animation.setDuration(1000);
animation.start();

ObjectAnimator：

上述的两个阶段都负责，所以要指定属性名称。类需要提供set和get方法，方法的命名方式要符合驼峰命名。如alpha属性，要有个setAlpha，getAlpha防范。如果三个次，如helloWorld，那set方法就是setHelloWorld

ObjectAnimator anim = ObjectAnimator.ofFloat(foo, "alpha", 0f, 1f);
anim.setDuration(1000);
anim.start();

根据不同的属性值，你可能需要调用invalidate方法，在onAnimationUpdate() 这个回调中调用。例如Drawable对象的color属性，就只有你主动调用才刷新。而View类的所有带set***方法的属性***都会自己主动刷新，就不用你再调用了。

AnimatorSet:

就是让多个Animator，按照某种顺序发生（同时了、一个结束了、一个开始了）。

AnimatorSet bouncer = new AnimatorSet();
bouncer.play(bounceAnim).before(squashAnim1);
bouncer.play(squashAnim1).with(squashAnim2);
bouncer.play(squashAnim1).with(stretchAnim1);
bouncer.play(squashAnim1).with(stretchAnim2);
bouncer.play(bounceBackAnim).after(stretchAnim2);
ValueAnimator fadeAnim = ObjectAnimator.ofFloat(newBall, "alpha", 1f, 0f);
fadeAnim.setDuration(250);
AnimatorSet animatorSet = new AnimatorSet();
animatorSet.play(bouncer).before(fadeAnim);
animatorSet.start();		

对ViewGroup布局的改变：

使用LayoutTransition

• APPEARING - A flag indicating the animation that runs on items that are appearing in the container.
• CHANGE_APPEARING - A flag indicating the animation that runs on items that are changing due to a new item appearing in the container.
• DISAPPEARING - A flag indicating the animation that runs on items that are disappearing from the container.
• CHANGE_DISAPPEARING - A flag indicating the animation that runs on items that are changing due to an item disappearing from the container.

使用Interpolator:

加速器提供时间和返回值之间的映射关系。自己写就继承TimeInterpolator，或者用android.view.animation包里的。

AccelerateDecelerateInterpolator

public float getInterpolation(float input) {
    return (float)(Math.cos((input + 1) * Math.PI) / 2.0f) + 0.5f;
}

监听器：实现接口Animator.AnimatorListener，或者有空方法让你重写的AnimatorListenerAdapter类。

使用自定义的TypeEvaluator：

public class FloatEvaluator implements TypeEvaluator {

    public Object evaluate(float fraction, Object startValue, Object endValue) {
        float startFloat = ((Number) startValue).floatValue();
        return startFloat + fraction * (((Number) endValue).floatValue() - startFloat);
    }
}

监听关键的帧：

Keyframe kf0 = Keyframe.ofFloat(0f, 0f);
Keyframe kf1 = Keyframe.ofFloat(.5f, 360f);
Keyframe kf2 = Keyframe.ofFloat(1f, 0f);
PropertyValuesHolder pvhRotation = PropertyValuesHolder.ofKeyframe("rotation", kf0, kf1, kf2);
ObjectAnimator rotationAnim = ObjectAnimator.ofPropertyValuesHolder(target, pvhRotation)
rotationAnim.setDuration(5000ms);

新增API中的属性：

• 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 (rotationproperty) 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).

例子

ViewPropertyAnimator：

对比：

Multiple ObjectAnimator objects

ObjectAnimator animX = ObjectAnimator.ofFloat(myView, "x", 50f);
ObjectAnimator animY = ObjectAnimator.ofFloat(myView, "y", 100f);
AnimatorSet animSetXY = new AnimatorSet();
animSetXY.playTogether(animX, animY);
animSetXY.start();

One ObjectAnimator

PropertyValuesHolder pvhX = PropertyValuesHolder.ofFloat("x", 50f);
PropertyValuesHolder pvhY = PropertyValuesHolder.ofFloat("y", 100f);
ObjectAnimator.ofPropertyValuesHolder(myView, pvhX, pvyY).start();

ViewPropertyAnimator

myView.animate().x(50f).y(100f);

使用XML：

为了区分ViewAnimation，需要在res/animator/目录取代res/anim/目录，要预览的话，系统只会在上述路径下扫描PropertyAnimation

• ValueAnimator - <animator>
• ObjectAnimator - <objectAnimator>
• AnimatorSet - <set>

<set android:ordering="sequentially">
    <set>
        <objectAnimator
            android:propertyName="x"
            android:duration="500"
            android:valueTo="400"
            android:valueType="intType"/>
        <objectAnimator
            android:propertyName="y"
            android:duration="500"
            android:valueTo="300"
            android:valueType="intType"/>
    </set>
    <objectAnimator
        android:propertyName="alpha"
        android:duration="500"
        android:valueTo="1f"/>
</set>

AnimatorSet set = (AnimatorSet) AnimatorInflater.loadAnimator(myContext,
    R.anim.property_animator);
set.setTarget(myObject);
set.start();