3. Property Animation

属性动画，这个是在Android 3.0中才引进的，它更改的是对象的实际属性，在View Animation（Tween Animation）中，其改变的是View的绘制效果，真正的View的属性保持不变，比如无论你在对话中如何缩放Button的大小，Button的有效点击区域还是没有应用动画时的区域，其位置与大小都不变。而在Property Animation中，改变的是对象的实际属性，如Button的缩放，Button的位置与大小属性值都改变了。而且Property Animation不止可以应用于View，还可以应用于任何对象。Property Animation只是表示一个值在一段时间内的改变，当值改变时要做什么事情完全是你自己决定的。

在Property Animation中，可以对动画应用以下属性：

• Duration：动画的持续时间
• TimeInterpolation：属性值的计算方式，如先快后慢
• TypeEvaluator：根据属性的开始、结束值与TimeInterpolation计算出的因子计算出当前时间的属性值
• Repeat Count and behavoir：重复次数与方式，如播放3次、5次、无限循环，可以此动画一直重复，或播放完时再反向播放
• Animation sets：动画集合，即可以同时对一个对象应用几个动画，这些动画可以同时播放也可以对不同动画设置不同开始偏移
• Frame refreash delay：多少时间刷新一次，即每隔多少时间计算一次属性值，默认为10ms，最终刷新时间还受系统进程调度与硬件的影响

  
  

  Interpolator

  
  

  首先要了解为什么需要插值器，因为在补间动画中，我们一般只定义关键帧（首帧或尾帧），然后由系统自动生成中间帧，生成中间帧的这个过程可以成为“插值”。插值器定义了动画变化的速率，提供不同的函数定义变化值相对于时间的变化规则，可以定义各种各样的非线性变化函数，比如加速、减速等。下面是几种常见的插值器：

  Interpolator对象	资源ID	功能作用
  AccelerateDecelerateInterpolator	@android:anim/accelerate_decelerate_interpolator	先加速再减速
  AccelerateInterpolator	@android:anim/accelerate_interpolator	加速
  AnticipateInterpolator	@android:anim/anticipate_interpolator	先回退一小步然后加速前进
  AnticipateOvershootInterpolator	@android:anim/anticipate_overshoot_interpolator	在上一个基础上超出终点一小步再回到终点
  BounceInterpolator	@android:anim/bounce_interpolator	最后阶段弹球效果
  CycleInterpolator	@android:anim/cycle_interpolator	周期运动
  DecelerateInterpolator	@android:anim/decelerate_interpolator	减速
  LinearInterpolator	@android:anim/linear_interpolator	匀速
  OvershootInterpolator	@android:anim/overshoot_interpolator	快速到达终点并超出一小步最后回到终点

  
  

  如果只简单地引用这些插值器还不能满足需要的话，我们要考虑一下个性化插值器。我们可以创建一个插值器资源修改插值器的属性，比如修改AnticipateInterpolator的加速速率，调整CycleInterpolator的循环次数等。为了完成这种需求，我们需要创建XML资源文件，然后将其放于/res/anim下，然后再动画元素中引用即可。我们先来看一下几种常见的插值器可调整的属性：

  ?
•   android:tension 浮点值，起始点后退的张力、拉力数，默认为2  android:tension 同上 android:extraTension 浮点值，拉力的倍数，默认为1.5（2 * 1.5） 无 android:cycles 整数值，循环的个数，默认为1 android:factor 浮点值，减速的速率，默认为1 无 浮点值，超出终点后的张力、拉力，默认为2
  
• 
  
  

  下面我们就拿最后一个插值器来举例：

  ?

  1 2	"http://schemas.android.com/apk/res/android" android:tension= "7.0" >

  上面的代码中，我们把张力改为7.0，然后将此文件命名为my_overshoot_interpolator.xml，放置于/res/anim下，我们就可以引用到自定义的插值器了： 
  ?

  1	"http://schemas.android.com/apk/res/android" android:interpolator= "@anim/my_overshoot_interpolator" ...= "" >

  
  

  AccelerateDecelerateInterpolator

  ?

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

  /**   * An interpolator where the rate of change starts and ends slowly but   * accelerates through the middle.   *   */ public class AccelerateDecelerateInterpolator implements Interpolator {      public AccelerateDecelerateInterpolator() {      }            @SuppressWarnings ({ "UnusedDeclaration" })      public AccelerateDecelerateInterpolator(Context context, AttributeSet attrs) {      }            public float getInterpolation( float input) {          return ( float )(Math.cos((input + 1 ) * Math.PI) / 2 .0f) + 0 .5f;      } }

  
  
  

  

  <喎�"/kf/ware/vc/" target="_blank" class="keylink">vcD4KPGgyPgpBY2NlbGVyYXRlSW50ZXJwb2xhdG9yPC9oMj4KPHByZSBjbGFzcz0="brush:java;">/** * An interpolator where the rate of change starts out slowly and * and then accelerates. * */ public class AccelerateInterpolator implements Interpolator { private final float mFactor; private final double mDoubleFactor; public AccelerateInterpolator() { mFactor = 1.0f; mDoubleFactor = 2.0; } /** * Constructor * * @param factor Degree to which the animation should be eased. Seting * factor to 1.0f produces a y=x^2 parabola. Increasing factor above * 1.0f exaggerates the ease-in effect (i.e., it starts even * slower and ends evens faster) */ public AccelerateInterpolator(float factor) { mFactor = factor; mDoubleFactor = 2 * mFactor; } public AccelerateInterpolator(Context context, AttributeSet attrs) { TypedArray a = context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.AccelerateInterpolator); mFactor = a.getFloat(com.android.internal.R.styleable.AccelerateInterpolator_factor, 1.0f); mDoubleFactor = 2 * mFactor; a.recycle(); } public float getInterpolation(float input) { if (mFactor == 1.0f) { return input * input; } else { return (float)Math.pow(input, mDoubleFactor); } } }
  
  

  

  AnticipateInterpolator

  ?

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

  /**   * An interpolator where the change starts backward then flings forward.   */ public class AnticipateInterpolator implements Interpolator {      private final float mTension;        public AnticipateInterpolator() {          mTension = 2 .0f;      }        /**       * @param tension Amount of anticipation. When tension equals 0.0f, there is       *                no anticipation and the interpolator becomes a simple       *                acceleration interpolator.       */      public AnticipateInterpolator( float tension) {          mTension = tension;      }        public AnticipateInterpolator(Context context, AttributeSet attrs) {          TypedArray a = context.obtainStyledAttributes(attrs,                  com.android.internal.R.styleable.AnticipateInterpolator);            mTension =                  a.getFloat(com.android.internal.R.styleable.AnticipateInterpolator_tension, 2 .0f);            a.recycle();      }        public float getInterpolation( float t) {          // a(t) = t * t * ((tension + 1) * t - tension)          return t * t * ((mTension + 1 ) * t - mTension);      } }

  
  
  

  

  AnticipateOvershootInterpolator

  ?

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

  /**   * An interpolator where the change starts backward then flings forward and overshoots   * the target value and finally goes back to the final value.   */ public class AnticipateOvershootInterpolator implements Interpolator {      private final float mTension;        public AnticipateOvershootInterpolator() {          mTension = 2 .0f * 1 .5f;      }        /**       * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,       *                there is no anticipation/overshoot and the interpolator becomes       *                a simple acceleration/deceleration interpolator.       */      public AnticipateOvershootInterpolator( float tension) {          mTension = tension * 1 .5f;      }        /**       * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,       *                there is no anticipation/overshoot and the interpolator becomes       *                a simple acceleration/deceleration interpolator.       * @param extraTension Amount by which to multiply the tension. For instance,       *                     to get the same overshoot as an OvershootInterpolator with       *                     a tension of 2.0f, you would use an extraTension of 1.5f.       */      public AnticipateOvershootInterpolator( float tension, float extraTension) {          mTension = tension * extraTension;      }        public AnticipateOvershootInterpolator(Context context, AttributeSet attrs) {          TypedArray a = context.obtainStyledAttributes(attrs, AnticipateOvershootInterpolator);            mTension = a.getFloat(AnticipateOvershootInterpolator_tension, 2 .0f) *                  a.getFloat(AnticipateOvershootInterpolator_extraTension, 1 .5f);            a.recycle();      }        private static float a( float t, float s) {          return t * t * ((s + 1 ) * t - s);      }        private static float o( float t, float s) {          return t * t * ((s + 1 ) * t + s);      }        public float getInterpolation( float t) {          // a(t, s) = t * t * ((s + 1) * t - s)          // o(t, s) = t * t * ((s + 1) * t + s)          // f(t) = 0.5 * a(t * 2, tension * extraTension), when t < 0.5          // f(t) = 0.5 * (o(t * 2 - 2, tension * extraTension) + 2), when t <= 1.0          if (t < 0 .5f) return 0 .5f * a(t * 2 .0f, mTension);          else return 0 .5f * (o(t * 2 .0f - 2 .0f, mTension) + 2 .0f);      } }

  
  
  

  

  BounceInterpolator

  ?

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

  /**   * An interpolator where the change bounces at the end.   */ public class BounceInterpolator implements Interpolator {      public BounceInterpolator() {      }        @SuppressWarnings ({ "UnusedDeclaration" })      public BounceInterpolator(Context context, AttributeSet attrs) {      }        private static float bounce( float t) {          return t * t * 8 .0f;      }        public float getInterpolation( float t) {          // _b(t) = t * t * 8          // bs(t) = _b(t) for t < 0.3535          // bs(t) = _b(t - 0.54719) + 0.7 for t < 0.7408          // bs(t) = _b(t - 0.8526) + 0.9 for t < 0.9644          // bs(t) = _b(t - 1.0435) + 0.95 for t <= 1.0          // b(t) = bs(t * 1.1226)          t *= 1 .1226f;          if (t < 0 .3535f) return bounce(t);          else if (t < 0 .7408f) return bounce(t - 0 .54719f) + 0 .7f;          else if (t < 0 .9644f) return bounce(t - 0 .8526f) + 0 .9f;          else return bounce(t - 1 .0435f) + 0 .95f;      } }

  
  
  

  

  CycleInterpolator

  ?

  1 2 3 4 5 6 7 8 9 10 11