App->Activity->Animation 示例用于演示不同Activity切换时动态效果。例子中定义了两种动画效果，渐变Fade In, 新出现的Activity由浅入深逐渐显示，放大效果Zoom ，新出现的Activity由小及大逐渐显示。
Android 中 Animation 资源可以分为两种：
Tween Animation 对单个图像进行各种变换（缩放，平移，旋转等）来实现动画。
Frame Animation 由一组图像顺序显示显示动画。
Animation 中使用的是Tween Animation， 使用的资源为R.anim.fade, R.anim.hold，R.anim.zoom_enter, R.anim.zoom_exit。
其中R.anim.fade， R.anim.zoom_enter分别为Fade In 和 Zoom动画资源。其定义为
fade.xml
[html]
<alpha xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@android:anim/accelerate_interpolator”
android:fromAlpha=”0.0″ android:toAlpha=”1.0″
android:duration=”@android:integer/config_longAnimTime” />
<alpha xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@android:anim/accelerate_interpolator”
android:fromAlpha=”0.0″ android:toAlpha=”1.0″
android:duration=”@android:integer/config_longAnimTime” />
zoom_center.xml
[html]
<set xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@android:anim/decelerate_interpolator”>
<scale android:fromXScale=”2.0″ android:toXScale=”1.0″
android:fromYScale=”2.0″ android:toYScale=”1.0″
android:pivotX=”50%p” android:pivotY=”50%p”
android:duration=”@android:integer/config_mediumAnimTime” />
</set>
<set xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@android:anim/decelerate_interpolator”>
<scale android:fromXScale=”2.0″ android:toXScale=”1.0″
android:fromYScale=”2.0″ android:toYScale=”1.0″
android:pivotX=”50%p” android:pivotY=”50%p”
android:duration=”@android:integer/config_mediumAnimTime” />
</set>
tween animation 资源定义的格式如下：
[html]
<?xml version=”1.0″ encoding=”utf-8″?>
<set xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@[package:]anim/interpolator_resource”
android:shareInterpolator=[ ” true ” false “>
<alpha
android:fromAlpha=”float”
android:toAlpha=”float” />
<scale
android:fromXScale=”float”
android:toXScale=”float”
android:fromYScale=”float”
android:toYScale=”float”
android:pivotX=”float”
android:pivotY=”float” />
<translate
android:fromXDelta=”float”
android:toXDelta=”float”
android:fromYDelta=”float”
android:toYDelta=”float” />
<rotate
android:fromDegrees=”float”
android:toDegrees=”float”
android:pivotX=”float”
android:pivotY=”float” />
<set> …
</set>
</set>
<?xml version=”1.0″ encoding=”utf-8″?>
<set xmlns:android=”http://schemas.android.com/apk/res/android”
android:interpolator=”@[package:]anim/interpolator_resource”
android:shareInterpolator=[ ” true ” false “>
<alpha
android:fromAlpha=”float”
android:toAlpha=”float” />
<scale
android:fromXScale=”float”
android:toXScale=”float”
android:fromYScale=”float”
android:toYScale=”float”
android:pivotX=”float”
android:pivotY=”float” />
<translate
android:fromXDelta=”float”
android:toXDelta=”float”
android:fromYDelta=”float”
android:toYDelta=”float” />
<rotate
android:fromDegrees=”float”
android:toDegrees=”float”
android:pivotX=”float”
android:pivotY=”float” />
<set> …
</set>
</set>
<set> 为其它animation类型<alpha>,<scale>,<translate>和<rotate>或其它<set>的容器。
android:interpolator 为Interpolator资源ID，Interpolator定义了动画的变化速率，动画的各帧的显示可以加速，减速，重复显示。
android:shareInterpolator 如果想为<set>中的各个子动画定义共享interpolator，shareInterpolator 则设为true.
<alpha> 定义Fade in ,Fade out 动画，其对应的Android类AlphaAnimation，参数由fromAlpha,toAlpha定义。
<scale>定义缩放动画，其对应的Android类为ScaleAnimation，参数由fromXScale,toXScale,fromYScale,toYScale,pivotX,pivotY定义，pivotX,pivotY定义了缩放时的中心。
<translate>定义平移动画，其对应的Android类为TranslateAnimation，参数由fromXDelta,toXDelta,fromYDelta,toYDelta定义。
<rotate>定义选择动画，其对应的Android类RotateAnimation，参数由fromDegrees,toDegrees,pivotX,pivotY， pivotX,pivotY定义选择中心。
Animation中的Fade In和Zoom In按钮的事件处理代码：
[java]
private OnClickListener mFadeListener = new OnClickListener() {
public void onClick(View v) {
// Request the next activity transition (here starting a new one).
startActivity(new Intent(Animation.this, Controls1.class));
// Supply a custom animation.This one will just fade the new
// activity on top.Note that we need to also supply an animation
// (here just doing nothing for the same amount of time) for the
// old activity to prevent it from going away too soon.
overridePendingTransition(R.anim.fade, R.anim.hold);
}
};</p>
<p>private OnClickListener mZoomListener = new OnClickListener() {
public void onClick(View v) {
// Request the next activity transition (here starting a new one).
startActivity(new Intent(Animation.this, Controls1.class));
// This is a more complicated animation, involving transformations
// on both this (exit) and the new (enter) activity.Note how for
// the duration of the animation we force the exiting activity
// to be Z-ordered on top (even though it really isn't) to achieve
// the effect we want.
overridePendingTransition(R.anim.zoom_enter, R.anim.zoom_exit);
}
};
private OnClickListener mFadeListener = new OnClickListener() {
public void onClick(View v) {
// Request the next activity transition (here starting a new one).
startActivity(new Intent(Animation.this, Controls1.class));
// Supply a custom animation.This one will just fade the new
// activity on top.Note that we need to also supply an animation
// (here just doing nothing for the same amount of time) for the
// old activity to prevent it from going away too soon.
overridePendingTransition(R.anim.fade, R.anim.hold);
}
};</p>
<p>private OnClickListener mZoomListener = new OnClickListener() {
public void onClick(View v) {
// Request the next activity transition (here starting a new one).
startActivity(new Intent(Animation.this, Controls1.class));
// This is a more complicated animation, involving transformations
// on both this (exit) and the new (enter) activity.Note how for
// the duration of the animation we force the exiting activity
// to be Z-ordered on top (even though it really isn't) to achieve
// the effect we want.
overridePendingTransition(R.anim.zoom_enter, R.anim.zoom_exit);
}
};
从代码可以看到Activity Animation到其它Activity Controls1 切换的动画使用overridePendingTransition 来定义，函数overridePendingTransition(int enterAnim, int exitAnim) 必须定义在StartActivity（Intent）或是 Activity.finish()之后来定义两个Activity切换时的动画，enterAnim 为新Activity出现时动画效果，exitAnim则定义了当前Activity退出时动画效果
作者：mapdigit
