讲解anroid.view.animation。

android.view.animation

Provides classes that handle tweened animations.

Android provides two mechanisms that you can use to create simple animations: tweened animation, in which you tell Android to perform a series of simple transformations (position, size, rotation, and so on) to the content of a View; and frame-by-frame
animation, which loads a series of Drawable resources one after the other. Both animation types can be used in any View object to provide simple rotating timers, activity icons, and other useful UI elements. Tweened animation is handled by this package
(android.view.animation); frame-by-frame animation is handled by the AnimationDrawable class.

该类提供渐变动画。

Android提供了两种机制，你可以用它来创建简单的动画：渐变动画，在其中你告诉android执行一系列简单变换（位置，大小，旋转，等等）到视图的内容；逐帧动画，它加载一系列有序的Drawable资源。两种动画类型可以用在任何视图对象提供简单的旋转定时器，activity的图标，和其他有用的用户界面元素。渐变动画是由这个包处理（android.view.animation）；逐帧动画是由AnimationDrawable类处理。

Interfaces

Android Animation详解一