Android ViewTreeObserver的常用技巧

A view tree observer is used to register listeners that can be notified of global changes in the view tree. Such global events include, but are not limited to, layout of the whole tree, beginning of the drawing pass, touch mode change…. A ViewTreeObserver should never be instantiated by applications as it is provided by the views hierarchy. Refer to View.getViewTreeObserver() for more information.

从上面的描述中，不难看出，ViewTreeObserver是用来帮助我们监听某些View的某些变化的。

在 ViewTreeObserver 中，包含了以下几个接口：

interface ViewTreeObserver.OnGlobalFocusChangeListener

interface ViewTreeObserver.OnGlobalLayoutListener

interface ViewTreeObserver.OnPreDrawListener

interface ViewTreeObserver.OnScrollChangedListener

interface ViewTreeObserver.OnTouchModeChangeListener

本文将测试除 ViewTreeObserver.OnScrollChangedListener 外的四个接口

创建一个 Android Project ，修改 main.xml 使之如下：