ViewTreeObserver

API文档链接

Structure

public final class
ViewTreeObserver
extends Object
java.lang.Object
↳ android.view.ViewTreeObserver
继承Object

Class Overview

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 getViewTreeObserver() for more information.
此为监听本视图树是否有变化的观察者，这些变化包括整个树的布局，开始绘图，触摸方式发生改变….等等，此观察者不能实例化。

Summery

• Interface

  ViewTreeObserver.OnDrawListener 监听视图树将被绘图ViewTreeObserver.OnPreDrawListener 同上ViewTreeObserver.OnGlobalFocusChangeListener 监听焦点ViewTreeObserver.OnGlobalLayoutListener 状态、可见性ViewTreeObserver.OnScrollChangedListener 滚动ViewTreeObserver.OnTouchModeChangeListener 触摸模式ViewTreeObserver.OnWindowAttachListener 从win添加or者分离视图结构

• Method
  public void
  addOnDrawListener(ViewTreeObserver.OnDrawListener listener)
  removeOnDrawListener(ViewTreeObserver.OnDrawListener victim)
  …………
  查看具体API文档

  Example:view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {@Overridepublic void onGlobalLayout() { //do something //视图会一直重绘，故要及时撤销监听  if (Build.VERSION.SDK_INT >=       Build.VERSION_CODES.JELLY_BEAN) {                    view.getViewTreeObserver().removeOnGlobalLayoutListener(this);} else {                    view.getViewTreeObserver().removeGlobalOnLayoutListener(this);  }}});