protected void onDetachedFromWindow()方法的应用

protected void onAttachedToWindow()

 This is called when the view is attached to a window. At this point it has a Surface and will    start drawing. Note that this function is guaranteed to be called  before 

onDraw(android.graphics.Canvas)

,however it may be called any time before the first  onDraw -- including before or after 

onMeasure(int,
int)

.如果你在自己的view中Override了这个方法。那么我们最关注的是它什么时候调用？从开发文档中我们可以看出，onAttachedToWindow是在第一次onDraw前调用的。也就是我们写的View在没有绘制出来时调用的，但只会调用一次。比如，我们写状态栏中的时钟的View，在onAttachedToWindow这方法中做初始化工作，比如注册一些广播等等……  与onAttachedToWindow 相反的则是这个方法： 

protected void onDetachedFromWindow()

Since: API Level 1This is called when the view is detached from a window. At this point it no longer has a surface for drawing.

开发文档就简单的两句。也就是我们销毁View的时候。我们写的这个View不再显示。

这时我们就在这个方法做一些收尾工作，如：取消广播注册等等。

究竟是如何的调用顺序，我在播放界面的Activity中重写了这2个方法，并在其中打印Log,下面我们来看一下运行效果。A：表示刚进入视频播放页面时执行的一系列。B：表示点击back键退出视频播放页面时执行的一些列操作上面一个椭圆部分，表示播放视频的初始化操作。下面一个椭圆部分，表示播放视频的销毁操作，比如释放资源。由此可见，onAttachedToWindow在初始化视频播放（既创建view）之前调用，onDetachedFromWindow在退出视频播放，销毁资源（既销毁view）之后调用。在 Adroid2.1 和 Adroid2.2 设备上，如果 Activity 中使用到 ViewFlipper 控件，进行横竖屏切换操作时会发生如下错误信息:

1 Program crashes, giving this crash log:23 java.lang.IllegalArgumentException: Receiver not registered: android.widget.ViewFlipper$1@44b6ab904     at android.app.ActivityThread$PackageInfo.forgetReceiverDispatcher(ActivityThread.java:667)5     at android.app.ApplicationContext.unregisterReceiver(ApplicationContext.java:747)6     at android.content.ContextWrapper.unregisterReceiver(ContextWrapper.java:321)7     at android.widget.ViewFlipper.onDetachedFromWindow(ViewFlipper.java:104)8     at android.view.View.dispatchDetachedFromWindow(View.java:5835)9     at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:1076)10     at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:1074)11     at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:1074)12     at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:1074)13     at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:1074)14     at android.view.ViewRoot.dispatchDetachedFromWindow(ViewRoot.java:1570)15     at android.view.ViewRoot.doDie(ViewRoot.java:2556)16     at android.view.ViewRoot.die(ViewRoot.java:2526)17     at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:218)18     at android.view.Window$LocalWindowManager.removeViewImmediate(Window.java:436)19     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3498)20     at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3599)21     at android.app.ActivityThread.access$2300(ActivityThread.java:119)22     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1867)23     at android.os.Handler.dispatchMessage(Handler.java:99)24     at android.os.Looper.loop(Looper.java:123)25     at android.app.ActivityThread.main(ActivityThread.java:4363)26     at java.lang.reflect.Method.invokeNative(Native Method)27     at java.lang.reflect.Method.invoke(Method.java:521)28     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)29     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)30     at dalvik.system.NativeStart.main(Native Method)

这是由于 onDetachedFromWindow() 莫名其妙地在 onAttachedToWindow() 之前被调用了。先提供解决方案如下：1.重载ViewFlipper的onDetachedFromWindow()方法，注意修改访问修饰符为public。 @Overridepublic void onDetachedFromWindow(){      //因为该问题多发生于2.1或者2.2设备上，所以做此判断，如果其他API Level也出现类似情况，只要修       //改这个地方即可。 if (Build.VERSION.SDK_INT == 7) { try {super.onDetachedFromWindow();} catch (IllegalArgumentException e) {Log.w(TAG, "Android project  issue 6191  workaround.");e.printStackTrace();} finally {super.stopFlipping();}} else {super.onDetachedFromWindow();}}若第一步不起作用，则在第一步的基础上，紧接着进行第二步：2. 重载Activity的onDetachedFromWindow()在其中加入@Overridepublic void onDetachedFromWindow() {if (myFlipper != null) {myFlipper.onDetachedFromWindow();// 第一步中修饰符修改为了public，这里才能访问到。}}当然进行第二步的前提是，你已经重载了ViewFlipper的onDetachdFromWindow()方法,既第一步。