http://blog.csdn.net/elfylin/article/details/8008763

一. 接口
KeyEvent.Callback和View.OnKeyListener

二. 流程
a.Activity.dispatchKeyEvent
a.1.win.superDispatchKeyEvent(win=getWindow)
Window.superDispatchKeyEvent->PhoneWindow.superDispatchKeyEvent
a.2mDecor.superDispatchKeyEvent (mDecor=FrameLayout)
PhoneWindow.mDecor.superDispatchKeyEvent
a.3view. dispatchKeyEvent (Window.dispatchKeyEvent)
View.dispatchKeyEvent(View=mDecor)
b.event.dispatch
mOnKeyListener.onKey

三.Event
a. who call onKeyDown?
b. who call dispatchKeyevent
c. dispatchKeyEvent的实现在PhoneWindow.dispatchKeyEvent
PhoneWindows重载了View的dispatchKeyEvent和KeyEventCallback的OnKeyXX
首先调用dispatchKeyEvent,如果返回false才调用onKeyXX
在其父类View的dispatchKeyEvent，会调用KeyListener。

四.优先级
1.当一个Activity中收到事件，首先查看自己的decor是否有焦点，
1.1如果有调用它的dispatchKeyEvent，（即调用它的keylistener）；
1.2否则，获取焦点窗口，调用焦点窗口的dispatchKeyEvent；
2.如果上面都为false，就调用自己的onkeydown和onkeyup事件。

五 入口
HelloworldActivity.onKeyDown(int, KeyEvent) line: 25
KeyEvent.dispatch(KeyEvent$Callback, KeyEvent$DispatcherState, Object) line: 2555
HelloworldActivity(Activity).dispatchKeyEvent(KeyEvent) line: 2358
HelloworldActivity.dispatchKeyEvent(KeyEvent) line: 29
PhoneWindow$DecorView.dispatchKeyEvent(KeyEvent) line: 1806
ViewRootImpl.deliverKeyEventPostIme(KeyEvent, boolean) line: 3328
ViewRootImpl.handleFinishedEvent(int, boolean) line: 3301
ViewRootImpl.handleMessage(Message) line: 2461 
ViewRootImpl(Handler).dispatchMessage(Message) line: 99
Looper.loop() line: 137
ActivityThread.main(String[]) line: 4444
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 511
ZygoteInit$MethodAndArgsCaller.run() line: 787 
ZygoteInit.main(String[]) line: 554
NativeStart.main(String[]) line: not available [native method]