事件分为按键事件分发，触摸事件分发，还有轨迹球事件，轨迹球已经被淘汰，按键事件分发主要是在TV上，使用遥控器做按键操作。触摸事件分发及pointerEvent则是触摸屏设备的触摸点分发，此处主要讨论keyEvent事件分发。
分发过程：
第一步，WindowManagerService（WMS） 中有一个KeyInputQueue的子类,该类内部有一个thread去调用native方法读取用户的按键，触摸消息，然后把消息保存到QueueEvent的消息队列中，然后WMS中有一个对应的hander来处理这个输入消息队列InputDispatcherThread,它内部有一个线程对这些消息就行处理，然后分发给对应的窗口（至于怎么匹配对应的窗口这里不说）。
第二步：wms通过IPC的Binder机制把消息转给对应窗口PhoneWindow,它是actiivty的成员变量mWindow,PhoneWindow是一个window的子类，mWindow里面有一个成员变量mWindowManager，而mWindowManager是WindowMangerImpl类实例的引用，另外WindowMangerImpl里面包含ViewRoot,这个Viewroot就是Actvity与通信的一个handler对象，ViewRoot对应一个ViewRootImpl，其实现了一个InputHandler,ViewRoot拿到消息后调用InputHandler去调用handleKey函数，然后该函数再调用ViewRott的dispatchKey函数，会发送一个DISPATCH_KEY消息，然后调用deliverKeyEvent函数然后分三步走：
1.dispatchKeyEventPreIme （分发给输入法给一个机会去处理）
2.输入法去响应，如果输入法窗口处理了这个消息则直接返回，否则走第三步
3.deliverKeyEventPostIme(event, sendDone);
下面是这三步的源码：
1.privatevoiddeliverKeyEvent(KeyEvent event,booleansendDone) {
2.if(ViewDebug.DEBUG_LATENCY) {
3.mInputEventDeliverTimeNanos = System.nanoTime();
4.}
5.
6.if(mInputEventConsistencyVerifier !=null) {
7.mInputEventConsistencyVerifier.onKeyEvent(event,0);
8.}
9.
10.// If there is no view, then the event will not be handled.
11.if(mView ==null|| !mAdded) {
12.finishKeyEvent(event, sendDone,false);
13.return;
14.}
15.
16.if(LOCAL_LOGV) Log.v(TAG,"Dispatching key "+ event +" to "+ mView);
17.
18.// Perform predispatching before the IME.
19.if(mView.dispatchKeyEventPreIme(event)) {
20.finishKeyEvent(event, sendDone,true);
21.return;
22.}
23.
24.// Dispatch to the IME before propagating down the view hierarchy.
25.// The IME will eventually call back into handleFinishedEvent.
26.if(mLastWasImTarget) {
27.InputMethodManager imm = InputMethodManager.peekInstance();
28.if(imm !=null) {
29.intseq = enqueuePendingEvent(event, sendDone);
30.if(DEBUG_IMF) Log.v(TAG,"Sending key event to IME: seq="
31.+ seq +" event="+ event);
32.imm.dispatchKeyEvent(mView.getContext(), seq, event, mInputMethodCallback);
33.return;
34.}
35.}
36.
37.// Not dispatching to IME, continue with post IME actions.
38.deliverKeyEventPostIme(event, sendDone);
39.}
第三步：我们不考虑输入法窗口拦截key事件的操作，直接进入第三步deliverKeyEventPostIme,从里面进去有这么一段关键代码
1.if(mView.dispatchKeyEvent(event)) {
2.finishKeyEvent(event, sendDone,true);
3.return;
4.}
解析：mView是PhoneWindow.DecorView对象，DecorView是PhoneWindow的子类，继承于FramwLayout,其实这个DecorView就是我们看到的activity上对应的界面，它里面有一个title对应状态栏，还有一个contentview,对应activity里面的setContentView方法。DecorView是定义在PhoneWindow里面，我们看这个内部类的dispatchKeyEvent对应的源码：
public DecorView(Context context, int featureId) {
super(context);
mFeatureId = featureId;
}
public void setBackgroundFallback(int resId) {
mBackgroundFallback.setDrawable(resId != 0 ? getContext().getDrawable(resId) : null);
setWillNotDraw(getBackground() == null && !mBackgroundFallback.hasFallback());
}
@Override
public void onDraw(Canvas c) {
super.onDraw(c);
mBackgroundFallback.draw(mContentRoot, c, mContentParent);
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
final int keyCode = event.getKeyCode();
final int action = event.getAction();
final boolean isDown = action == KeyEvent.ACTION_DOWN;
if (isDown && (event.getRepeatCount() == 0)) {
// First handle chording of panel key: if a panel key is held
// but not released, try to execute a shortcut in it.
if ((mPanelChordingKey > 0) && (mPanelChordingKey != keyCode)) {
boolean handled = dispatchKeyShortcutEvent(event);
if (handled) {
return true;
}
}
// If a panel is open, perform a shortcut on it without the
// chorded panel key
if ((mPreparedPanel != null) && mPreparedPanel.isOpen) {
if (performPanelShortcut(mPreparedPanel, keyCode, event, 0)) {
return true;
}
}
}
//给activity一次处理dispatchKeyEvent的机会，比如按下菜单键，没消费的话最后还是调用getWindow.superDispatchKeyEvent回调了DecorView中super.dispatch方法中去了，也就是ViewGroup的dispatch方法
if (!isDestroyed()) {
final Callback cb = getCallback();
final boolean handled = cb != null && mFeatureId < 0 ? cb.dispatchKeyEvent(event);
super.dispatchKeyEvent(event);
if (handled) {
return true;
}
return isDown ? PhoneWindow.this.onKeyDown(mFeatureId, event.getKeyCode(), event)
: PhoneWindow.this.onKeyUp(mFeatureId, event.getKeyCode(), event);
}
}
源码注释的很清楚，首先处理系统快捷键，然后调用Window.callback的dispatchKeyEvent()(cb.dispatchKeyEvent(event),cb是一个window.callback的接口实现，这里就行接口回调，实现window.Callback的主要是activity),所以就走到了Activity里面的dispatchKeyEvent方法里面去了，下面我们看看Activity里面改方法做了啥：
public boolean dispatchKeyEvent(KeyEvent event) {
onUserInteraction();
// Let action bars open menus in response to the menu key prioritized over
// the window handling it
if (event.getKeyCode() == KeyEvent.KEYCODE_MENU &&
mActionBar != null && mActionBar.onMenuKeyEvent(event)) {
return true;
}
Window win = getWindow();
if (win.superDispatchKeyEvent(event)) {
return true;
}
View decor = mDecor;
if (decor == null) decor = win.getDecorView();
return event.dispatch(this, decor != null
? decor.getKeyDispatcherState() : null, this);
}
首先是win.superDispatchKeyEvent(event),PhoneWindow对应的源码是：
@Override
public boolean superDispatchKeyEvent(KeyEvent event) {
return mDecor.superDispatchKeyEvent(event);
}
这里还是调用的mDecor.superDispatchKeyEvent(event)对应于DecorView的源码是：
public boolean superDispatchKeyEvent(KeyEvent event) {
// Give priority to closing action modes if applicable.
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
final int action = event.getAction();
// Back cancels action modes first.
if (mActionMode != null) {
if (action == KeyEvent.ACTION_UP) {
mActionMode.finish();
}
return true;
}
}
return super.dispatchKeyEvent(event);
}
走到这里，我们发现它调用了super.dispatchKeyEvent(event)，也就是FrameLayout,我追踪到源码并无重写，故方法会走到ViewGroup的dispatchKeyEvent中去，这个是我们日常接触的最多的了。至于ViewGroup的DispatchKeyEvent如果走，我们后面再说。我们回到mView.dispatchKeyEvent中去，我们回忆一下步骤的三步：a.处理系统快捷键dispatchKeyShortcutEvent(event);b.a没有消费，则final cb.dispatchKeyEvent(event),此时进入actiivty的dispatchKeyevent中去处理，首先处理menu操作，如果没有消费，就调用phonwindow的superDispatchKeyEevent，最后走到的都是ViewGroup里面去递归, 如果我们看到的界面上的那些个view没有消费此事件，那么在在 return event.dispatch(this, decor != null
? decor.getKeyDispatcherState() : null, this);
这段代码是actiivty里面dispatchKeyEvent最后的返回，传的是actiivty自己的引用，跟踪之后发现调用的是KeyEvent的OnkeyDown事件，也就是activity里面的onkeyDown.
综上所述，activity里面的onkeydown是后于view里面的Onkeydown调用的。如果view里面的onkeydown消费了此事件，那么activity的onKeyDown是走不到的。
最后来整理一下思路，理一下流程：
1.ViewRoot里面的InputHandler的handleKey,然后再是ViewRoot的dispatchKey,然后再是deliverKeyEvent，如果View系统有输入法则被输入法窗口拦截InputMethodManager对象的dispatchKeyEvent。拦截之前有一次DecorView对象mView的dispatchKeyEventPreIme(event)的操作。然后如果没有拦截则RootViewImpl的deliverKeyEventPostIme方法。
源码对应于ViewRootImpl中：
1.privatevoiddeliverKeyEvent(QueuedInputEvent q) {
2.finalKeyEvent event = (KeyEvent)q.mEvent;s
3.if(mInputEventConsistencyVerifier !=null) {
4.mInputEventConsistencyVerifier.onKeyEvent(event,0);
5.}
6.
7.if((q.mFlags & QueuedInputEvent.FLAG_DELIVER_POST_IME) ==0) {
8.// If there is no view, then the event will not be handled.
9.if(mView ==null|| !mAdded) {
10.finishInputEvent(q,false);
11.return;
12.}
13.
14.if(LOCAL_LOGV) Log.v(TAG,"Dispatching key "+ event +" to "+ mView);
15.
16.// Perform predispatching before the IME.
17.if(mView.dispatchKeyEventPreIme(event)) {
18.finishInputEvent(q,true);
19.return;
20.}
21.
22.// Dispatch to the IME before propagating down the view hierarchy.
23.// The IME will eventually call back into handleImeFinishedEvent.
24.if(mLastWasImTarget) {
25.InputMethodManager imm = InputMethodManager.peekInstance();
26.if(imm !=null) {
27.finalintseq = event.getSequenceNumber();
28.if(DEBUG_IMF) Log.v(TAG,"Sending key event to IME: seq="
29.+ seq +" event="+ event);
30.imm.dispatchKeyEvent(mView.getContext(), seq, event, mInputMethodCallback);
31.return;
32.}
33.}
34.}
35.
36.// Not dispatching to IME, continue with post IME actions.
37.deliverKeyEventPostIme(q);
38.}
2.在ViewRootImpl的deliverKeyEventPostIme(q)方法中调用
1.// Deliver the key to the view hierarchy.
2.if(mView.dispatchKeyEvent(event)) {
3.finishInputEvent(q,true);
4.return;
5.}
3.mView就是DecorView对象的dispatchKeyEvent操作做了三步，一个是处理快捷键，二个是调用Window.Callback对象的dispatchKeyEvent。
最后如果上面两步都没消费就调用phonewindow的onKeyDown,onKeyUp事件。其中第二步是actiivty的dispatchKeyEvent为入口，里面是则会给增加了一个菜单按钮的拦截，然后就又调用Window对象的superDispatchKeyEvent方法，其实就是PhoneWindow的方法拦截，这个方法最后还是调用的mDecorView.superDispatchKeyEvent方法，这个方法拦截了back按键事件之后又把事件转给了DecorView的super.dispatchKeyEvent，最后走到了viewTree里面去了。