Android中按键消息的派发过程及源码分析
Android中消息的整体派发过程：接收消息——消息处理前端——窗口管理系统派发消息——窗口进行消息处理
以上过程中前三步都在WmS中完成，按键消息直接发送给当前窗口，而触摸消息则根据触摸坐标位置来匹配所有窗口，并判断坐标落到哪个窗口区域中，然后把消息发送给相应的窗口。对于按键消息还会涉及到“生理长按”的检测，比如一直按住某个键，那么会产生一些列的按键消息，然而第1个和第2个消息之间往往会间隔较长的时间，这种设计是人类本身的生理特点决定的，因为从按下到弹起的过程中，如果CPU处理太快，会导致产生多次该消息，这往往不是用户所期望的，因此Android把这种消息处理延迟加入到了消息处理前端中，应用程序不需要关心第一次的延迟，只需按普通的DOWN消息处理。
下面具体分析Android中按键消息的派发流程：
每个窗口定义了一个ViewRoot（4.0中是ViewRootImpl）对象，而ViewRoot对象中定义了一个inputHandler，窗口管理系统（WmS）派发消息的过程中会调用inputHandler的handlekey()，该函数再调用ViewRoot中的dispatchKey()函数
private final InputHandler mInputHandler = new InputHandler() {
public void handleKey(KeyEvent event, InputQueue.FinishedCallback finishedCallback) {
startInputEvent(finishedCallback);
dispatchKey(event, true);
}
public void handleMotion(MotionEvent event, InputQueue.FinishedCallback finishedCallback) {
startInputEvent(finishedCallback);
dispatchMotion(event, true);
}
};dispatchKey()函数内部发送一个DISPATCH_KEY消息，消息的处理函数为deliverKeyEvent():
private void dispatchKey(KeyEvent event, boolean sendDone) {
//noinspection ConstantConditions
if (false && event.getAction() == KeyEvent.ACTION_DOWN) {
if (event.getKeyCode() == KeyEvent.KEYCODE_CAMERA) {
if (DBG) Log.d("keydisp", "===================================================");
if (DBG) Log.d("keydisp", "Focused view Hierarchy is:");
debug();
if (DBG) Log.d("keydisp", "===================================================");
}
}
Message msg = obtainMessage(DISPATCH_KEY);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
if (LOCAL_LOGV) Log.v(
TAG, "sending key " + event + " to " + mView);
enqueueInputEvent(msg, event.getEventTime());
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
...
case FINISHED_EVENT:
handleFinishedEvent(msg.arg1, msg.arg2 != 0);
break;
case DISPATCH_KEY:
deliverKeyEvent((KeyEvent)msg.obj, msg.arg1 != 0);
break;
case DISPATCH_POINTER:
deliverPointerEvent((MotionEvent) msg.obj, msg.arg1 != 0);
break;deliverKeyEvent()函数的执行流程如下：
调用
mView.dispatchKeyEventPreIme()，如果有输入法存在，那么按键消息首先会被派发到输入法窗口，如果想在输入法截获消息之前处理该消息，那么可以重载该函数。imm.dispatchKeyEvent()将消息派发到输入法窗口调用
deliverKeyEventPostIme()继而调用到mView.dispatchKeyEvent()
private void deliverKeyEvent(KeyEvent event, boolean sendDone) {
if (ViewDebug.DEBUG_LATENCY) {
mInputEventDeliverTimeNanos = System.nanoTime();
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 0);
}
// If there is no view, then the event will not be handled.
if (mView == null || !mAdded) {
finishKeyEvent(event, sendDone, false);
return;
}
if (LOCAL_LOGV) Log.v(TAG, "Dispatching key " + event + " to " + mView);
// Perform predispatching before the IME.
if (mView.dispatchKeyEventPreIme(event)) {
finishKeyEvent(event, sendDone, true);
return;
}
// Dispatch to the IME before propagating down the view hierarchy.
// The IME will eventually call back into handleFinishedEvent.
if (mLastWasImTarget) {
InputMethodManager imm = InputMethodManager.peekInstance();
if (imm != null) {
int seq = enqueuePendingEvent(event, sendDone);
if (DEBUG_IMF) Log.v(TAG, "Sending key event to IME: seq="
+ seq + " event=" + event);
imm.dispatchKeyEvent(mView.getContext(), seq, event, mInputMethodCallback);
return;
}
}
// Not dispatching to IME, continue with post IME actions.
deliverKeyEventPostIme(event, sendDone);
}
private void deliverKeyEventPostIme(KeyEvent event, boolean sendDone) {
...
// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {
finishKeyEvent(event, sendDone, true);
return;
}
...
}mView对于应用窗口而言就是PhoneWindow.DecorView，否则就是普通的ViewGroup，我们只讨论DecorView中dispatchKeyEvent的实现：
处理系统快捷键
调用
View中Callback对象的dispatchKeyEvent()，即调用Activity的dispatchKeyEvent()如果
Activity没有消耗该消息，则调用PhoneWindow的OnKeyEvent()对消息做最后的处理
@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;
}
}
}
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);
}下面来具体看下Activity中dispatchKeyEvent的执行过程，首先来看源码：
public boolean dispatchKeyEvent(KeyEvent event) {
onUserInteraction();
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);
}主要过程如下：
调用
onUserInteraction()，可重载该函数在消息派发前做一些处理回调
Activity包含的Window对象的superDispatchKeyEvent，该函数继而调用mDecor.superDispatchKveyEent，该函数继而又调用super.dispatchKeyEvent，DecorView的父类是FrameLayout，而FrameLayout未重载dispatchKeyEvent，因此最终调用ViewGroup的dispatchKeyEvent如果
DecorView未消耗消息，则调用event的dispatch()函数，这里的第一个参数receiver是Activity对象
@Override
public boolean superDispatchKeyEvent(KeyEvent event) {
return mDecor.superDispatchKeyEvent(event);
}
public boolean superDispatchKeyEvent(KeyEvent event) {
if (super.dispatchKeyEvent(event)) {
return true;
}
// Not handled by the view hierarchy, does the action bar want it
// to cancel out of something special?
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;
}
// Next collapse any expanded action views.
if (mActionBar != null && mActionBar.hasExpandedActionView()) {
if (action == KeyEvent.ACTION_UP) {
mActionBar.collapseActionView();
}
return true;
}
}
return false;
}下面分析ViewGroup中dispatchKeyEvent的执行流程：如果ViewGroup本身拥有焦点，则调用super.dispatchKeyEvent把该消息派发到ViewGroup自身，如果其子视图拥有焦点，则调用mFocused.dispatchKeyEvent将消息派发给子视图，假如子视图也是ViewGroup，并且焦点是其子视图，则继续递归调用ViewGroup的dispatchKeyEvent
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 1);
}
if ((mPrivateFlags & (FOCUSED | HAS_BOUNDS)) == (FOCUSED | HAS_BOUNDS)) {
if (super.dispatchKeyEvent(event)) {
return true;
}
} else if (mFocused != null && (mFocused.mPrivateFlags & HAS_BOUNDS) == HAS_BOUNDS) {
if (mFocused.dispatchKeyEvent(event)) {
return true;
}
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 1);
}
return false;
}在View类的dispatchKeyEvent中首先回调onKey()函数，应用程序可重载该函数以实现自定义消息处理，如果onKey函数未消耗该消息，则调用event的dispatch函数，在调用该函数是，第一个参数receiver是View对象本身
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 0);
}
// Give any attached key listener a first crack at the event.
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) {
return true;
}
if (event.dispatch(this, mAttachInfo != null
? mAttachInfo.mKeyDispatchState : null, this)) {
return true;
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return false;
}如果拥有焦点的View没有处理该按键消息，则继续调用event.dispatch()函数：
/**
* Deliver this key event to a {@link Callback} interface. If this is
* an ACTION_MULTIPLE event and it is not handled, then an attempt will
* be made to deliver a single normal event.
*
* @param receiver The Callback that will be given the event.
* @param state State information retained across events.
* @param target The target of the dispatch, for use in tracking.
*
* @return The return value from the Callback method that was called.
*/
public final boolean dispatch(Callback receiver, DispatcherState state,
Object target) {
switch (mAction) {
case ACTION_DOWN: {
mFlags &= ~FLAG_START_TRACKING;
if (DEBUG) Log.v(TAG, "Key down to " + target + " in " + state
+ ": " + this);
boolean res = receiver.onKeyDown(mKeyCode, this);
if (state != null) {
if (res && mRepeatCount == 0 && (mFlags&FLAG_START_TRACKING) != 0) {
if (DEBUG) Log.v(TAG, " Start tracking!");
state.startTracking(this, target);
} else if (isLongPress() && state.isTracking(this)) {
try {
if (receiver.onKeyLongPress(mKeyCode, this)) {
if (DEBUG) Log.v(TAG, " Clear from long press!");
state.performedLongPress(this);
res = true;
}
} catch (AbstractMethodError e) {
}
}
}
return res;
}
case ACTION_UP:
if (DEBUG) Log.v(TAG, "Key up to " + target + " in " + state
+ ": " + this);
if (state != null) {
state.handleUpEvent(this);
}
return receiver.onKeyUp(mKeyCode, this);
case ACTION_MULTIPLE:
final int count = mRepeatCount;
final int code = mKeyCode;
if (receiver.onKeyMultiple(code, count, this)) {
return true;
}
if (code != KeyEvent.KEYCODE_UNKNOWN) {
mAction = ACTION_DOWN;
mRepeatCount = 0;
boolean handled = receiver.onKeyDown(code, this);
if (handled) {
mAction = ACTION_UP;
receiver.onKeyUp(code, this);
}
mAction = ACTION_MULTIPLE;
mRepeatCount = count;
return handled;
}
return false;
}
return false;
}该函数中主要根据相应的逻辑回调了receiver中的onKeyDown, onKeyUp, OnKeyLongPress, OnKeyMultiple函数。View中onKeyDown和onKeyUp有自己默认的处理，主要处理presse状态，长按检测，onCick回调。而OnKeyLongPress和OnKeyMultiple为空实现。对于Activity的OnKeyDown和onKeyUp函数主要实现按数字启动打电话程序（onKeyDown）以及back键的onBackPressed回调(onKeyUp)
如果按键消息在View树内部和Activity中没有被处理，就会调用到PhoneWindow的OnKeyDown和OnKeyUp函数，这是按键消息的最后处理机会，在PhoneWindow的OnKeyDown和OnKeyUp函数中主要处理了一些系统按键，例如音量键、音乐播放控制按键、照相机键、菜单键、拨号键、Search键等，具体代码就不再贴了。
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