本文主要是介绍Android Input输入系统之三：KeyEvent事件分发和上层应用层对事件的接收，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
相关参考：
《Android按键Input KeyEvent》
《Android Input输入系统之一：KeyEvent事件监听及事件分发流程》
《Android Input输入系统之二：KeyEvent注入事件及事件分发流程》
《Android Input输入系统之三：KeyEvent事件分发和上层应用层对事件的接收》
《Android Input输入系统之四：KeyEvent事件中的InputChannel通信》
《Android Input输入系统之五：按键调节音量加减》
在文章《Android Input输入系统之二：KeyEvent注入事件及事件分发流程》中，
InputDispatcherThread使用InputChannel的sendMessage方法发送了按键消息。
那么上层应用层是如何接收到按键消息的呢？
上层的应用在创建窗口的时候addView和addWindow的时候也创建了InputChannel，并且在WindowInputEventReceiver进行接收。
可以说，每个窗口的创建都需要经过addWindow().
\frameworks\base\services\core\java\com\android\server\wm\WindowManagerService.java
public class WindowManagerService extends IWindowManager.Stub implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {public int addWindow(Session session, IWindow client, int seq,LayoutParams attrs, int viewVisibility, int displayId, Rect outFrame,Rect outContentInsets, Rect outStableInsets, Rect outOutsets,DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel) {//省略一部分代码//...final boolean openInputChannels = (outInputChannel != null&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);if (openInputChannels) {win.openInputChannel(outInputChannel);}//省略一部分代码//...}
}
我们可以看到有一个InputChannel outInputChannel的参数。并且执行了openInputChannel，打开这个outInputChannel。
/** A window in the window manager. */
public class WindowState extends WindowContainer<WindowState> implements WindowManagerPolicy.WindowState {void openInputChannel(InputChannel outInputChannel) {if (mInputChannel != null) {throw new IllegalStateException("Window already has an input channel.");}String name = getName();InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);mInputChannel = inputChannels[0];mClientChannel = inputChannels[1];mInputWindowHandle.inputChannel = inputChannels[0];if (outInputChannel != null) {mClientChannel.transferTo(outInputChannel);mClientChannel.dispose();mClientChannel = null;} else {// If the window died visible, we setup a dummy input channel, so that taps// can still detected by input monitor channel, and we can relaunch the app.// Create dummy event receiver that simply reports all events as handled.mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);}mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);}@OverrideString getName() {return Integer.toHexString(System.identityHashCode(this))+ " " + getWindowTag();}CharSequence getWindowTag() {CharSequence tag = mAttrs.getTitle();if (tag == null || tag.length() <= 0) {tag = mAttrs.packageName;}return tag;}
}
可以发现，使用openInputChannelPair创建了一对InputChannel实例，名称就是window的title或者包名。
参数outInputChannel的来源，是在frameworks\base\core\java\android\view\ViewRootImpl.java的setView中创建了
mInputChannel = new InputChannel();并通过mWindowSession.addToDisplay()中传给WindowManagerService中的addWindow()
frameworks\base\core\java\android\view\ViewRootImpl.java
/*** We have one child*/
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {//省略一部分代码//...if (mInputChannel != null) {if (mInputQueueCallback != null) {mInputQueue = new InputQueue();mInputQueueCallback.onInputQueueCreated(mInputQueue);}mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,Looper.myLooper());}//省略一部分代码//...
}
接下来，ViewRootImpl中的setView()，做了两件事：
1.创建了一个InputQueue，它表示一个输入事件队列并设置事件回调。
2.创建一个WindowInputEventReceiver的实例负责读取事件。
WindowInputEventReceiver是ViewRootImpl的内部类，也是InputEventReceiver的子类：
final class WindowInputEventReceiver extends InputEventReceiver {public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {super(inputChannel, looper);}
}
frameworks\base\core\java\android\view\InputEventReceiver.java
//创建一个input事件接收器并绑定到指定的inputChannel中
public InputEventReceiver(InputChannel inputChannel, Looper looper) {if (inputChannel == null) {throw new IllegalArgumentException("inputChannel must not be null");}if (looper == null) {throw new IllegalArgumentException("looper must not be null");}mInputChannel = inputChannel;mMessageQueue = looper.getQueue();mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),inputChannel, mMessageQueue);mCloseGuard.open("dispose");
}
关键是调用了nativeInit方法，这个方法是一个native方法，实现在frameworks\base\core\jni\android_view_InputEventReceiver.cpp文件中。
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,jobject inputChannelObj, jobject messageQueueObj) {sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,inputChannelObj);if (inputChannel == NULL) {jniThrowRuntimeException(env, "InputChannel is not initialized.");return 0;}sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);if (messageQueue == NULL) {jniThrowRuntimeException(env, "MessageQueue is not initialized.");return 0;}sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,receiverWeak, inputChannel, messageQueue);//调用NativeInputEventReceiver的initialize()status_t status = receiver->initialize();if (status) {String8 message;message.appendFormat("Failed to initialize input event receiver. status=%d", status);jniThrowRuntimeException(env, message.string());return 0;}receiver->incStrong(gInputEventReceiverClassInfo.clazz); // retain a reference for the objectreturn reinterpret_cast<jlong>(receiver.get());
}
NativeInputEventReceiver定义在android_view_InputEventReceiver中，父类是LooperCallback。
这个方法中构造了NativeInputEventReceiver类的实例，并调用其initialize方法：
status_t NativeInputEventReceiver::initialize() {setFdEvents(ALOOPER_EVENT_INPUT);return OK;
}
void NativeInputEventReceiver::setFdEvents(int events) {if (mFdEvents != events) {mFdEvents = events;int fd = mInputConsumer.getChannel()->getFd();if (events) {mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);} else {mMessageQueue->getLooper()->removeFd(fd);}}
}
我们传入的Looper是我们主线程的Looper，这里调用了我们主线程Looper的getFd方法，addFd()是个关键的方法。
addFd()，设置了callback回调，使用epoll_ctl监听文件描述符，当收到事件后，回调NativeInputEventReceiver的handleEvent();
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {if (events & (ALOOPER_EVENT_ERROR | ALOOPER_EVENT_HANGUP)) {// This error typically occurs when the publisher has closed the input channel// as part of removing a window or finishing an IME session, in which case// the consumer will soon be disposed as well.if (kDebugDispatchCycle) {ALOGD("channel '%s' ~ Publisher closed input channel or an error occurred. ""events=0x%x", getInputChannelName().c_str(), events);}return 0; // remove the callback}if (events & ALOOPER_EVENT_INPUT) {JNIEnv* env = AndroidRuntime::getJNIEnv();status_t status = consumeEvents(env, false /*consumeBatches*/, -1, NULL);mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");return status == OK || status == NO_MEMORY ? 1 : 0;}if (events & ALOOPER_EVENT_OUTPUT) {for (size_t i = 0; i < mFinishQueue.size(); i++) {const Finish& finish = mFinishQueue.itemAt(i);status_t status = mInputConsumer.sendFinishedSignal(finish.seq, finish.handled);if (status) {mFinishQueue.removeItemsAt(0, i);if (status == WOULD_BLOCK) {if (kDebugDispatchCycle) {ALOGD("channel '%s' ~ Sent %zu queued finish events; %zu left.",getInputChannelName().c_str(), i, mFinishQueue.size());}return 1; // keep the callback, try again later}ALOGW("Failed to send finished signal on channel '%s'. status=%d",getInputChannelName().c_str(), status);if (status != DEAD_OBJECT) {JNIEnv* env = AndroidRuntime::getJNIEnv();String8 message;message.appendFormat("Failed to finish input event. status=%d", status);jniThrowRuntimeException(env, message.string());mMessageQueue->raiseAndClearException(env, "finishInputEvent");}return 0; // remove the callback}}if (kDebugDispatchCycle) {ALOGD("channel '%s' ~ Sent %zu queued finish events; none left.",getInputChannelName().c_str(), mFinishQueue.size());}mFinishQueue.clear();setFdEvents(ALOOPER_EVENT_INPUT);return 1;}ALOGW("channel '%s' ~ Received spurious callback for unhandled poll event. ""events=0x%x", getInputChannelName().c_str(), events);return 1;
}
其中调用了consumeEvents()方法。consumeEvents()实则调用了InputEventReceiver.java中的dispatchInputEvent()
// Called from native code.
@SuppressWarnings("unused")
private void dispatchInputEvent(int seq, InputEvent event, int displayId) {mSeqMap.put(event.getSequenceNumber(), seq);onInputEvent(event, displayId);
}public void onInputEvent(InputEvent event, int displayId) {finishInputEvent(event, false);
}WindowInputEventReceiver复写了onInputEvent，实际调用的是WindowInputEventReceiver中的onInputEvent()方法。@Override
public void onInputEvent(InputEvent event, int displayId) {enqueueInputEvent(event, this, 0, true);
}void enqueueInputEvent(InputEvent event,InputEventReceiver receiver, int flags, boolean processImmediately) {adjustInputEventForCompatibility(event);QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);// Always enqueue the input event in order, regardless of its time stamp.// We do this because the application or the IME may inject key events// in response to touch events and we want to ensure that the injected keys// are processed in the order they were received and we cannot trust that// the time stamp of injected events are monotonic.QueuedInputEvent last = mPendingInputEventTail;if (last == null) {mPendingInputEventHead = q;mPendingInputEventTail = q;} else {last.mNext = q;mPendingInputEventTail = q;}mPendingInputEventCount += 1;Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,mPendingInputEventCount);if (processImmediately) {doProcessInputEvents();} else {scheduleProcessInputEvents();}
}
调用了doProcessInputEvents()
void doProcessInputEvents() {// Deliver all pending input events in the queue.while (mPendingInputEventHead != null) {QueuedInputEvent q = mPendingInputEventHead;mPendingInputEventHead = q.mNext;if (mPendingInputEventHead == null) {mPendingInputEventTail = null;}q.mNext = null;mPendingInputEventCount -= 1;Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,mPendingInputEventCount);long eventTime = q.mEvent.getEventTimeNano();long oldestEventTime = eventTime;if (q.mEvent instanceof MotionEvent) {MotionEvent me = (MotionEvent)q.mEvent;if (me.getHistorySize() > 0) {oldestEventTime = me.getHistoricalEventTimeNano(0);}}mChoreographer.mFrameInfo.updateInputEventTime(eventTime, oldestEventTime);deliverInputEvent(q);}// We are done processing all input events that we can process right now// so we can clear the pending flag immediately.if (mProcessInputEventsScheduled) {mProcessInputEventsScheduled = false;mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);}
}
处理逻辑在deliverInputEvent()中，
private void deliverInputEvent(QueuedInputEvent q) {Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, "deliverInputEvent",q.mEvent.getSequenceNumber());if (mInputEventConsistencyVerifier != null) {mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);}InputStage stage;if (q.shouldSendToSynthesizer()) {stage = mSyntheticInputStage;} else {stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;}if (q.mEvent instanceof KeyEvent) {mUnhandledKeyManager.preDispatch((KeyEvent) q.mEvent);}if (stage != null) {handleWindowFocusChanged();stage.deliver(q);} else {finishInputEvent(q);}
}
之前setView()中时，创建了mSyntheticInputStage，
// Set up the input pipeline.
CharSequence counterSuffix = attrs.getTitle();
mSyntheticInputStage = new SyntheticInputStage();
InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,"aq:native-post-ime:" + counterSuffix);
InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
InputStage imeStage = new ImeInputStage(earlyPostImeStage,"aq:ime:" + counterSuffix);
InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,"aq:native-pre-ime:" + counterSuffix);mFirstInputStage = nativePreImeStage;
mFirstPostImeInputStage = earlyPostImeStage;
mPendingInputEventQueueLengthCounterName = "aq:pending:" + counterSuffix;
在这里：
stage = mSyntheticInputStage;
stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
stage.deliver(q);
所以，这里又三个阶段，stage可能是ViewPostImeInputStage()对象，也有可能是EarlyPostImeInputStage()，也有可能是ViewPreImeInputStage();这里分析其中一个ViewPreImeInputStage()
这几个类中都有onProcess();并且都是继承了InputStage
abstract class InputStage {/*** Delivers an event to be processed.*/public final void deliver(QueuedInputEvent q) {if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {forward(q);} else if (shouldDropInputEvent(q)) {finish(q, false);} else {apply(q, onProcess(q));}}
}/*** Delivers pre-ime input events to the view hierarchy.* Does not support pointer events.*/
final class ViewPreImeInputStage extends InputStage {public ViewPreImeInputStage(InputStage next) {super(next);}@Overrideprotected int onProcess(QueuedInputEvent q) {if (q.mEvent instanceof KeyEvent) {return processKeyEvent(q);}return FORWARD;}private int processKeyEvent(QueuedInputEvent q) {final KeyEvent event = (KeyEvent)q.mEvent;if (mView.dispatchKeyEventPreIme(event)) {return FINISH_HANDLED;}return FORWARD;}
}
deliver(q)，会调用每个InputStage子类的onProcess(),
执行processKeyEvent()
private int processKeyEvent(QueuedInputEvent q) {final KeyEvent event = (KeyEvent)q.mEvent;if (mView.dispatchKeyEventPreIme(event)) {return FINISH_HANDLED;}return FORWARD;
}
mView.dispatchKeyEventPreIme(event),分发了事件到View中。
dispatchKeyEventPreIme是在输入法弹出界面时，响应的方法。
当到了ViewPostImeInputStage阶段，执行的processKeyEvent(),会调用：
// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {
return FINISH_HANDLED;
}
将按键消息传递到view结构。
总结
其中，最重要的流程还是NativeInputEventReceiver中的handleEvent()回调。
具体源码还得研究Looper是如何进行回调的。
另外：
void NativeInputEventReceiver::setFdEvents(int events) {
if (mFdEvents != events) {
mFdEvents = events;
int fd = mInputConsumer.getChannel()->getFd();
if (events) {
mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);
} else {
mMessageQueue->getLooper()->removeFd(fd);
}
}
}
Looper中进行监听的文件描述符getFd();
int fd = mInputConsumer.getChannel()->getFd();
其中mInputConsumer.getChannel()来自与nativeInit()中的：
sp inputChannel = android_view_InputChannel_getInputChannel(env, inputChannelObj);
流程图：
图片来源于：
参考资料：
https://www.jianshu.com/p/f05d6b05ba17
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