Android：输入系统(InputChannel)

http://blog.csdn.net/itleaks/article/details/27165657

前面的“锤子快捷键”相关文章已经分析了输入事件的读取，处理，分发。我们知道事件的传递是以window为单位传递的，即server只负责将事件传递给某一个或者多个window，window然后再将事件传递给某一个具体的view。一个activity或者dialog对应一个window，但是事件只传递给合适的window，比如对于按键事件，就必须是获得焦点的window,也就是说只能传递给一个window,通常是最上面的程序。找到了合适的window,然后就是将事件添加到window的Connection的事件队列上。其实，到这为止输入事件还只是在server端，即system_server这个进程里，要想让程序获取到事件，肯定必须将事件信息传递到程序端的进程里。这个就是Connection的实现问题了，这个connection的真正逻辑是InputChannel, InputChannel其实就是linux unix socket的一种封装, unixsocket是linux的一种跨进程通信方式。系统创建InputChannel对即unix socket对，系统server端和程序client各只有其中一个，这样通过unix socket就可以给对方发送消息，而这里的事件就是通过这种方式从系统进程传递到程序进程的。整个系统框架图如下：

系统server端的InputChannel

系统InputChannel的整个处理逻辑如下：

Server端 InputChannel的创建

Server端 InputChannel是在window被创建的时候创建的：

    //addWindow会创建一个channel对，其实上就是unix socket对，其中一个unix socket    //通过传入参数outInputChannel被传递到程序端,    //另外一个unix socket保存在server的window中并注册到native的InputManager    public int addWindow(Session session, IWindow client, int seq,            WindowManager.LayoutParams attrs, int viewVisibility, int displayId,            Rect outContentInsets, InputChannel outInputChannel) {            //创建window的数据对象WindowState            win = new WindowState(this, session, client, token,                    attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);            if (outInputChannel != null && (attrs.inputFeatures &                 WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {                String name = win.makeInputChannelName();                //创建channel对，即会返回两个InputChannel                InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);                //一个unix socket保存到window里                win.setInputChannel(inputChannels[0]);                //另外一个unix socket传递到程序端                inputChannels[1].transferTo(outInputChannel);                //这个函数很重要，这个会将server端的unix socket注册到native层                //的InputManager,  win.mInputChannel就是上面的inputChannels[0]                mInputManager.registerInputChannel(win.mInputChannel,                        win.mInputWindowHandle);            }        }        return res;}public static InputChannel[] openInputChannelPair(String name) {        return nativeOpenInputChannelPair(name);}static jobjectArray android_view_InputChannel_nativeOpenInputChannelPair(JNIEnv* env,        jclass clazz, jstring nameObj) {    sp<InputChannel> serverChannel;    sp<InputChannel> clientChannel;     //创建input channel对    status_t result = InputChannel::openInputChannelPair(name,          serverChannel, clientChannel);    jobjectArray channelPair = env->NewObjectArray(2, gInputChannelClassInfo.clazz, NULL);    //创建inputChannel对应的java对象    jobject serverChannelObj = android_view_InputChannel_createInputChannel(env,            new NativeInputChannel(serverChannel));    jobject clientChannelObj = android_view_InputChannel_createInputChannel(env,            new NativeInputChannel(clientChannel));    //将两个channel放到channel数组中    env->SetObjectArrayElement(channelPair, 0, serverChannelObj);    env->SetObjectArrayElement(channelPair, 1, clientChannelObj);    return channelPair;}//InputTransport.cppstatus_t InputChannel::openInputChannelPair(const String8& name,        sp<InputChannel>& outServerChannel, sp<InputChannel>& outClientChannel) {    int sockets[2];    //很早的android 版本是使用双向管道实现的，而是现在是使用unix socket双通道    //来通信    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {        return result;    }    int bufferSize = SOCKET_BUFFER_SIZE;    setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));    setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));    setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));    setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));    String8 serverChannelName = name;    serverChannelName.append(" (server)");    //创建InputChannel，并把通信文件句柄传入    outServerChannel = new InputChannel(serverChannelName, sockets[0]);    String8 clientChannelName = name;    clientChannelName.append(" (client)");    //创建InputChannel，并把通信文件句柄传入    outClientChannel = new InputChannel(clientChannelName, sockets[1]);    return OK;}

Server端 InputChannel事件监听器安装

InputDispatcher要能够发送事件数据，必须的要让其知道对应的window的InputChannel，这个通过注册实现的。

 public void registerInputChannel(InputChannel inputChannel,            InputWindowHandle inputWindowHandle) {                nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);}status_t NativeInputManager::registerInputChannel(JNIEnv* env,        const sp<InputChannel>& inputChannel,        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {    //调用InputDispatcher的函数    return mInputManager->getDispatcher()->registerInputChannel(            inputChannel, inputWindowHandle, monitor);}status_t InputDispatcher::registerInputChannel(const sp<InputChannel>& inputChannel,        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {    { // acquire lock        AutoMutex _l(mLock);        //这个将inputChannel封装为Connection        sp<Connection> connection = new Connection(inputChannel, inputWindowHandle, monitor);            //这个就是unix socket文件句柄        int fd = inputChannel->getFd();        //将connection保存到映射表中        mConnectionsByFd.add(fd, connection);        //监听该unix socket文件，当unix socket有数据时即client发送消息过来了，        //函数handleReceiveCallback就会被执行        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);    } // release lock    // Wake the looper because some connections have changed.    mLooper->wake();    return OK;}

Server端的InputChannel事件数据发送

在上几篇文章“锤子快捷键配置”中，已经讲到了事件分发，并最后将事件放到了connection的事件队列中，InputChannel事件发送就是从开始的

void InputDispatcher::enqueueDispatchEntriesLocked(nsecs_t currentTime,        const sp<Connection>& connection, EventEntry* eventEntry, const InputTarget* inputTarget) {    bool wasEmpty = connection->outboundQueue.isEmpty();    // Enqueue dispatch entries for the requested modes.    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_HOVER_EXIT);    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_OUTSIDE);    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_HOVER_ENTER);    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_IS);    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_SLIPPERY_EXIT);    enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,            InputTarget::FLAG_DISPATCH_AS_SLIPPERY_ENTER);    // 原来是空，现在不空，则立刻分发事件    if (wasEmpty && !connection->outboundQueue.isEmpty()) {        startDispatchCycleLocked(currentTime, connection);    }} void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,        const sp<Connection>& connection) {    //遍历所有发送队列中的事件    while (connection->status == Connection::STATUS_NORMAL            && !connection->outboundQueue.isEmpty()) {        //获取最早的需要发送的事件        DispatchEntry* dispatchEntry = connection->outboundQueue.head;        EventEntry* eventEntry = dispatchEntry->eventEntry;        switch (eventEntry->type) {        case EventEntry::TYPE_KEY: {            KeyEntry* keyEntry = static_cast<KeyEntry*>(eventEntry);            //真正发送事件.            status = connection->inputPublisher.publishKeyEvent(dispatchEntry->seq,                    keyEntry->deviceId, keyEntry->source,                    dispatchEntry->resolvedAction, dispatchEntry->resolvedFlags,                    keyEntry->keyCode, keyEntry->scanCode,                    keyEntry->metaState, keyEntry->repeatCount, keyEntry->downTime,                    keyEntry->eventTime);            break;        }        // Check the result.        if (status) {            if (status == WOULD_BLOCK) {                if (connection->waitQueue.isEmpty()) {                } else {                    connection->inputPublisherBlocked = true;                }            }            //发送成功，返回执行下一次循环            return;        }        // 事件发送失败，重新放进待发送队列        connection->outboundQueue.dequeue(dispatchEntry);        connection->waitQueue.enqueueAtTail(dispatchEntry);    }}status_t InputPublisher::publishKeyEvent(        uint32_t seq,        int32_t deviceId,        int32_t source,        int32_t action,        int32_t flags,        int32_t keyCode,        int32_t scanCode,        int32_t metaState,        int32_t repeatCount,        nsecs_t downTime,        nsecs_t eventTime) {    InputMessage msg;    //将输入事件转化为unix socket通信的格式    msg.header.type = InputMessage::TYPE_KEY;    msg.body.key.seq = seq;    msg.body.key.deviceId = deviceId;    msg.body.key.source = source;    msg.body.key.action = action;    msg.body.key.flags = flags;    msg.body.key.keyCode = keyCode;    msg.body.key.scanCode = scanCode;    msg.body.key.metaState = metaState;    msg.body.key.repeatCount = repeatCount;    msg.body.key.downTime = downTime;msg.body.key.eventTime = eventTime;    //调用unix socket消息发送机制    return mChannel->sendMessage(&msg);}status_t InputChannel::sendMessage(const InputMessage* msg) {    size_t msgLength = msg->size();    ssize_t nWrite;do {    //通过unix socket将事件数据发送到程序端        nWrite = ::send(mFd, msg, msgLength, MSG_DONTWAIT | MSG_NOSIGNAL);    } while (nWrite == -1 && errno == EINTR);    return OK;}

程序client端的InputChannel

client的InputChannel相关的处理逻辑如下：

Client 端的InputChannel创建

Client接受事件，肯定必须先获得inputChannel，这个是在addWindow时系统返回回来的。

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {        synchronized (this) {                if ((mWindowAttributes.inputFeatures&                   WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {                    mInputChannel = new InputChannel();                }                try {                    //该函数会返回一个InputChannel                    res = mWindowSession.addToDisplay(mWindow, mSeq,                            mWindowAttributes,                            getHostVisibility(), mDisplay.getDisplayId(),                            mAttachInfo.mContentInsets, mInputChannel);                }                if (mInputChannel != null) {                    if (mInputQueueCallback != null) {                        mInputQueue = new InputQueue();                        mInputQueueCallback.onInputQueueCreated(mInputQueue);                    }                    //为InputChannel注册监听器                    mInputEventReceiver = new WindowInputEventReceiver(                         mInputChannel,                         Looper.myLooper());                }<pre name="code" class="java" style="font-size: 14px;">          }

Client端的 InputChannel监听器安装

InputChannel监听器安装在WindowInputEventReceiver初始化的时候

final class WindowInputEventReceiver extends InputEventReceiver {        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {            super(inputChannel, looper);        }}public InputEventReceiver(InputChannel inputChannel, Looper looper) {        mInputChannel = inputChannel;        mMessageQueue = looper.getQueue();        mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),                inputChannel, mMessageQueue);        mCloseGuard.open("dispose"); }static jint nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,        jobject inputChannelObj, jobject messageQueueObj) {    //获取native层的InputChannel    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,            inputChannelObj);    //获取java层InputEventReceiver对象的native层的消息队列    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);        //创建native对应的InputEventReceiver对象    sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,            receiverWeak, inputChannel, messageQueue);    //这个是真正安装监听的函数    status_t status = receiver->initialize();    return reinterpret_cast<jint>(receiver.get());}status_t NativeInputEventReceiver::initialize() {    //安装监听器    setFdEvents(ALOOPER_EVENT_INPUT);    return OK;}void NativeInputEventReceiver::setFdEvents(int events) {    if (mFdEvents != events) {        mFdEvents = events;        int fd = mInputConsumer.getChannel()->getFd();        if (events) {           //用looper监听inputChannel对应的unix socket文件句柄            mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);        }    }}int Looper::addFd(int fd, int ident, int events, ALooper_callbackFunc callback, void* data) {    return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);}int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {    { // acquire lock        AutoMutex _l(mLock);        //将监听参数封装        Request request;        request.fd = fd;        request.ident = ident;        //这个很重要，当被监听的文件发生变化时就会调用该callback函数        request.callback = callback;        request.data = data;        ssize_t requestIndex = mRequests.indexOfKey(fd);        if (requestIndex < 0) {            //epoll该文件，也就是讲unix socket文件添加到监听文件列表中            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);            mRequests.add(fd, request);        }    } // release lock    return 1;}

Client端的InputChannel中的事件接收

从上面可以看出，Java的InputEventReceiver层的native层的NativeInputEventReceiver负责监听事件，当有事件时，就会调用它。

int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData) {    int result = 0;    for (;;) {        while (mResponseIndex < mResponses.size()) {            const Response& response = mResponses.itemAt(mResponseIndex++);            int ident = response.request.ident;            if (ident >= 0) {                int fd = response.request.fd;                int events = response.events;                void* data = response.request.data;                if (outFd != NULL) *outFd = fd;                if (outEvents != NULL) *outEvents = events;                if (outData != NULL) *outData = data;                return ident;            }        }        result = pollInner(timeoutMillis);    }}int Looper::pollInner(int timeoutMillis) {    struct epoll_event eventItems[EPOLL_MAX_EVENTS];    //等待消息    int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);    for (int i = 0; i < eventCount; i++) {        int fd = eventItems[i].data.fd;        uint32_t epollEvents = eventItems[i].events;        if (fd == mWakeReadPipeFd) {            if (epollEvents & EPOLLIN) {                awoken();            }        } else {            ssize_t requestIndex = mRequests.indexOfKey(fd);            if (requestIndex >= 0) {                int events = 0;                if (epollEvents & EPOLLIN) events |= ALOOPER_EVENT_INPUT;                if (epollEvents & EPOLLOUT) events |= ALOOPER_EVENT_OUTPUT;                if (epollEvents & EPOLLERR) events |= ALOOPER_EVENT_ERROR;                if (epollEvents & EPOLLHUP) events |= ALOOPER_EVENT_HANGUP;                //将事件放到事件队列上                pushResponse(events, mRequests.valueAt(requestIndex));            }        }    }Done: ;    //处理前面加入的response事件    for (size_t i = 0; i < mResponses.size(); i++) {        Response& response = mResponses.editItemAt(i);        if (response.request.ident == ALOOPER_POLL_CALLBACK) {            int fd = response.request.fd;            int events = response.events;            void* data = response.request.data;            // 下面的callback就是 NativeInputEventRecieverd            int callbackResult = response.request.callback->handleEvent(fd, events, data);            if (callbackResult == 0) {                removeFd(fd);            }            response.request.callback.clear();            result = ALOOPER_POLL_CALLBACK;        }    }    return result;}int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {if (events & ALOOPER_EVENT_INPUT) {        JNIEnv* env = AndroidRuntime::getJNIEnv();        //处理事件        status_t status = consumeEvents(env, false /*consumeBatches*/, -1, NULL);        mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");        return status == OK || status == NO_MEMORY ? 1 : 0;}    return 1;}status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,        bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {    for (;;) {        uint32_t seq;        InputEvent* inputEvent;        //从buffer中还原出事件        status_t status = mInputConsumer.consume(&mInputEventFactory,                consumeBatches, frameTime, &seq, &inputEvent);        if (!skipCallbacks) {            jobject inputEventObj;            switch (inputEvent->getType()) {            case AINPUT_EVENT_TYPE_KEY:                //转换为java层的InputEvent                inputEventObj = android_view_KeyEvent_fromNative(env,                        static_cast<KeyEvent*>(inputEvent));                break;            }            if (inputEventObj) {                //这个就会调用到java层的函数InputEventReceiver->dispatchInputEvent                env->CallVoidMethod(receiverObj.get(),                        gInputEventReceiverClassInfo.dispatchInputEvent, seq, inputEventObj);            }        }    }}

Client端对输入事件的处理

输入事件，比如按键事件并不是全部被window的view处理了，比如Back键，如果此时系统输入法是显示的，其实该键首先会去关闭输入法，而window的view是接收不到这个键的，这个就是事件处理器链实现的,这个链上又各种处理器，它们按照处理的优先顺序添加咋链表上

输入事件处理链

public abstract class InputEventReceiver {    //native收到输入事件是最终会回调到该函数    private void dispatchInputEvent(int seq, InputEvent event) {        mSeqMap.put(event.getSequenceNumber(), seq);        onInputEvent(event);    }}   final class WindowInputEventReceiver extends InputEventReceiver {        @Override        public void onInputEvent(InputEvent event) {            enqueueInputEvent(event, this, 0, true);        }    }    void enqueueInputEvent(InputEvent event) {        enqueueInputEvent(event, null, 0, false);    }    void enqueueInputEvent(InputEvent event,            InputEventReceiver receiver, int flags, boolean processImmediately) {        QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);        QueuedInputEvent last = mPendingInputEventTail;        if (last == null) {            mPendingInputEventHead = q;            mPendingInputEventTail = q;        } else {            last.mNext = q;            mPendingInputEventTail = q;        }        mPendingInputEventCount += 1;        if (processImmediately) {            //处理事件            doProcessInputEvents();        } else {            scheduleProcessInputEvents();        }    }    void doProcessInputEvents() {        // 遍历所有的输入事件        while (mPendingInputEventHead != null) {            QueuedInputEvent q = mPendingInputEventHead;            mPendingInputEventHead = q.mNext;            if (mPendingInputEventHead == null) {                mPendingInputEventTail = null;            }            q.mNext = null;            mPendingInputEventCount -= 1;            //处理事件            deliverInputEvent(q);        }    }    private void deliverInputEvent(QueuedInputEvent q) {        try {            //检测ime相关module是否需要处理该输入事件，比如back键,是需要先            //让IME处理，这个时候需要先交给mFirstPostImeInputStage处理            InputStage stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;            if (stage != null) {                stage.deliver(q);            } else {                //                finishInputEvent(q);            }        }    }       //大部分时候stage= mFirstInputStage，这个变量在最开始的时候赋值       InputStage syntheticInputStage = new SyntheticInputStage();       InputStage viewPostImeStage = new ViewPostImeInputStage(syntheticInputStage);       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;<div>       abstract class InputStage {        public final void deliver(QueuedInputEvent q) {            if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {                //已经被处理了，则让后面的处理                forward(q);            } else if (shouldDropInputEvent(q)) {                finish(q, false);            } else {                //没有处理，自己开始处理该事件                apply(q, onProcess(q));            }        }        protected void apply(QueuedInputEvent q, int result) {            if (result == FORWARD) {                forward(q);            } else if (result == FINISH_HANDLED) {                finish(q, true);            }        }        protected void forward(QueuedInputEvent q) {            onDeliverToNext(q);        }        protected void onDeliverToNext(QueuedInputEvent q) {            //如果下一个事件处理器不为空，则让下一个事件处理器处理            if (mNext != null) {                mNext.deliver(q);            } else {               //所有的都处理器都完成了处理，调用finish告知server端事件已经被处理                finishInputEvent(q);            }        }}    //将事件发送给view的事件处理器是ViewPostImeInputStage    final class ViewPostImeInputStage extends InputStage {        @Override        protected int onProcess(QueuedInputEvent q) {            if (q.mEvent instanceof KeyEvent) {                return processKeyEvent(q);            }        }        private int processKeyEvent(QueuedInputEvent q) {            final KeyEvent event = (KeyEvent)q.mEvent;            if (event.getAction() != KeyEvent.ACTION_UP) {                // If delivering a new key event, make sure the window is                // now allowed to start updating.                handleDispatchDoneAnimating();            }            // 向view发送按键事件            if (mView.dispatchKeyEvent(event)) {                return FINISH_HANDLED;            }            // 系统默认按键处理，比如CAMERA快捷键处理            if (mFallbackEventHandler.dispatchKeyEvent(event)) {                return FINISH_HANDLED;            }            return FORWARD;        }    } 

从上面的逻辑可以看出处理器的处理有限顺序是:
NativePreImeInputStage->ViewPreImeInputStage-> ImeInputStage->
EarlyPostImeInputStage-> NativePostImeInputStage->ViewPostImeInputStage->
SyntheticInputStage

Back按键如何结束Activity

刚刚前面说到，view获得输入事件是由ViewPostImeInputStage传递过来的。ViewPostImeInputStage会将事件传递给activity的根View —DecorView

   private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {        @Override        public boolean dispatchKeyEvent(KeyEvent event) {            if (!isDestroyed()) {                //首先让callback处理，然后调用super的接口                final Callback cb = getCallback() && 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);        }   }   //上面的getCallback的返回值就是Activity，故其有很高的优先级获取并处理这些按键。   public boolean onKeyDown(int keyCode, KeyEvent event)  {        if (keyCode == KeyEvent.KEYCODE_BACK) {            if (getApplicationInfo().targetSdkVersion                    >= Build.VERSION_CODES.ECLAIR) {            } else {                //这个就是结束activity的函数                onBackPressed();            }            return true;        }    }

如果非back按键，则会调用super即View.dispatchKeyEvent的接口，view的事件接收及处理就是从这开始的。

View如何获取按键

由于DecorView继承FrameLayout，它自然是一个ViewGroup,所以我们来看下ViewGroup的dispatchKeyEvent。

    @Override    public boolean dispatchKeyEvent(KeyEvent event) {        if (mInputEventConsistencyVerifier != null) {            mInputEventConsistencyVerifier.onKeyEvent(event, 1);        }        if ((mPrivateFlags & (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS))                == (PFLAG_FOCUSED | PFLAG_HAS_BOUNDS)) {            //调用view的接口            if (super.dispatchKeyEvent(event)) {                return true;            }        } else if (mFocused != null && (mFocused.mPrivateFlags & PFLAG_HAS_BOUNDS)                == PFLAG_HAS_BOUNDS) {            //向获得焦点的view传递事件            if (mFocused.dispatchKeyEvent(event)) {                return true;            }        }        return false;    }    public boolean dispatchKeyEvent(KeyEvent event) {        if (event.dispatch(this, mAttachInfo != null                ? mAttachInfo.mKeyDispatchState : null, this)) {            return true;        }        return false;    }    public final boolean dispatch(Callback receiver, DispatcherState state,            Object target) {        switch (mAction) {            case ACTION_DOWN: {                mFlags &= ~FLAG_START_TRACKING;                //这个就是我们的常见的onKeyDown,onKeyUp接口的调用                boolean res = receiver.onKeyDown(mKeyCode, this);                return res;            }        }        return false;    }

Camera等快捷键是如何传递处理的

如果view没有处理按键，则最后会给mFallbackEventHandler一个机会处理按键，Camera等快捷键就是由这个handler处理的，下面来看看。

 public ViewRootImpl(Context context, Display display) {       mFallbackEventHandler= PolicyManager.makeNewFallbackEventHandler(context);}public class Policy implements IPolicy {public FallbackEventHandler makeNewFallbackEventHandler(Context context) {   return new PhoneFallbackEventHandler(context);}}public class PhoneFallbackEventHandler implements FallbackEventHandler {    public boolean dispatchKeyEvent(KeyEvent event) {        final int action = event.getAction();        final int keyCode = event.getKeyCode();        if (action == KeyEvent.ACTION_DOWN) {            return onKeyDown(keyCode, event);        } else {            return onKeyUp(keyCode, event);        }    }    boolean onKeyDown(int keyCode, KeyEvent event) {        switch (keyCode) {            case KeyEvent.KEYCODE_CAMERA: {                if (event.getRepeatCount() == 0) {                } else if (event.isLongPress() && dispatcher.isTracking(event)) {                    //启动拍照程序                    Intent intent = new Intent(Intent.ACTION_CAMERA_BUTTON, null);                    intent.putExtra(Intent.EXTRA_KEY_EVENT, event);                    mContext.sendOrderedBroadcastAsUser(intent, UserHandle.CURRENT_OR_SELF,                            null, null, null, 0, null, null);                }                return true;            }        }        return false;    }

输入事件处理完成通知

client将事件处理完了，必须通知server已经完成对该事件的处理，否则server一直在等待事件完成而不能发送后面的事件。

private void finishInputEvent(QueuedInputEvent q) {        if (q.mReceiver != null) {            boolean handled = (q.mFlags & QueuedInputEvent.FLAG_FINISHED_HANDLED) != 0;                          // mReceiver是InputEventReciever            q.mReceiver.finishInputEvent(q.mEvent, handled);        }        recycleQueuedInputEvent(q);}public abstract class InputEventReceiver {    public final void finishInputEvent(InputEvent event, boolean handled) {        {            int index = mSeqMap.indexOfKey(event.getSequenceNumber());            if (index < 0) {            } else {                //又调回native层                nativeFinishInputEvent(mReceiverPtr, seq, handled);            }        }        event.recycleIfNeededAfterDispatch();    }}status_t NativeInputEventReceiver::finishInputEvent(uint32_t seq, bool handled) {    //告知server端client已经处理完成inputEvent    status_t status = mInputConsumer.sendFinishedSignal(seq, handled);    return status;}status_t InputConsumer::sendFinishedSignal(uint32_t seq, bool handled) {    size_t seqChainCount = mSeqChains.size();    if (seqChainCount) {        uint32_t currentSeq = seq;        uint32_t chainSeqs[seqChainCount];        size_t chainIndex = 0;        for (size_t i = seqChainCount; i-- > 0; ) {             const SeqChain& seqChain = mSeqChains.itemAt(i);             if (seqChain.seq == currentSeq) {                 currentSeq = seqChain.chain;                 chainSeqs[chainIndex++] = currentSeq;                 mSeqChains.removeAt(i);             }        }        status_t status = OK;        while (!status && chainIndex-- > 0) {            status = sendUnchainedFinishedSignal(chainSeqs[chainIndex], handled);        }    }    // Send finished signal for the last message in the batch.    return sendUnchainedFinishedSignal(seq, handled);}status_t InputConsumer::sendUnchainedFinishedSignal(uint32_t seq, bool handled) {    InputMessage msg;    msg.header.type = InputMessage::TYPE_FINISHED;    msg.body.finished.seq = seq;    msg.body.finished.handled = handled;    return mChannel->sendMessage(&msg);}//这个和server端发送事件过来一样的，只不过这次是client发送消息给serverstatus_t InputChannel::sendMessage(const InputMessage* msg) {    size_t msgLength = msg->size();    ssize_t nWrite;    do {        nWrite = ::send(mFd, msg, msgLength, MSG_DONTWAIT | MSG_NOSIGNAL);    } while (nWrite == -1 && errno == EINTR);    return OK;}