Android事件分发的事件由来原理分析

目录

• Andriod事件分发的事件从何而来
• 调用WMS中的成员mInputManager
• 调用的mNative的方法
• 看看InputManager怎么初始化
• createInputChannel干了3件事
• 首先看下openInputChannelPair
• 回到createInputChannel中

Andriod事件分发的事件从何而来

上一篇最后留下了一个疑问，WMS的事件是哪里来的？

注册事件回调是通过mWindowSession.addToDisplayAsUser来实现的，这是一个Binder调用实际调用的是frameworks/base/services/core/java/com/android/server/wm/Session.java这个类。

 //frameworks/base/services/core/java/com/android/server/wm/Session.java
  @Override
    public int addToDisplayAsUser(IWindow window, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, int userId, InsetsVisibilities requestedVisibilities,
            InputChannel outInputChannel, InsetsState outInsetsState,
            InsetsSourceControl[] outActiveControls, Rect outAttachedFrame,
            float[] outSizeCompatScale) {
        return mService.addWindow(this, window, attrs, viewVisibility, displayId, userId,
                requestedVisibilities, outInputChannel, outInsetsState, outActiveControls,
                outAttachedFrame, outSizeCompatScale);
    }
​

这里的mService就是WMS.调用的就是WMS的addWindow,addWindow方法很长，其中与事件相关的就两行

//frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java
......
  final WindowState win = new WindowState(this, session, client, token, parentWindow,appOp[0], attrs, viewVisibility, session.mUid, userId,session.mCanAddInternalSystemWindow);
  win.openInputChannel(outInputChannel);

//frameworks/base/services/core/java/com/android/server/wm/WindowState.java
void openInputChannel(InputChannel outInputChannel) {
        if (mInputChannel != null) {
            throw new IllegalStateException("Window already has an input channel.");
        }
        String name = getName();
        mInputChannel = mWmService.mInputManager.createInputChannel(name);
        mInputChannelToken = mInputChannel.getToken();
        mInputWindowHandle.setToken(mInputChannelToken);
        mWmService.mInputToWindowMap.put(mInputChannelToken, this);
        if (outInputChannel != null) {
          //将native创建的InputChannel复制给参数outInputChannel
            mInputChannel.copyTo(outInputChannel);
        } else {
            // If the window died visible, we setup a fake input channel, so that taps
            // can still detected by input monitor channel, and we can relaunch the app.
            // Create fake event receiver that simply reports all events as handled.
            mDeadWindowEventReceiver = new DeadWindowEventReceiver(mInputChannel);
        }
    }

调用WMS中的成员mInputManager

调用了WMS中的成员mInputManager来注册了InputChannel,mInputManager是一个InputManagerService。

这下就对了，事件从InputManagerService中来很合理。

    public InputChannel createInputChannel(String name) {
        return mNative.createInputChannel(name);
    }

调用的mNative的方法

这个对象是在InputManagerService创建的时候初始化的

    public InputManagerService(Context context) {
        this(new Injector(context, DisplayThread.get().getLooper()));
    }
​
    @VisibleForTesting
    InputManagerService(Injector injector) {
        // The static association map is accessed by both java and native code, so it must be
        // initialized before initializing the native service.
        mStaticAssociations = loadStaticInputPortAssociations();
​
        mContext = injector.getContext();
        mHandler = new InputManagerHandler(injector.getLooper());
        mNative = injector.getNativeService(this);
      ....
    }
//frameworks/base/services/core/java/com/android/server/input/NativeInputManagerService.java
       NativeInputManagerService getNativeService(InputManagerService service) {
            return new NativeInputManagerService.NativeImpl(service, mContext, mLooper.getQueue());
        }
​

最终返回的是一个NativeImpl实例。字面意思就知道了，这是一个Native方法的实现，createInputChannel来到了native层。

//frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
base::Result<std::unique_ptr<InputChannel>> NativeInputManager::createInputChannel(
        const std::string& name) {
    ATRACE_CALL();
    return mInputManager->getDispatcher().createInputChannel(name);
}

调用了mInputManager的getDispatcher函数看名字就知道应该有个变量mDispatcher，查看mInputManager是怎么创建的可以发现是在NativeInputManager创建的时候初始化的

    InputManager* im = new InputManager(this, this);
    mInputManager = im;

看看InputManager怎么初始化

InputManager::InputManager(
        const sp<InputReaderPolicyInterface>& readerPolicy,
        const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
    mDispatcher = createInputDispatcher(dispatcherPolicy);
    mClassifier = std::make_unique<InputClassifier>(*mDispatcher);
    mBlocker = std::make_unique<UnwantedInteractionBlocker>(*mClassifier);
    mReader = createInputReader(readerPolicy, *mBlocker);
}

这里就出现了重要的两个类InputDispatcher和InputReader,createInputChanne方法l最终调用到了InputDispatcher中的createInputChannel。

//frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
Result<std::unique_ptr<InputChannel>> InputDispatcher::createInputChannel(const std::string& name) {
    if (DEBUG_CHANNEL_CREATION) {
        ALOGD("channel '%s' ~ createInputChannel", name.c_str());
    }
    std::unique_ptr<InputChannel> serverChannel;
    std::unique_ptr<InputChannel> clientChannel;
  	//调用创建了一个serverChannel和一个clientChannel
    status_t result = InputChannel::openInputChannelPair(name, serverChannel, clientChannel);
    if (result) {
        return base::Error(result) << "Failed to open input channel pair with name " << name;
    }
    { // acquire lock
        std::scoped_lock _l(mLock);
        const sp<IBinder>& token = serverChannel->getConnectionToken();
        int fd = serverChannel->getFd();
        sp<Connection> connection =
                new Connection(std::move(serverChannel), false /*monitor*/, mIdGenerator);
        if (mConnectionsByToken.find(token) != mConnectionsByToken.end()) {
            ALOGE("Created a new connection, but the token %p is already known", token.get());
        }
        mConnectionsByToken.emplace(token, connection);
        std::function<int(int events)> callback = std::bind(&InputDispatcher::handleReceiveCallback,
                                                            this, std::placeholders::_1, token);
        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, new LooperEventCallback(callback), nullptr);
    } // release lock
    // Wake the looper because some connections have changed.
    mLooper->wake();
    return clientChannel;
}

createInputChannel干了3件事

• 首先使用openInputChannelPair创建了2个InputChannel，一个clientChannel和一个serverChannel
• 将serverChannel封装成connection，并放入成员变量mConnectionsByToken中管理，这样在事件到来的时候就可以使用connection向客户端发送事件了
• 利用Looper持续监听serverChannel，事件处理的回调消息会就到InputDispatcher::handleReceiveCallback回调，最后把clientChannel返回给客户端，也就是最初在WMS中得到的InputChannel。

首先看下openInputChannelPair

//frameworks/native/libs/input/InputTransport.cpp
status_t InputChannel::openInputChannelPair(const std::string& name,
                                            std::unique_ptr<InputChannel>& outServerChannel,
                                            std::unique_ptr<InputChannel>& outClientChannel) {
    int sockets[2];
  	//真正创建了socket
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
        status_t result = -errno;
        ALOGE("channel '%s' ~ Could not create socket pair.  errno=%s(%d)", name.c_str(),
              strerror(errno), errno);
        outServerChannel.reset();
        outClientChannel.reset();
        return result;
    }
	//设置了socket传输的大小为32k
    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));
    sp<IBinder> token = new BBinder();
    std::string serverChannelName = name + " (server)";
    android::base::unique_fd serverFd(sockets[0]);
    outServerChannel = InputChannel::create(serverChannelName, std::move(serverFd), token);
    std::string clientChannelName = name + " (client)";
    android::base::unique_fd clientFd(sockets[1]);
    outClientChannel = InputChannel::create(clientChannelName, std::move(clientFd), token);
    return OK;
}

熟悉Linux的话就知道socketpair创建了一对双向的socket，往socket[0]中写能从socket[1]读，反向也是一样，分别创建了outServerChannel和outClientChannel，两个InputChannel有着同一个BBinder作为token。

回到createInputChannel中

 const sp<IBinder>& token = serverChannel->getConnectionToken();
        int fd = serverChannel->getFd();//拿到socket fd
        sp<Connection> connection =
                new Connection(std::move(serverChannel), false /*monitor*/, mIdGenerator);
        if (mConnectionsByToken.find(token) != mConnectionsByToken.end()) {
            ALOGE("Created a new connection, but the token %p is already known", token.get());
        }
        mConnectionsByToken.emplace(token, connection);
 std::function<int(int events)> callback = std::bind(&InputDispatcher::handleReceiveCallback,
                                                            this, std::placeholders::_1, token);
        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, new LooperEventCallback(callback), nullptr);

这里将创建的serverChannel封装成了connection，同时用token作为key,存到了mConnectionsByToken中，这样就可以利用token来快速找到serverChannel封装的connection。最后监听serverChannel的fd，有事件时回调给InputDispatcher::handleReceiveCallback方法的最后把创建的clientChannel返回给了客户端，就是开头的WMS中。这样在WMS就也能通过clientChannel来获取事件了。

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