InputManagerService 十分钟让你了解Android触摸事件原理( 三 ) _Android

void InputDispatcher::setInputWindows(const Vector<sp<InputWindowHandle> >& inputWindowHandles) { ... mWindowHandles = inputWindowHandles; ...谁会调用这个函数呢？真正的入口是WindowManagerService中的InputMonitor会简介调用InputDispatcher::setInputWindows ，这个时机主要是跟窗口增改删除等逻辑相关，以addWindow为例：

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从上面流程可以理解为什么说WindowManagerService跟InputManagerService是相辅相成的了，到这里，如何找到目标窗口已经解决了，下面就是如何将事件发送到目标窗口的问题了。
如何将事件发送到目标窗口找到了目标窗口，同时也将事件封装好了，剩下的就是通知目标窗口，可是有个最明显的问题就是，目前所有的逻辑都是在SystemServer进程，而要通知的窗口位于APP端的用户进程，那么如何通知呢？下意识的可能会想到Binder通信，毕竟Binder在Android中是使用最多的IPC手段了，不过Input事件处理这采用的却不是Binder：高版本的采用的都是Socket的通信方式，而比较旧的版本采用的是Pipe管道的方式。
void InputDispatcher::dispatchEventLocked(nsecs_t currentTime, EventEntry* eventEntry, const Vector<InputTarget>& inputTargets) { pokeUserActivityLocked(eventEntry); for (size_t i = 0; i < inputTargets.size(); i++) { const InputTarget& inputTarget = inputTargets.itemAt(i); ssize_t connectionIndex = getConnectionIndexLocked(inputTarget.inputChannel); if (connectionIndex >= 0) { sp<Connection> connection = mConnectionsByFd.valueAt(connectionIndex); preparedispatchCycleLocked(currentTime, connection, eventEntry, &inputTarget); } else { } }}代码逐层往下看会发现最后会调用到InputChannel的sendMessage函数，最会通过socket发送到APP端（Socket怎么来的接下来会分析），

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这个Socket是怎么来的呢？或者说两端通信的一对Socket是怎么来的呢？其实还是要牵扯到WindowManagerService ，在APP端向WMS请求添加窗口的时候，会伴随着Input通道的创建，窗口的添加一定会调用ViewRootImpl的setView函数：
ViewRootImpl
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) { ... requestLayout(); if ((mWindowAttributes.inputFeatures & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {  mInputChannel = new InputChannel(); } try { mOrigWindowType = mWindowAttributes.type; mAttachInfo.mRecomputeGlobalAttributes = true; collectViewAttributes();  res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes, getHostVisibility(), mDisplay.getDisplayId(), mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mAttachInfo.mOutsets, mInputChannel); }...  if (mInputChannel != null) { if (mInputQueueCallback != null) { mInputQueue = new InputQueue(); mInputQueueCallback.onInputQueueCreated(mInputQueue); } mInputEventReceiver = new WindowInputEventReceiver(mInputChannel, Looper.myLooper()); }在IWindowSession.aidl定义中 InputChannel是out类型，也就是说需要服务端进行填充，那么接着看服务端WMS如何填充的呢？
public int addWindow(Session session, IWindow client, int seq, WindowManager.LayoutParams attrs, int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets, Rect outOutsets, InputChannel outInputChannel) {... if (outInputChannel != null && (attrs.inputFeatures & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) { String name = win.makeInputChannelName();  InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);  win.setInputChannel(inputChannels[0]);  inputChannels[1].transferTo(outInputChannel);  mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle); }WMS首先创建socketpair作为全双工通道，并分别填充到Client与Server的InputChannel中去；之后让InputManager将Input通信信道与当前的窗口ID绑定，这样就能知道哪个窗口用哪个信道通信了；最后通过Binder将outInputChannel回传到APP端，下面是SocketPair的创建代码：
status_t InputChannel::openInputChannelPair(const String8& name, sp<InputChannel>& outServerChannel, sp<InputChannel>& outClientChannel) { int sockets[2]; if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) { status_t result = -errno; ... 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)"); outServerChannel = new InputChannel(serverChannelName, sockets[0]);  String8 clientChannelName = name; clientChannelName.append(" (client)"); outClientChannel = new InputChannel(clientChannelName, sockets[1]); return OK;}