既然事件最终是通过 InputChannel 发送出去，那么我们继续追踪 InputChannel。在 InputManagerService 中 registerInputChannel
public void registerInputChannel(InputChannel inputChannel,
InputWindowHandle inputWindowHandle) {
if (inputChannel == null) {
throw new IllegalArgumentException("inputChannel must not be null.");
}
nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);
}
nativeRegisterInputManager
static void nativeRegisterInputChannel(JNIEnv* env, jclass /* clazz */,
jlong ptr, jobject inputChannelObj, jobject inputWindowHandleObj, jboolean monitor) {
NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);
sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
if (inputChannel == NULL) {
throwInputChannelNotInitialized(env);
return;
}
sp<InputWindowHandle> inputWindowHandle =
android_server_InputWindowHandle_getHandle(env, inputWindowHandleObj);
status_t status = im->registerInputChannel(
env, inputChannel, inputWindowHandle, monitor);
if (status) {
String8 message;
message.appendFormat("Failed to register input channel. status=%d", status);
jniThrowRuntimeException(env, message.string());
return;
}
if (! monitor) {
android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
handleInputChannelDisposed, im);
}
}
NativeInputManager的registerInputChannel还会调用到 InputDispatcher 的 registerInputChannel，会通过InputChannel创建相应的 Connection ，同时将InputChannel加入到 InputManager 中。上面的 InputChannel 获取
status_t InputDispatcher::registerInputChannel(const sp<InputChannel>& inputChannel,
const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {
{ // acquire lock
AutoMutex _l(mLock);
if (getConnectionIndexLocked(inputChannel) >= 0) {
ALOGW("Attempted to register already registered input channel '%s'",
inputChannel->getName().string());
return BAD_VALUE;
}
sp<Connection> connection = new Connection(inputChannel, inputWindowHandle, monitor);
int fd = inputChannel->getFd();
mConnectionsByFd.add(fd, connection);
if (monitor) {
mMonitoringChannels.push(inputChannel);
}
mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
} // release lock
// Wake the looper because some connections have changed.
mLooper->wake();
return OK;
}
对于InputReaderThread和InputDispatcherThread是运行在SystemServer进程中的，而我们的应用进程是和其不在同一个进程中的。这之间一定也是有进程间的通信机制在里面。即 ViewRootImpl 的 setView 方法中
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
....
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
....
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
....
}
WMS的 addWindow 方法
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
InputChannel outInputChannel) {
....
final boolean openInputChannels = (outInputChannel != null
&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
if (openInputChannels) {
win.openInputChannel(outInputChannel);
}
....
}
void openInputChannel(InputChannel outInputChannel) {
if (mInputChannel != null) {
throw new IllegalStateException("Window already has an input channel.");
}
String name = makeInputChannelName();
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 {
mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
}
mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);
}
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;
ALOGE("channel '%s' ~ Could not create socket pair. errno=%d",
name.string(), errno);
outServerChannel.clear();
outClientChannel.clear();
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;
}
这里创建两个 Socket，设置为读写双端，然后根据 socket，创建出连两个InputChannel，一个 Server，一个Client。这样在SystemServer进程和应用进程间的InputChannel的通信就可以连接，由于两个channel不在同一个进程中，这里进程通信则是通过socket来进行。在sendMessage和receiveMessage中，通过对Socket的写，读操作来实现消息的传递。
status_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);
if (nWrite < 0) {
int error = errno;
if (error == EAGAIN || error == EWOULDBLOCK) {
return WOULD_BLOCK;
}
if (error == EPIPE || error == ENOTCONN || error == ECONNREFUSED || error == ECONNRESET) {
return DEAD_OBJECT;
}
return -error;
}
if (size_t(nWrite) != msgLength) {
return DEAD_OBJECT;
}
return OK;
}
status_t InputChannel::receiveMessage(InputMessage* msg) {
ssize_t nRead;
do {
nRead = ::recv(mFd, msg, sizeof(InputMessage), MSG_DONTWAIT);
} while (nRead == -1 && errno == EINTR);
if (nRead < 0) {
int error = errno;
if (error == EAGAIN || error == EWOULDBLOCK) {
return WOULD_BLOCK;
}
if (error == EPIPE || error == ENOTCONN || error == ECONNREFUSED) {
return DEAD_OBJECT;
}
return -error;
}
if (nRead == 0) { // check for EOF
return DEAD_OBJECT;
}
if (!msg->isValid(nRead)) {
return BAD_VALUE;
}
return OK;
}
这样，WindowInputEventReceiver 便可以接收输入事件
下面来分析一下 InputEventReceiver 中的 nativeInit 方法
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
jobject inputChannelObj, jobject messageQueueObj) {
....
sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,
receiverWeak, inputChannel, messageQueue);
status_t status = receiver->initialize();
.....
}
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);
}
}
}
int ALooper_addFd(ALooper* looper, int fd, int ident, int events,
ALooper_callbackFunc callback, void* data) {
return ALooper_to_Looper(looper)->addFd(fd, ident, events, callback, data);
}
int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
Request request;
request.fd = fd;
request.ident = ident;
request.events = events;
request.seq = mNextRequestSeq++;
request.callback = callback;
request.data = data;
if (mNextRequestSeq == -1) mNextRequestSeq = 0;
struct epoll_event eventItem;
request.initEventItem(&eventItem);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
if (epollResult < 0) {
return -1;
}
mRequests.add(fd, request);
}
}
addFd就是对传递的fd 添加 epoll 监控，Looper 会循环调用 pollOnce，而pollOnce方法的核心实现就是pollInner 。其代码大致实现内容为等待消息的到来，当有消息到来后，根据消息类型做一些判断处理，然后调用其相关的callback。我们当前是对于开启的socket的一个监听，当有数据到来，我们便会执行相应的回调。这里对于InputChannel的回调是在调用了NativeInputEventReceiver的handleEvent方法。
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {
.....
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;
}
....
return 1;
}
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,
bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {
...
for(;;) {
...
InputEvent* inputEvent;
status_t status = mInputConsumer.consume(&mInputEventFactory,
consumeBatches, frameTime, &seq, &inputEvent);
...
}
...
}
status_t InputConsumer::consume(InputEventFactoryInterface* factory,
bool consumeBatches, nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent) {
while (!*outEvent) {
....
status_t result = mChannel->receiveMessage(&mMsg);
....
}
}
调用consume方法会持续的调用InputChannel的receiveMessage方法来从socket中读取数据。到这里，我们已经将写入socket的事件读出来了。接下来就会通过 ViewRootImpl 将事件派发到 Activity 中去。
事件派发原理图
总结
在SystemServer进程通过epoll 监听input，在用户进程创建window的时候注册channel，channel通过socket进行进程间通信，InputConsumer 通过consume 发送到用户activity消费输入事件
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