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.cpp
status_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server
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);
return OK;
}