Android Input指的是输入事件，主要是触摸滑动，当然还包括类似蓝牙外设的输入。Input涉及到的主要模块
本篇主要以framework的视角来debug input问题，介绍input的资料已经很多了，所以不讲input传递流程和机制，只看如何去解决问题。
从framework的视角，首先我们要排查input driver的问题，比如从屏幕触摸输入的，那就是显示屏的input驱动；如果是蓝牙外设输入的，那就需要找BT的驱动层。
adb shell getEvent
然后再输入，看键值是否正常，如果getEvent都没有收到，就不属于framework的范畴了。
确定驱动没有问题之后，就可以通过动态或静态开启debug log。不同厂商的开关log的命令有些差异，打印log的内容也不太一样。
这里我们直接以本地debug为例，参考Android T版本的common code自己添加关键log，然后开始复现问题，检查问题时间点的log。顺便补充一下，可以通过如下命令使时间显示到秒，这样方便复现问题时对应log时间
adb shell settings put secure clock_seconds 1
/frameworks/base/core/java/android/view/ViewRootImpl.java
@UnsupportedAppUsage
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
if (event instanceof MotionEvent) {
MotionEvent me = (MotionEvent) event;
if (me.getAction() == MotionEvent.ACTION_CANCEL) {
EventLog.writeEvent(EventLogTags.VIEW_ENQUEUE_INPUT_EVENT, "Motion - Cancel",
getTitle().toString());
}
} else if (event instanceof KeyEvent) {
KeyEvent ke = (KeyEvent) event;
if (ke.isCanceled()) {
EventLog.writeEvent(EventLogTags.VIEW_ENQUEUE_INPUT_EVENT, "Key - Cancel",
getTitle().toString());
}
}
// Always enqueue the input event in order, regardless of its time stamp.
// We do this because the application or the IME may inject key events
// in response to touch events and we want to ensure that the injected keys
// are processed in the order they were received and we cannot trust that
// the time stamp of injected events are monotonic.
QueuedInputEvent last = mPendingInputEventTail;
if (last == null) {
mPendingInputEventHead = q;
mPendingInputEventTail = q;
} else {
last.mNext = q;
mPendingInputEventTail = q;
}
mPendingInputEventCount += 1;
Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
mPendingInputEventCount);
//添加log打印关键信息
Log.i(">_<!!","enqueueInputEvent: event = " + event + " ,this = " + this);
if (processImmediately) {
doProcessInputEvents();
} else {
scheduleProcessInputEvents();
}
}
这里只需要根据添加的log查看两个参数即可，event会打印出来 KeyEvent的action和keyCode，我们需要看下这里的action和keyCode是否有紊乱的情况，如果输入和get到的不对应，那还是需要driver来协调。后面打印出来的this就是此ViewRootImpl对象，具体内容可以看它的toString方法。
我们只需要在最终的log中观察这句是否打印出来，如果打印出来了，说明input事件已经成功发送到应用端了，跳过下面步骤，直接检查Step5，如果没打印这段log，再看Step2
/frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
bool InputDispatcher::dispatchKeyLocked(nsecs_t currentTime, std::shared_ptr<KeyEntry> entry,
DropReason* dropReason, nsecs_t* nextWakeupTime) {
// Preprocessing.
if (!entry->dispatchInProgress) {
// 这个是AOSP的log机制，不用再另外添加log
logOutboundKeyDetails("dispatchKey - ", *entry);
}
void InputDispatcher::logOutboundKeyDetails(const char* prefix, const KeyEntry& entry) {
//if (DEBUG_OUTBOUND_EVENT_DETAILS) {
if (true) {
ALOGD("%seventTime=%" PRId64 ", deviceId=%d, source=0x%x, displayId=%" PRId32 ", "
"policyFlags=0x%x, action=0x%x, flags=0x%x, keyCode=0x%x, scanCode=0x%x, "
"metaState=0x%x, repeatCount=%d, downTime=%" PRId64,
prefix, entry.eventTime, entry.deviceId, entry.source, entry.displayId,
entry.policyFlags, entry.action, entry.flags, entry.keyCode, entry.scanCode,
entry.metaState, entry.repeatCount, entry.downTime);
}
}
这里AOSP的log已经添加的很全面了，我们只需要手动将打印条件置为true即可。这段log中同样可以对应上action和keyCode，不过c++代码打印出来的是十六进制，但是也和上面java code中打印出来的字符串是一一对应的。如果我们最终可以搜索到这段log，说明inputDispatcher已经收到input event了，那么直接快进到Step4检查inputDispatcher状态是否正常。如果没有查看到这句log，再看Step3
/frameworks/native/services/inputflinger/reader/mapper/KeyboardInputMapper.cpp
int32_t usageCode) {
int32_t keyCode;
int32_t keyMetaState;
uint32_t policyFlags;
if (getDeviceContext().mapKey(scanCode, usageCode, mMetaState, &keyCode, &keyMetaState,
&policyFlags)) {
keyCode = AKEYCODE_UNKNOWN;
keyMetaState = mMetaState;
policyFlags = 0;
}
if (mParameters.handlesKeyRepeat) {
policyFlags |= POLICY_FLAG_DISABLE_KEY_REPEAT;
}
NotifyKeyArgs args(getContext()->getNextId(), when, readTime, getDeviceId(), mSource,
getDisplayId(), policyFlags,
down ? AKEY_EVENT_ACTION_DOWN : AKEY_EVENT_ACTION_UP,
AKEY_EVENT_FLAG_FROM_SYSTEM, keyCode, scanCode, keyMetaState, downTime);
getListener().notifyKey(&args);
ALOGI("device: %s, keyCode=%d, scanCode=%d， eventTime = %lld, action=0x%x,duwnTime=%lld",getDeviceName().c_str(), keyCode, scanCode, args,eventTime, args.action. args.downTime);
}
KeyboardInputMapper.cpp 是在Android R之后添加的工具，如果是比较旧的版本，需要在InputReader.cpp中添加log。此处可以确定input event被发送到了inputReader了，这里的值就是从getEvent读取的，如果getEvent的值是对的，但这里没有打印log，就需要打印cpp文件的callstack，看看是流程中哪一步出错。
可以通过adb命令来查看inputDispatcher的状态
adb shell dumpsys input
/frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
void InputDispatcher::dumpDispatchStateLocked(std::string& dump) {
dump += StringPrintf(INDENT "DispatchEnabled: %s\n", toString(mDispatchEnabled));
dump += StringPrintf(INDENT "DispatchFrozen: %s\n", toString(mDispatchFrozen));
dump += StringPrintf(INDENT "InputFilterEnabled: %s\n", toString(mInputFilterEnabled));
dump += StringPrintf(INDENT "FocusedDisplayId: %" PRId32 "\n", mFocusedDisplayId);
DispatcherEnabled 必须为1，并且DispatcherFrozen 必须为0，如果是inputDispatcher状态有问题，需要在代码中查看哪些地方有修改inputDispatcher的状态mDispatchEnabled，mDispatchFrozen，找到将修改状态的地方来分析问题。如果打印出来的FocusedDisplayId或FocusedApplications不符合预期，那就是display or WMS相关问题，与input流程没有关系。
/frameworks/base/core/java/android/view/View.java
public boolean dispatchKeyEvent(KeyEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onKeyEvent(event, 0);
}
Log.i(">_<!!","dispatchKeyEvent event:" + event + " to :" + v);
// Give any attached key listener a first crack at the event.
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnKeyListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnKeyListener.onKey(this, event.getKeyCode(), event)) {
//表明input被消费了
Log.i(">_<!!","Event：" + event+ " handle in: " + v
+ " ,ListenerInfo = " + li.toString());
return true;
}
if (event.dispatch(this, mAttachInfo != null
? mAttachInfo.mKeyDispatchState : null, this)) {
return true;
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return false;
}
这里的log可以表明input event正在按照view的层级依次dispatch并最终被哪个view消费，如果这个view并不是所期望的view，那么就需要查看为什么消费到这个view上面了，是layout区域有透明边界？还是期望的view并不存在，可能性就很多，细节可以再深思下。如果这里的view是符合期望的，那么问题就回到应用层了，看应用层对此input事件的响应是否有异常。
