Android输入事件流程

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文章出处：http://www.limodev.cn/blog
作者联系方式：李先静 <xianjimli at hotmail dot com>

EventHub对输入设备进行了封装。输入设备驱动程序对用户空间应用程序提供一些设备文件，这些设备文件放在/dev/input里面。

EventHub扫描/dev/input下所有设备文件，并打开它们。

bool EventHub::openPlatformInput(void) { ... mFDCount = 1; mFDs = (pollfd *)calloc(1, sizeof(mFDs[0])); mDevices = (device_t **)calloc(1, sizeof(mDevices[0])); mFDs[0].events = POLLIN; mDevices[0] = NULL; res = scan_dir(device_path); ... return true; }

EventHub对外提供了一个函数用于从输入设备文件中读取数据。

bool EventHub::getEvent(int32_t* outDeviceId, int32_t* outType, int32_t* outScancode, int32_t* outKeycode, uint32_t *outFlags, int32_t* outValue, nsecs_t* outWhen) { ... while(1) { // First, report any devices that had last been added/removed. if (mClosingDevices != NULL) { device_t* device = mClosingDevices; LOGV("Reporting device closed: id=0x%x, name=%s/n", device->id, device->path.string()); mClosingDevices = device->next; *outDeviceId = device->id; if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0; *outType = DEVICE_REMOVED; delete device; return true; } if (mOpeningDevices != NULL) { device_t* device = mOpeningDevices; LOGV("Reporting device opened: id=0x%x, name=%s/n", device->id, device->path.string()); mOpeningDevices = device->next; *outDeviceId = device->id; if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0; *outType = DEVICE_ADDED; return true; } release_wake_lock(WAKE_LOCK_ID); pollres = poll(mFDs, mFDCount, -1); acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID); if (pollres <= 0) { if (errno != EINTR) { LOGW("select failed (errno=%d)/n", errno); usleep(100000); } continue; } for(i = 1; i < mFDCount; i++) { if(mFDs[i].revents) { LOGV("revents for %d = 0x%08x", i, mFDs[i].revents); if(mFDs[i].revents & POLLIN) { res = read(mFDs[i].fd, &iev, sizeof(iev)); if (res == sizeof(iev)) { LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d", mDevices[i]->path.string(), (int) iev.time.tv_sec, (int) iev.time.tv_usec, iev.type, iev.code, iev.value); *outDeviceId = mDevices[i]->id; if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0; *outType = iev.type; *outScancode = iev.code; if (iev.type == EV_KEY) { err = mDevices[i]->layoutMap->map(iev.code, outKeycode, outFlags); LOGV("iev.code=%d outKeycode=%d outFlags=0x%08x err=%d/n", iev.code, *outKeycode, *outFlags, err); if (err != 0) { *outKeycode = 0; *outFlags = 0; } } else { *outKeycode = iev.code; } *outValue = iev.value; *outWhen = s2ns(iev.time.tv_sec) + us2ns(iev.time.tv_usec); return true; } else { if (res<0) { LOGW("could not get event (errno=%d)", errno); } else { LOGE("could not get event (wrong size: %d)", res); } continue; } } } } ... }

对于按键事件，调用mDevices[i]->layoutMap->map进行映射。映射实际是由 KeyLayoutMap::map完成的，KeyLayoutMap类里读取配置文件qwerty.kl，由配置文件qwerty.kl决定键值的映射 关系。你可以通过修改./development/emulator/keymaps/qwerty.kl来改变键值的映射关系。

JNI函数

在frameworks/base/services/jni/com_android_server_KeyInputQueue.cpp文件 中，向JAVA提供了函数android_server_KeyInputQueue_readEvent，用于读取输入设备事件。

static jboolean android_server_KeyInputQueue_readEvent(JNIEnv* env, jobject clazz, jobject event) { gLock.lock(); sp hub = gHub; if (hub == NULL) { hub = new EventHub; gHub = hub; } gLock.unlock(); int32_t deviceId; int32_t type; int32_t scancode, keycode; uint32_t flags; int32_t value; nsecs_t when; bool res = hub->getEvent(&deviceId, &type, &scancode, &keycode, &flags, &value, &when); env->SetIntField(event, gInputOffsets.mDeviceId, (jint)deviceId); env->SetIntField(event, gInputOffsets.mType, (jint)type); env->SetIntField(event, gInputOffsets.mScancode, (jint)scancode); env->SetIntField(event, gInputOffsets.mKeycode, (jint)keycode); env->SetIntField(event, gInputOffsets.mFlags, (jint)flags); env->SetIntField(event, gInputOffsets.mValue, value); env->SetLongField(event, gInputOffsets.mWhen, (jlong)(nanoseconds_to_milliseconds(when))); return res; }

readEvent调用hub->getEvent读了取事件，然后转换成JAVA的结构。




o 事件中转线程

在frameworks/base/services/java/com/android/server/KeyInputQueue.java里创建了一个线程，它循环的读取事件，然后把事件放入事件队列里。

Thread mThread = new Thread("InputDeviceReader") { public void run() { android.os.Process.setThreadPriority( android.os.Process.THREAD_PRIORITY_URGENT_DISPLAY); try { RawInputEvent ev = new RawInputEvent(); while (true) { InputDevice di; readEvent(ev); send = preprocessEvent(di, ev); addLocked(di, curTime, ev.flags, ..., me); } } };

o 输入事件分发线程

在frameworks/base/services/java/com/android/server/WindowManagerService.java里创建了一个输入事件分发线程，它负责把事件分发到相应的窗口上去。

mQueue.getEvent
dispatchKey/dispatchPointer/dispatchTrackball