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

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