Android編程輸入事件流程詳解

本文實例講述了Android編程輸入事件流程。分享給大家供大家參考，具體如下：

EventHub對輸入設備進行了封裝。輸入設備驅動程序對用戶空間應用程序提供一些設備文件，這些設備文件放在/dev/input裡面。

EventHub掃描/dev/input下所有設備文件，並打開它們。

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對外提供了一個函數用於從輸入設備文件中讀取數據。

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;
          }
        }
      }
    }
 ...
}

對於按鍵事件，調用mDevices[i]->layoutMap->map進行映射。映射實際是由 KeyLayoutMap::map完成的，KeyLayoutMap類裡讀取配置文件qwerty.kl，由配置文件qwerty.kl決定鍵值的映射關系。你可以通過修改./development/emulator/keymaps/qwerty.kl來改變鍵值的映射關系。

JNI函數

在frameworks/base/services/jni/com_android_server_KeyInputQueue.cpp文件中，向JAVA提供了函數android_server_KeyInputQueue_readEvent，用於讀取輸入設備事件。

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調用hub->getEvent讀了取事件，然後轉換成JAVA的結構。

事件中轉線程

在frameworks/base/services/java/com/android/server/KeyInputQueue.java裡創建了一個線程，它循環的讀取事件，然後把事件放入事件隊列裡。

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);
        }
    }
  };
}

輸入事件分發線程

在frameworks/base/services/java/com/android/server/WindowManagerService.java裡創建了一個輸入事件分發線程，它負責把事件分發到相應的窗口上去。

mQueue.getEvent
dispatchKey/dispatchPointer/dispatchTrackball

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希望本文所述對大家Android程序設計有所幫助。