Android应用程序键盘（Keyboard）消息处理机制分析（8）

回到Step 18中，我们继续分析EventHub.getEvent函数的实现。

在中间的for循环里面，首先会检查当前是否有输入设备被关闭，如果有，就返回一个设备移除的事件给调用方：

// 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;
    if (device->id == mFirstKeyboardId) {
        outEvent->deviceId = 0;
    } else {
        outEvent->deviceId = device->id;
    }
    outEvent->type = DEVICE_REMOVED;
    outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
    delete device;
    mNeedToSendFinishedDeviceScan = true;
    return true;
}

接着，检查当前是否有新的输入设备加入进来：

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;
    if (device->id == mFirstKeyboardId) {
        outEvent->deviceId = 0;
    } else {
        outEvent->deviceId = device->id;
    }
    outEvent->type = DEVICE_ADDED;
    outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
    mNeedToSendFinishedDeviceScan = true;
    return true;
}

        接着，再检查是否需要结束监控输入事件：

if (mNeedToSendFinishedDeviceScan) {
    mNeedToSendFinishedDeviceScan = false;
    outEvent->type = FINISHED_DEVICE_SCAN;
    outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
    return true;
}

        最后，就是要检查当前是否有还未处理的输入设备事件发生了：

// Grab the next input event.
for (;;) {
    // Consume buffered input events, if any.
    if (mInputBufferIndex < mInputBufferCount) {
        const struct input_event& iev = mInputBufferData[mInputBufferIndex++];
        const device_t* device = mDevices[mInputDeviceIndex];

        LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d", device->path.string(),
            (int) iev.time.tv_sec, (int) iev.time.tv_usec, iev.type, iev.code, iev.value);
        if (device->id == mFirstKeyboardId) {
            outEvent->deviceId = 0;
        } else {
            outEvent->deviceId = device->id;
        }
        outEvent->type = iev.type;
        outEvent->scanCode = iev.code;
        if (iev.type == EV_KEY) {
            status_t err = device->layoutMap->map(iev.code,
                & outEvent->keyCode, & outEvent->flags);
            LOGV("iev.code=%d keyCode=%d flags=0x%08x err=%d\n",
                iev.code, outEvent->keyCode, outEvent->flags, err);
            if (err != 0) {
                outEvent->keyCode = AKEYCODE_UNKNOWN;
                outEvent->flags = 0;
            }
        } else {
            outEvent->keyCode = iev.code;
        }
        outEvent->value = iev.value;

        // Use an event timestamp in the same timebase as
        // java.lang.System.nanoTime() and android.os.SystemClock.uptimeMillis()
        // as expected by the rest of the system.
        outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
        return true;
    }

    // Finish reading all events from devices identified in previous poll().
    // This code assumes that mInputDeviceIndex is initially 0 and that the
    // revents member of pollfd is initialized to 0 when the device is first added.
    // Since mFDs[0] is used for inotify, we process regular events starting at index 1.
    mInputDeviceIndex += 1;
    if (mInputDeviceIndex >= mFDCount) {
        break;
    }

    const struct pollfd& pfd = mFDs[mInputDeviceIndex];
    if (pfd.revents & POLLIN) {
        int32_t readSize = read(pfd.fd, mInputBufferData,
            sizeof(struct input_event) * INPUT_BUFFER_SIZE);
        if (readSize < 0) {
            if (errno != EAGAIN && errno != EINTR) {
                LOGW("could not get event (errno=%d)", errno);
            }
        } else if ((readSize % sizeof(struct input_event)) != 0) {
            LOGE("could not get event (wrong size: %d)", readSize);
        } else {
            mInputBufferCount = readSize / sizeof(struct input_event);
            mInputBufferIndex = 0;
        }
    }
}

        未处理的输入事件保存在成员变量mInputBufferData中，如果有的话，就可以直接返回了，否则的话，就要通过系统调用poll来等待输入设备上发生新的事件了，在我们这个场景中，就是等待键盘有键被按下或者松开了。：

int pollResult = poll(mFDs, mFDCount, -1);

 

        这里的mFDs包含了我们所要监控的输入设备的打开文件描述符，这是在前面的openPlatformInput函数中初始化的。