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。
本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/966621，如需转载请自行联系原作者
