在 Camera2 API 中切换闪光灯

我的问题是，当我在不同的 Flash 模式之间切换然后想要捕获图像时，我的 captureBuilder 不会设置所选的 Flash 模式。仅当我关闭并重新打开相机时它才有效。

我拿了https://github.com/googlesamples/android-Camera2Basic作为起点。

我的方法：

   private void captureStillPicture() {
  try {
     final Activity activity = (Activity) context;
     if (null == activity || null == mCameraDevice) {
        return;
     }
     // This is the CaptureRequest.Builder that we use to take a picture.
     CaptureRequest.Builder captureBuilder =
           mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
     captureBuilder.addTarget(mImageReader.getSurface());

     // Use the same AE and AF modes as the preview.
     captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
           CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
     setCurrentFlash(captureBuilder);

     // Orientation
     int rotation = activity.getWindowManager()
           .getDefaultDisplay()
           .getRotation();
     captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));

     CameraCaptureSession.CaptureCallback captureCallback =
           new CameraCaptureSession.CaptureCallback() {

              @Override
              public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                    @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
                 super.onCaptureCompleted(session, request, result);
                 Toast.makeText(context, "image captured", Toast.LENGTH_SHORT)
                       .show();
                 unlockFocus();
              }
           };

              mCaptureSession.stopRepeating();
     mCaptureSession.capture(captureBuilder.build(), captureCallback, null);
  } catch (CameraAccessException e) {
     Log.e(this.getClass()
           .getSimpleName(), e.getMessage(), e);
  }

这是 setCurrentFlash 方法：

   private void setCurrentFlash(CaptureRequest.Builder requestBuilder) {
  if (mFlashSupported) {
     switch (flashMode.name()) {
        case FLASH_AUTO:
           requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,
                 CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
           break;
        case FLASH_ON:
           requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,
                 CaptureRequest.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
           break;
        case FLASH_OFF:
           requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
           break;
        default:
           requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,
                 CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
           break;
     }
  }

有什么想法为什么构建者在捕获之前没有正确设置闪光灯吗？

***** EDIT *****

像 Eddy Talvala 建议的那样，通过在调用 runPrecaptureSequence() 时将 flash 设置为 PreviewRequestBuilder 解决了问题

   private void runPrecaptureSequence() {
  try {
     // This is how to tell the camera to trigger.
     setCurrentFlash(previewRequestBuilder);
     previewRequestBuilder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
           CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
     // Tell #mCaptureCallback to wait for the precapture sequence to be set.
     state = STATE_WAITING_PRECAPTURE;
     captureSession.capture(previewRequestBuilder.build(), mCaptureCallback, backgroundHandler);
  } catch (CameraAccessException e) {
     e.printStackTrace();
  }

您还想在预览请求中更新 Flash 模式；通常，当您触发预捕获序列（使用 AE_PRECAPTURE_TRIGGER）时，相机设备想知道您所需的闪光模式，以便它知道是否应该打开预捕获闪光灯，从而确定最终的闪光功率。

通常的事件顺序是：

1. 将预览闪光模式设置为所需模式
2. 等待用户按下快门按钮
3. 发出带有预捕获触发器集的单个预览请求（但否则保持重复预览请求）。
4. 等待 AE_STATE_PRECAPTURE 停止成为捕获结果中的 AE 状态
5. 发出最终的捕获请求（保持相同的闪光模式）
6. 在 ImageReader 中获取最终 JPEG

（这忽略了确保焦点良好，这通常是在开始预捕获序列之前/并行完成的）