android：相机未拍照

Question

The idea is simple: My App should create a camera object, show a preview and take a picture (without pressing any button) and close the camera afterwards. Unfortunately it is not even taking any pictures. (Means: My callback code which should be executed after the picture is taken is never reached.)

I'm using a little wrapper class for the android camera api. My activity code looks like this:

camera = new SurveillanceCamera(this, layoutForPreview);
camera.start();
camera.takePicture();

The wrapper class:

public SurveillanceCamera(Context context, LinearLayout previewLayout) {
    cameraInstance = Camera.open(findBackFacingCamera());
    pictureCallback = getPictureCallback();
    cameraPreview = new CameraPreview(context, cameraInstance);
    this.previewLayout = previewLayout;
    this.previewLayout.addView(cameraPreview);
    cameraInstance.startPreview();
  }

  public void takePicture() {
    //this code is reached
    cameraInstance.takePicture(null, null, pictureCallback);
  }

  public void start() {
    if (cameraInstance == null) {
      cameraInstance = Camera.open(findBackFacingCamera());
      pictureCallback = getPictureCallback();
      cameraPreview.setCamera(cameraInstance);
      cameraInstance.startPreview();
    }
  }

  private PictureCallback getPictureCallback() {
    PictureCallback picture = new PictureCallback() {
      @Override
      public void onPictureTaken(byte[] data, Camera camera) {
        Log.e(TAG, "Jey picture was taken...");
        // refresh camera to continue preview
        cameraPreview.refreshCamera(cameraInstance);
      }
    };
    return picture;
  }

  private int findBackFacingCamera() {
    int cameraId = -1;
    // Search for the back facing camera
    // get the number of cameras
    int numberOfCameras = Camera.getNumberOfCameras();
    // for every camera check
    for (int i = 0; i < numberOfCameras; i++) {
      CameraInfo info = new CameraInfo();
      Camera.getCameraInfo(i, info);
      if (info.facing == CameraInfo.CAMERA_FACING_BACK) {
        cameraId = i;
        break;
      }
    }
    return cameraId;
  }

There are no exceptions thrown in the code, but the Log.e() in onPictureTaken is not shown. It seems that the camera preview is displayed but nothing happens. Is it possible, that the preview is not fully loaded at the moment when camera.takePicture() is executed? Any suggestions?

Answer 1

Your suspicion is most likely justified. I don't see when setPreviewDisplay() is called. But this call should complete for takePicture() to succeed.

It is impossible to simply call

camera = new SurveillanceCamera(this, layoutForPreview);
camera.start();
camera.takePicture();

because to complete a setPreviewDisplay() call, you need a fully initialized Holder instance, but you only add the surface view in constructor.

It would be best to register a SurfaceHolder.Callback and call takePicture() from the surfaceChanged() callback.