code: public synchronized void requestPreviewFrame(Handler handler, int message) {
      OpenCamera theCamera = camera;
      if (theCamera != null && previewing) {
        previewCallback.setHandler(handler, message);
        theCamera.getCamera().setOneShotPreviewCallback(previewCallback);
      }
    }
docs: A single preview frame will be returned to the handler supplied. The data will arrive as byte[]
  in the message.obj field, with width and height encoded as message.arg1 and message.arg2,
  respectively.
  
  @param handler The handler to send the message to.
  @param message The what field of the message to be sent.