code: public synchronized void stopPreview() {
      if (autoFocusManager != null) {
        autoFocusManager.stop();
        autoFocusManager = null;
      }
      if (camera != null && previewing) {
        camera.stopPreview();
        previewCallback.setHandler(null, 0);
        previewing = false;
      }
    }
docs: Tells the camera to stop drawing preview frames.