You can register a broadcast receiver to receive a callback every time the volume button is pressed, then trigger an image capture each time. You can take a look at how the CameraX sample implements this.

The broadcast receiver will look as follows. Make sure to register and unregister it appropriately.

private val volumeDownReceiver = object : BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        when (intent.getIntExtra(KEY_EVENT_EXTRA, KeyEvent.KEYCODE_UNKNOWN)) {
            KeyEvent.KEYCODE_VOLUME_DOWN -> // Trigger an image capture
        }
    }
}

Since -it seems- you’re using CameraX’s CameraView API, you can trigger an image capture by calling one of its takePicture methods.

• takepicture(Executor, OnImageCaptureCallback)
• takePicture(OutputFileOptions, Executor, OnImageSavedCallback)

The image capture should only occur after the camera has been set up.

I’m trying to make an app take a picture when the volume buttons are pressed, like snapchat and the like do. This app is using the CamaraX Library for camera functionality. Now as far as I can tell the CameraXView should let me set an onKeyListener as it extends frameLayout -> ViewGroup -> View. However, everything I’ve tried so far does not pick up the KeyEvents.

public class CameraXFragment extends LoggingFragment implements CameraFragment {
  ...
  private CameraXView          camera;
  ...
  private void initControls() {
    ...
    // This doesn't work
    camera.setOnKeyListener((v, keyCode, event) -> {
      Log.e(TAG, "KeyEvent please: " + keyCode);
      return false;
    });
    ...
    // This does work
    camera.setOnTouchListener((v, event) -> gestureDetector.onTouchEvent(event));
  }
}

CameraXView does have a onTouchEvent so I tried adding a onKeyDown within it as well but that doesn’t seem to have worked.

The camera.setOnTouchEventLister was not added by me so I don’t fully understand why that is working but mine isn’t.