Switching front/back camera not work on iOS

Question

I have tried to switch camera type, like on document.

But this is not work.

I think camera switch is not complete, but call OpenAndStart()

How do I know if camera switch is complete and can start?

private CameraDeviceBehaviour _cameraDeviceBehaviour;
private void Switch(){
     _cameraDeviceBehaviour.Close();
     _cameraDeviceBehaviour.CameraDeviceType = CameraDeviceBaseBehaviour.DeviceType.Back;
     _cameraDeviceBehaviour.OpenAndStart();
}

Thank you.