- (void) turnTorchOn: (bool) on {    Class captureDeviceClass = NSClassFromString(@"AVCaptureDevice");  if (captureDeviceClass != nil) {      AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];      if ([device hasTorch] && [device hasFlash]){            [device lockForConfiguration:nil];          if (on) {              [device setTorchMode:AVCaptureTorchModeOn];              [device setFlashMode:AVCaptureFlashModeOn];              torchIsOn = YES;          } else {              [device setTorchMode:AVCaptureTorchModeOff];              [device setFlashMode:AVCaptureFlashModeOff];              torchIsOn = NO;                      }          [device unlockForConfiguration];      }  }  }