请教一下如何开关闪光灯

setFlash(flashMode: camera.FlashMode){ 
  if (captureSession != null){ 
    let focusModeStatus: boolean = captureSession?.isFlashModeSupported(flashMode); 
    if (focusModeStatus){ 
      captureSession.setFlashMode(flashMode); 
    } 
  } 
}