Ios torchMode在开始时闪烁并立即熄灭

我不明白为什么火炬没有持续打开。
它在启动时闪烁，并立即熄灭。
我也锁定和解锁了

我添加了我的部分代码，我认为这与这里的问题有关

override func viewDidLoad() {
    super.viewDidLoad()
    initCamera()
}

func initCamera(){
    captureSession.sessionPreset = .medium

    guard let device = AVCaptureDevice.default(for: .video) else {
        print("no camera")
        return
    }
    try? device.lockForConfiguration()
    device.activeVideoMaxFrameDuration = CMTimeMake(1, 30)
    if device.hasTorch && device.isTorchAvailable && !device.isTorchActive{
        do {
            try device.setTorchModeOn(level: 1.0)
            device.torchMode = .on
        } catch {
            print("Torch could not be used")
        }
    } else {
        print("Torch is not available")
    }
    if device.isFocusModeSupported(.continuousAutoFocus){
        device.focusMode = .continuousAutoFocus
    }
    device.unlockForConfiguration()

    guard let captureInput = try? AVCaptureDeviceInput(device: device) else {return;}

    if captureSession.canAddInput(captureInput) {
        captureSession.addInput(captureInput)
    }

    let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
    view.layer.addSublayer(previewLayer)

    let videoOutput = AVCaptureVideoDataOutput()
    let queue = DispatchQueue(label: "queue image delegate", attributes: .concurrent)
    videoOutput.setSampleBufferDelegate(self, queue: queue)
    if captureSession.canAddOutput(videoOutput)
    {
        captureSession.addOutput(videoOutput)
    }
    captureSession.startRunning()
}