func scaning(){

        //获取摄像设备

        guard let device = AVCaptureDevice.default(for: .video) else { return }

        //输入流

        let input: AVCaptureDeviceInput

        do{

            input  = try AVCaptureDeviceInput.init(device: device)

        }catch{

            return

        }

        //输出流

        let output = AVCaptureMetadataOutput()

        //设置代理,并且在主线程刷新

        output.setMetadataObjectsDelegate(self, queue:DispatchQueue.main)

        output.rectOfInterest = CGRect(x: kScreenWidth/2-100, y: kScreenHeight/2-100, width: 200/kScreenWidth, height: 200/kScreenHeight)

        //初始化链接对象 / 高质量采集率

        session = AVCaptureSession()

        session.canSetSessionPreset(.high)

        if session.canAddInput(input) {

            session.addInput(input)

        }else {

            failed()

            return

        }

        if session.canAddOutput(output) {

            session.addOutput(output)

        }else {

            failed()

            return

        }

        //先添加输入输出流,后设置支持的扫码所支持的格式,不然报错

        //设置扫码支持的编码格式

        output.metadataObjectTypes = [.ean8, .ean13, .code128, .qr]

        preview = AVCaptureVideoPreviewLayer(session: session)

        preview.videoGravity = .resizeAspectFill

        preview.connection?.videoOrientation = .portrait

        preview.frame = view.bounds

        view.layer.insertSublayer(preview, at: 0)

        //开始捕捉

        session.startRunning()

    }