Swfit3.0 实现扫描二维码 , 不走代理方法或者是没有扫描到数据?

Question

//  输入设备
    fileprivate lazy var input: AVCaptureDeviceInput? = {
        let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
        return try? AVCaptureDeviceInput(device: device)
    }()
    // 输出对象
    fileprivate lazy var output : AVCaptureMetadataOutput = {
        let output = AVCaptureMetadataOutput()
        output.metadataObjectTypes = output.availableMetadataObjectTypes
        output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        let centerViewFrame = self.centerView.frame
        let screenFrame = UIScreen.main.bounds
        // 测试发现系统是按照右上角作为参照, 并不是以左上角
        let x = centerViewFrame.origin.y / screenFrame.size.height
        let y = centerViewFrame.origin.x / screenFrame.size.width
        let width = centerViewFrame.size.height / screenFrame.size.height
        let height = centerViewFrame.size.width / screenFrame.size.width
        output.rectOfInterest = CGRect(x: x, y: y, width: width, height: height)
        return output
    }()
    // 会话
    fileprivate lazy var session = AVCaptureSession()
    // 预览图层
    fileprivate lazy var previewlayer: AVCaptureVideoPreviewLayer = {
        let layer = AVCaptureVideoPreviewLayer(session: self.session)
        layer?.frame = self.view.bounds
        return layer!
    }()

// MARK: - 二维码扫描
extension QRCodeViewController: AVCaptureMetadataOutputObjectsDelegate {
    fileprivate func setupScanQRCode() {
        if !session.canAddInput(input) || !session.canAddOutput(output) {
            return
        }
        session.addInput(input)
        session.addOutput(output)
        view.layer.insertSublayer(previewlayer, at: 0)
        session.startRunning()
    }
    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
        for objc in metadataObjects {
            let tempObjc = objc as! AVMetadataMachineReadableCodeObject
            CCLog(tempObjc.stringValue)
        }
    }
}

不走后面的代理方法, 如果是因为没有扫描到数据而没有走代理方法, 那这里写的有什么问题吗? 望指出