Я должен сканировать штрих-код / ​​QRCode, и который работает нормально, только если QRCode находится в центре экрана, а не откуда-нибудь?

Question

import AVFoundation 
import UIKit

protocol ScannerViewControllerDelegate {
    func updateVINTextField(withCode code: String);
}

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    var delegate: ScannerViewControllerDelegate?;

    override func viewDidLoad() {
        super.viewDidLoad()
        // Checking Authorization
        AVCaptureDevice.requestAccess(for: AVMediaType.video, completionHandler: { (granted :Bool) -> Void in
            if granted == true
            {
                // User granted
            }
            else
            {
                let alert = UIAlertController(title: "", message: "This app is not authorized to use Camera.", preferredStyle: .alert)

                alert.addAction(UIAlertAction(title: "Setting", style: .default, handler: { (_) in
                    DispatchQueue.main.async {
                        if let settingsURL = URL(string: UIApplication.openSettingsURLString) {
                            //UIApplication.shared.openURL(settingsURL)
                            if UIApplication.shared.canOpenURL(settingsURL) {
                                if #available(iOS 10.0, *) {
                                    UIApplication.shared.open(settingsURL, options: [:], completionHandler: nil)
                                } else {
                                    // Fallback on earlier versions
                                    UIApplication.shared.openURL(settingsURL);
                                };
                            }
                        }
                    }
                }))
                alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: { (action) in
                    self.navigationController?.popViewController(animated: true);
                }))
                //self.present(alert, animated: true, completion: nil)
                self.present(alert, animated: true, completion: {
                    self.navigationController?.popViewController(animated: true);
                })
                return
            }
        });


        view.backgroundColor = UIColor.black
        captureSession = AVCaptureSession()

        guard let videoCaptureDevice = AVCaptureDevice.default(for: .video) else { return }
        let videoInput: AVCaptureDeviceInput

        do {
            videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice)
        } catch {
            return
        }

        if (captureSession.canAddInput(videoInput)) {
            captureSession.addInput(videoInput)
        } else {
            failed()
            return
        }

        let metadataOutput = AVCaptureMetadataOutput()

        if (captureSession.canAddOutput(metadataOutput)) {
            captureSession.addOutput(metadataOutput)

            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            metadataOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.upce,
                                                  AVMetadataObject.ObjectType.code39,
                                                  AVMetadataObject.ObjectType.code39Mod43,
                                                  AVMetadataObject.ObjectType.code93,
                                                  AVMetadataObject.ObjectType.code128,
                                                  AVMetadataObject.ObjectType.ean8,
                                                  AVMetadataObject.ObjectType.ean13,
                                                  AVMetadataObject.ObjectType.aztec,
                                                  AVMetadataObject.ObjectType.pdf417,
                                                  AVMetadataObject.ObjectType.itf14,
                                                  AVMetadataObject.ObjectType.dataMatrix,
                                                  AVMetadataObject.ObjectType.interleaved2of5,
                                                  AVMetadataObject.ObjectType.qr]
        } else {
            failed()
            return
        }

        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        previewLayer.frame = view.layer.bounds
        previewLayer.videoGravity = .resizeAspectFill
        view.layer.addSublayer(previewLayer)

        captureSession.startRunning()
    }

    // If it is not able to scan the code.
    func failed()  {
        let ac = UIAlertController(title: "Scanning not supported", message: "Your device does not support scanning a code from an item. Please use a device with a camera.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
        captureSession = nil
    } 

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        if (captureSession?.isRunning == false) {
            captureSession.startRunning()
        }
        self.navigationController?.isNavigationBarHidden = false;
    }


    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        if (captureSession?.isRunning == true) {
            captureSession.stopRunning()
        }
        self.navigationController?.isNavigationBarHidden = true;
    }

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        captureSession.stopRunning()

        if let metadataObject = metadataObjects.first {
            guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
            guard let stringValue = readableObject.stringValue else { return }
            AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
            found(code: stringValue)
        }
    }

    //If The code is Successfully scanned.
    func found(code: String) {
        print(code)
        let alert = UIAlertController(title: "", message: code, preferredStyle: .alert);
        let okAction = UIAlertAction(title: "Ok", style: .default) { (action) in
            print(code);
            self.delegate?.updateVINTextField(withCode: code);
            self.navigationController?.popViewController(animated: true);
        }
        alert.addAction(okAction);
        present(alert, animated: true, completion: nil);
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}