QR扫描仪挂起时，我无法正确扫描QR码

Question

当我尝试使用qr库扫描qr代码并运行视图控制器时，它可以工作3秒钟，然后挂起，但是在其他应用程序中实现相同功能时，效果很好

import UIKit
import AVFoundation
import QRCodeReader

class QRScannerViewController: UIViewController , QRCodeReaderViewControllerDelegate{
    // Good practice: create the reader lazily to avoid cpu overload during the
    // initialization and each time we need to scan a QRCode
    lazy var readerVC: QRCodeReaderViewController = {
        let builder = QRCodeReaderViewControllerBuilder {
            $0.reader = QRCodeReader(metadataObjectTypes: [.qr], captureDevicePosition: .back)

            // Configure the view controller (optional)
            $0.showTorchButton        = false
            $0.showSwitchCameraButton = false
            $0.showCancelButton       = true
            $0.showOverlayView        = true
            $0.rectOfInterest         = CGRect(x: 0.2, y: 0.2, width: 0.6, height: 0.6)
        }

        return QRCodeReaderViewController(builder: builder)
    }()

    @IBAction func scanAction(_ sender: AnyObject) {
        // Retrieve the QRCode content
        // By using the delegate pattern
        readerVC.delegate = self

        // Or by using the closure pattern
        readerVC.completionBlock = { (result: QRCodeReaderResult?) in
            print(result)
        }

        // Presents the readerVC as modal form sheet
        readerVC.modalPresentationStyle = .formSheet

        present(readerVC, animated: true, completion: nil)
    }

    // MARK: - QRCodeReaderViewController Delegate Methods

    public func reader(_ reader: QRCodeReaderViewController, didScanResult result: QRCodeReaderResult) {
        reader.stopScanning()

        dismiss(animated: true, completion: nil)
    }

    //This is an optional delegate method, that allows you to be notified when the user switches the cameraName
    //By pressing on the switch camera button
    public func reader(_ reader: QRCodeReaderViewController, didSwitchCamera newCaptureDevice: AVCaptureDeviceInput) {

        //        if let cameraName = newCaptureDevice.device.localizedName as? String{
        //            print("Switching capture to: \(cameraName)")
        //        } else {
        //            return
        //        }

    }

    public func readerDidCancel(_ reader: QRCodeReaderViewController) {
        reader.stopScanning()

        dismiss(animated: true, completion: nil)
    }

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

}