iOS条形码扫描仪应用程序崩溃，没有崩溃日志

我正在尝试制作一个条形码扫描仪应用程序。一旦摄像头会话开始，应用程序就会在几秒钟内崩溃

我找不到这背后的原因。还有，如何解决这个问题

我曾经做过barcde扫描仪

import Foundation
import UIKit
import AVFoundation
import CoreData
enum BarcodeScanError : String{
    case cameraLoadFailed = "Camera Load Failed"
    case NoValidBarcode = "No Valid Barcode"
    
}

class ScanBoardingPassViewController : UIViewController {


//MARK: - Properties
var viewModel : ScanBoardingPassViewModel? = nil
var captureSession : AVCaptureSession?
var videoPreviewLayer: AVCaptureVideoPreviewLayer?
var qrCodeFrameView: UIView?


private let supportedCodeTypes = [AVMetadataObject.ObjectType.aztec,
                                 AVMetadataObject.ObjectType.pdf417]

//MARK: - Outlets
@IBOutlet weak var btnCancel: UIButton!

//MARK: - View Life Cycle
override func viewDidLoad() {
    viewModel = ScanBoardingPassViewModel()
    self.captureSession = AVCaptureSession()
    self.setUpView()
    super.viewDidLoad()
    
}

override func viewWillDisappear(_ animated: Bool) {

    super.viewWillDisappear(true)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

//MARK: - Set Up View
func setUpView() {
            self.setUpBarCodeScanner()
    self.view.bringSubviewToFront(self.btnCancel)

            self.setUpBarcodeRecognizerFrame()
}

private func setUpBarCodeScanner() {
    // Get the back-facing camera for capturing videos
    guard let captureDevice = AVCaptureDevice.default(for: AVMediaType.video) else {
        debugPrint(BarcodeScanError.cameraLoadFailed)
        return
    }
    
    do {
        // Get an instance of the AVCaptureDeviceInput class using the previous device object.
        let input = try AVCaptureDeviceInput(device: captureDevice)
        
        // Set the input device on the capture session.
        captureSession?.addInput(input)
        
        // Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
        let captureMetadataOutput = AVCaptureMetadataOutput()
        captureSession?.addOutput(captureMetadataOutput)
        
        // Set delegate and use the default dispatch queue to execute the call back
        captureMetadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        captureMetadataOutput.metadataObjectTypes = supportedCodeTypes
        //            captureMetadataOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.qr]
        
    } catch {
        // If any error occurs, simply print it out and don't continue any more.
        print(error)
        return
    }
    
    // Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
    videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
    videoPreviewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
    videoPreviewLayer?.frame = view.layer.bounds
    view.layer.addSublayer(videoPreviewLayer!)
    
    // Start video capture.
    captureSession?.startRunning()
}

private func setUpBarcodeRecognizerFrame() {
    // Initialize QR Code Frame to highlight the QR code
    qrCodeFrameView = UIView()
    
    if let qrCodeFrameView = qrCodeFrameView {
        qrCodeFrameView.layer.borderColor = UIColor.green.cgColor
        qrCodeFrameView.layer.borderWidth = 2
        view.addSubview(qrCodeFrameView)
        view.bringSubviewToFront(qrCodeFrameView)
    }
}


//MARK: - Outlets
@IBAction func btnCancelPressed(_ sender: UIButton) {
    self.dismissView()
    
}

    func dismissView() {
        self.dismiss(animated: true, completion: nil)
    }
    
}

extension ScanBoardingPassViewController: AVCaptureMetadataOutputObjectsDelegate {


func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
    // Check if the metadataObjects array is not nil and it contains at least one object.
    if metadataObjects.count == 0 {
        qrCodeFrameView?.frame = CGRect.zero
        debugPrint(BarcodeScanError.NoValidBarcode)
        return
    }
    
    // Get the metadata object.
    let metadataObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject
    
    if supportedCodeTypes.contains(metadataObj.type) {
        // If the found metadata is equal to the QR code metadata (or barcode) then update the status label's text and set the bounds
        let barCodeObject = videoPreviewLayer?.transformedMetadataObject(for: metadataObj)
        qrCodeFrameView?.frame = barCodeObject!.bounds
        
        
        if metadataObj.stringValue != nil {
            captureSession?.stopRunning()
            
            debugPrint("Valid Barcode found \(metadataObj.stringValue!)")
        if let boardingPass = viewModel?.parseBoardingPassString(boardingPassString : metadataObj.stringValue!) {
           

                let unitOfWork = UnitOfWork(context:( UIApplication.shared.delegate as! AppDelegate).persistentContainer.newBackgroundContext() )

                unitOfWork.boardingPassRepository.saveBoardingPasses(boardingPass: boardingPass)
                unitOfWork.saveChanges()
                print(unitOfWork.boardingPassRepository.getBoardingPasses(predicate: nil))
                self.dismissView()


               }
            }
        }
    }
   }

---

照相机没有被击中。但是，应用程序每次都会在几秒钟内发出一个lldb。

为什么要将对super.viewDidLoad的调用放在viewDidLoad方法的末尾？虽然这段代码可能提供了一个问题的解决方案，但最好添加上下文来说明为什么/如何工作。这可以帮助未来的用户学习，并将这些知识应用到他们自己的代码中。在解释代码时，用户可能会以投票的形式向您提供正面反馈。

//  Created by Satya Narayana on 17/11/20.
//

import UIKit
import AVFoundation
import UIKit

class QRViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    //MARK: Outlets
    @IBOutlet weak var qrLbl: UILabel! // BarCode displaying Label
    @IBOutlet weak var sView: UIView!  // View
    
    //MARK: Variables
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    
    
    //MARK: View Methods
    override func viewDidLoad() {
        super.viewDidLoad()

        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 = [.qr, .ean13, .code128]
        } else {
            failed()
            return
        }

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

        captureSession.startRunning()
    }
   
    
 
    
    
    func failed() {
        self.showToast(message: "Scanning not supported.Your device does not support scanning a code from an item. Please use a device with a camera.", seconds: 1.0)
        captureSession = nil
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        qrLbl.isHidden = true
        if (captureSession?.isRunning == false) {
            captureSession.startRunning()
        }
    }

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

        if (captureSession?.isRunning == true) {
            captureSession.stopRunning()
        }
    }

    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)
        }
        dismiss(animated: true)
    }

    //MARK:- Found BARCODE
    func found(code: String) {
        print(code)
        if code != ""{
        print(code) // This is Barcode
            qrLbl.text = code
        }else{
         // if you need run again uncomment below line
           //self.captureSession.startRunning()
                

        }
    }


    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}