QR Code Scanner won't work in Swift 4

Question

I've tried following and downloading this QR Code Scanner sample project by Simon Ng, https://www.appcoda.com/barcode-reader-swift/ However, when I try to simulate the sample project to my iPhone, the camera doesn't work. The camera privacy alert doesn't appear and the screen is just white. I've already enabled NSCamera privacy in Info.plist but it doesn't seem to do the job.

QRScannerController.

import UIKit
import AVFoundation

class QRScannerController: UIViewController {

    @IBOutlet var messageLabel:UILabel!
    @IBOutlet var topbar: UIView!

    var captureSession = AVCaptureSession()

    var videoPreviewLayer: AVCaptureVideoPreviewLayer?
    var qrCodeFrameView: UIView?

    private let supportedCodeTypes = [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]

    override func viewDidLoad() {
        super.viewDidLoad()

        // Get the back-facing camera for capturing videos
        let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDualCamera], mediaType: AVMediaType.video, position: .back)

        guard let captureDevice = deviceDiscoverySession.devices.first else {
            print("Failed to get the camera device")
            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()

        // Move the message label and top bar to the front
        view.bringSubview(toFront: messageLabel)
        view.bringSubview(toFront: topbar)

        // 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.bringSubview(toFront: qrCodeFrameView)
        }
    }

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

    // MARK: - Helper methods

    func launchApp(decodedURL: String) {

        if presentedViewController != nil {
            return
        }

        let alertPrompt = UIAlertController(title: "Open App", message: "You're going to open \(decodedURL)", preferredStyle: .actionSheet)
        let confirmAction = UIAlertAction(title: "Confirm", style: UIAlertActionStyle.default, handler: { (action) -> Void in

            if let url = URL(string: decodedURL) {
                if UIApplication.shared.canOpenURL(url) {
                    UIApplication.shared.open(url, options: [:], completionHandler: nil)
                }
            }
        })

        let cancelAction = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: nil)

        alertPrompt.addAction(confirmAction)
        alertPrompt.addAction(cancelAction)

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

}

extension QRScannerController: 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
            messageLabel.text = "No QR code is detected"
            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 {
                launchApp(decodedURL: metadataObj.stringValue!)
                messageLabel.text = metadataObj.stringValue
            }
        }
    }

}

score 2 · Answer 1 · answered Feb 02 '18 at 06:55

Before start capturing check whether the camera permission is granted or not. If it's not granted ask permission after getting authorization start capture. for reference use below code snippet

import UIKit
import AVFoundation


class QRScannerVC: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    @IBOutlet weak var qrCodeView:UIView!

    var backBtn:UIBarButtonItem!

    var captureSession:AVCaptureSession?
    var videoPreviewLayer:AVCaptureVideoPreviewLayer?
    var qrCodeFrameView:UIView?

    let supportedCodeTypes = [AVMetadataObjectTypeUPCECode,
                              AVMetadataObjectTypeCode39Code,
                              AVMetadataObjectTypeCode39Mod43Code,
                              AVMetadataObjectTypeCode93Code,
                              AVMetadataObjectTypeCode128Code,
                              AVMetadataObjectTypeEAN8Code,
                              AVMetadataObjectTypeEAN13Code,
                              AVMetadataObjectTypeAztecCode,
                              AVMetadataObjectTypePDF417Code,
                              AVMetadataObjectTypeQRCode]

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

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

        self.askPermission()
    }




    func askPermission() {
        let cameraMediaType = AVMediaTypeVideo
        let cameraAuthorizationStatus = AVCaptureDevice.authorizationStatus(forMediaType: cameraMediaType)

        switch cameraAuthorizationStatus {
        case .authorized:
            self.startVideoCapture()
            break
        case .restricted,.denied,.notDetermined:
            AVCaptureDevice.requestAccess(forMediaType: AVMediaTypeVideo) { granted in
                if !granted {
                    let alert = ViewUtils.getDialog(title: "Allow App access to your Camera", message: "App need access to Camera to scan QR code")
                    alert.addAction(UIAlertAction(title: "Allow Access", style: .default) { action in
                        if let url = NSURL(string:UIApplicationOpenSettingsURLString) {
                            UIApplication.shared.openURL(url as URL)
                        }
                    })
                    alert.addAction(UIAlertAction(title: "Not Now", style: .default) { action in
                    })
                    self.present(alert, animated: true, completion: nil)
                }
                else{
                    self.startVideoCapture()
                }
            }
        default: break
        }
    }

    func startVideoCapture(){
        // Get an instance of the AVCaptureDevice class to initialize a device object and provide the video as the media type parameter.
        let captureDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)

        do {
            // Get an instance of the AVCaptureDeviceInput class using the previous device object.
            let input = try AVCaptureDeviceInput(device: captureDevice)

            // Initialize the captureSession object.
            captureSession = AVCaptureSession()

            // 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

            // Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
            videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
            videoPreviewLayer?.frame = self.qrCodeView.bounds
            self.qrCodeView.layer.addSublayer(videoPreviewLayer!)
            self.qrCodeView.clipsToBounds = true
            // Start video capture.
            captureSession?.startRunning()
            qrCodeFrameView = UIView()

            if let qrCodeFrameView = qrCodeFrameView {
                qrCodeFrameView.layer.borderColor = UIColor.green.cgColor
                qrCodeFrameView.layer.borderWidth = 2
                self.qrCodeView.addSubview(qrCodeFrameView)
                self.qrCodeView.bringSubview(toFront: qrCodeFrameView)
            }

        } catch {
            // If any error occurs, simply print it out and don't continue any more.
            print(error)
            return
        }
    }

    // MARK: - AVCaptureMetadataOutputObjectsDelegate Methods

    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {

        // Check if the metadataObjects array is not nil and it contains at least one object.
        if metadataObjects == nil || metadataObjects.count == 0 {
            qrCodeFrameView?.frame = CGRect.zero
            print("No QR/barcode is detected")
            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 then update the status label's text and set the bounds
            let barCodeObject = videoPreviewLayer?.transformedMetadataObject(for: metadataObj)
            if barCodeObject != nil{
                qrCodeFrameView?.frame = barCodeObject!.bounds
            }

            if metadataObj.stringValue != nil {
                print("\(metadataObj.stringValue)")
                if metadataObj.stringValue! != ""{

                }
            }
        }
    }
}

Hope this will help you

I tried using ur code but an error occured saying "Use of unresolved identifier 'ViewUtils'". Anyway i can fix this? — Kinja, Feb 04 '18 at 11:10
That is custom dialog which i have created as a extension instead of you can use UIAlertController — Ganesh Manickam, Feb 04 '18 at 14:47

QR Code Scanner won't work in Swift 4

1 Answers1