QR Code Scanning not working - ios

Question

So I have just taken over an iOS project as their first in-house dev, where previously this app had been developed by an agency.
One of the features of the app is that it needs to scan QR codes—by the look of the code the previous developers have followed this tutorial on AppCoda to implement the QR scan. Everything looks fine and I can't see anything wrong with the code yet it isn't working.
I also downloaded the completed tutorial project and that worked when I tried the QR scan. I also tried copying and pasting every single line so that it was identical to the working tutorial yet no luck.
I'm tearing my hair out trying to figure out why it isn't working.
Any help is much appreciated!
enum ScanState : Int {
case newDevice = 1
case resetDevice = 2
case replaceDevice = 3
}
class QRScannerViewController: BaseViewController,AVCaptureMetadataOutputObjectsDelegate {
#IBOutlet var scanZoneView: UIView!
#IBOutlet var scannerVIew: UIView!
#IBOutlet var scanInfoLabel: UILabel!
var capturedQR: String? = nil
var captureSession:AVCaptureSession?
var videoPreviewLayer:AVCaptureVideoPreviewLayer?
var qrCodeFrameView:UIView?
let supportedBarCodes = [AVMetadataObject.ObjectType.qr, AVMetadataObject.ObjectType.code128, AVMetadataObject.ObjectType.code39, AVMetadataObject.ObjectType.code93, AVMetadataObject.ObjectType.upce, AVMetadataObject.ObjectType.pdf417, AVMetadataObject.ObjectType.ean13, AVMetadataObject.ObjectType.aztec]
var type = "leg scan"
var device:Device?
var state:ScanState = .newDevice
override func viewDidLoad() {
super.viewDidLoad()
scanInfoLabel.text = "Scan your existing\nleg QR code"
self.navigationController?.navigationBar.dark()
//self.navigationItem.backBarButtonItem = UIBarButtonItem(title: "", style: .Plain, target: nil, action: nil)
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.navigationController?.setNavigationBarHidden(false, animated: true)
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
#if NOHARDWARE
moveToNextViewController()
#else
initiateCapture()
#endif
}
func initiateCapture() {
let captureDevice = AVCaptureDevice.default(for: AVMediaType.video)
// Get an instance of the AVCaptureDeviceInput class using the previous device object.
var error:NSError?
let input: AnyObject!
do {
input = try AVCaptureDeviceInput(device: captureDevice!) as AVCaptureDeviceInput
} catch let error1 as NSError {
error = error1
input = nil
} catch _ {
input = nil
}
if (error != nil) {
// If any error occurs, simply log the description of it and don't continue any more.
print("\(error?.localizedDescription)")
return
}
// Initialize the captureSession object.
captureSession = AVCaptureSession()
// Set the input device on the capture session.
captureSession?.addInput(input as! AVCaptureInput)
// 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 = supportedBarCodes
// 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 = scannerVIew.layer.bounds
scannerVIew.layer.addSublayer(videoPreviewLayer!)
// Start video capture.
captureSession?.startRunning()
// Initialize QR Code Frame to highlight the QR code
qrCodeFrameView = UIView()
qrCodeFrameView?.layer.borderColor = UIColor.green.cgColor
qrCodeFrameView?.layer.borderWidth = 2
scannerVIew.addSubview(qrCodeFrameView!)
scannerVIew.bringSubview(toFront: qrCodeFrameView!)
//qrCapturedLabel.text = "No QR code is detected"
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func metadataOutput(captureOutput: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], 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
return
}
// Get the metadata object.
let metadataObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject
// Here we use filter method to check if the type of metadataObj is supported
// Instead of hardcoding the AVMetadataObjectTypeQRCode, we check if the type
// can be found in the array of supported bar codes.
if supportedBarCodes.filter({ $0 == metadataObj.type }).count > 0 {
// 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 as AVMetadataMachineReadableCodeObject) as! AVMetadataMachineReadableCodeObject
let intersectionRect = barCodeObject.bounds.intersection(self.scanZoneView.frame)
if !intersectionRect.isNull &&
(intersectionRect.size.width * intersectionRect.size.height) > self.scanZoneView.bounds.width * self.scanZoneView.bounds.height / 7 {
qrCodeFrameView?.frame = barCodeObject.bounds
if process(metadataObj.stringValue!) {
captureSession?.stopRunning()
}
}
}
}
#IBAction func didTapCancel(_ sender: AnyObject) {
self.dismiss(animated: true, completion: nil)
}
}
extension QRScannerViewController {
func process(_ scanText : String) -> Bool {
var legCode : String
let codeComponents = scanText.components(separatedBy: ";")
if codeComponents.count > 0 {
legCode = codeComponents[0]
} else {
// Invalid number of parameters seperated by a ;
return false
}
// TODO Validate the LEG to LEG-XXXXX
if legCode.hasPrefix("LEG-") {
let delta: Int64 = 1 * Int64(NSEC_PER_SEC)
let time = DispatchTime.now() + Double(delta) / Double(NSEC_PER_SEC)
DispatchQueue.main.asyncAfter(deadline: time, execute: {
switch self.state {
case .resetDevice:
let realm = try! Realm()
let deviceList = realm.objects(Device.self)
let lc = legCode
self.device = deviceList.filter("legCode = %#", lc).first
if self.device == nil {
// TODO Error message: Device not associated with LEG
let vc = ErrorViewController.createErrorViewController(.DeviceNotFound)
self.present(vc, animated: true, completion: nil)
return
}
self.moveToNextViewController()
default:
self.presentingViewController?.dismiss(animated: true, completion: nil)
}
});
return true
}
return false
}
func moveToNextViewController() {
let inspectionStoryboard = UIStoryboard(name: "Impact", bundle: nil)
if let resetVC = inspectionStoryboard.instantiateViewController(withIdentifier: ImpactDetectionViewController.storyboardID) as? ImpactDetectionViewController {
resetVC.device = device
// TODO Pass the impact type across too when the G2 API is set
self.navigationController?.pushViewController(resetVC, animated: false)
}
}
#IBAction func cancelToVC(_ segue: UIStoryboardSegue) { }
}
EDIT
By not working I mean the delegate for AVCaptureMetadataOutputObjectsDelegate is never being called so it never seems to be detecting a QR code. In the AppCoda tutorial it overlays a green square where it detects the QR code but this never happens when I put that code into this app.
The camera is actually running but QR codes are never deteced.

Answer 1

Turns out the answer was deceptively (and annoyingly) simple! Of course in Swift 4 the delegates have been renamed slightly. To fix all I had to was change
func metadataOutput(captureOutput: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
to
func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {

Answer 2

You're not connecting your class to AVCaptureMetadataOutput's delegate, that's why the AVCaptureMetadataOutputObjectsDelegate functions are not being invoked. More info: https://developer.apple.com/documentation/avfoundation/avcapturemetadataoutputobjectsdelegate
Try this:
// Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
let captureMetadataOutput = AVCaptureMetadataOutput()
captureMetadataOutput.metadataObjectsDelegate = self // assign self to the delegate.
captureSession?.addOutput(captureMetadataOutput)