QR Scanner

QRScanningViewController.swift

import Foundation
import AVFoundation
import UIKit

//MARK:- UIViewController
class QRScanningViewController: UIViewController {
    
    @IBOutlet weak var previewView: PreviewView!
    let qrScanner:QRScanner = QRScanner()

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        qrScanner.previewView = previewView
        qrScanner.delegate = self
        previewView.videoPreviewLayer.videoGravity = .resizeAspectFill
        qrScanner.session.startRunning()
    }
}

extension QRScanningViewController: QRScannerDelegate {
    func scannerDetected(item:Any) {
        DispatchQueue.main.async {[weak self] in
            guard let message = item as? String else { return }
            let alert = UIAlertController.init(title: "Scanned", message: message, preferredStyle: .alert)
            let confirmAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
            alert.addAction(confirmAction)
            self?.present(alert, animated: true)
        }
    }
}

//MARK:- QR Scanner
protocol QRScannerDelegate: class {
    func scannerDetected(item:Any)
}

class QRScanner: NSObject {
    
    let session  = AVCaptureSession()
    let qrScanQueue = DispatchQueue(label: "com.myApp.qrScanQueue")
    weak var delegate:QRScannerDelegate?
    
    weak var previewView:PreviewView? {
        didSet {
            previewView?.videoPreviewLayer.session = session
        }
    }
    
    override init() {
        super.init()
        
        guard
            let videoDevice = AVCaptureDevice.default(for: .video),
            let deviceInput = try? AVCaptureDeviceInput(device: videoDevice)
            else { return }
        
        session.addInput(deviceInput)
        
        let dataOutput = AVCaptureMetadataOutput()
        session.addOutput(dataOutput)
        dataOutput.metadataObjectTypes = [.qr]
        dataOutput.setMetadataObjectsDelegate(self, queue: qrScanQueue)
    }
}

extension QRScanner: AVCaptureMetadataOutputObjectsDelegate {
    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        guard
            let readableCode = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
            let readableString = readableCode.stringValue
            else { return }
        delegate?.scannerDetected(item: readableString)
    }
}

//MARK:- Preview View
class PreviewView: UIView {
    override class var layerClass: AnyClass {
        return AVCaptureVideoPreviewLayer.self
    }
    var videoPreviewLayer: AVCaptureVideoPreviewLayer {
        return layer as! AVCaptureVideoPreviewLayer
    }
}