Assign @state var from SwiftUIView in UIViewController

Question

I would like put a @State var from my SwiftUIView in my UIViewController. My UIViewController is a scanner/reader qr code and when it detect QRCode i would like that my state var update automatically and assign my state var to the url found. I don't know where is the problem, here is the code :

ContentView.swift :

import SwiftUI
struct ContentView: View {

    @State var url = "url"

    var body: some View {
                VStack {
                    SCRepresentable(test: $url)
                    Text(test)
                        .font(.title)
                        .foregroundColor(.white)
                }.padding(.bottom, 2)
        }
    }

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

ScannerViewController.swift (LOOK THE FUNCTION METADATOUTPUT where i try self.url = stringValue(the url found when qr code is detected)) :

import AVFoundation
import UIKit
import SwiftUI

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    var url: String = "url"


    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor.black
        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]
        } else {
            failed()
            return
        }

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

        captureSession.startRunning()
    }


    func failed() {
        let ac = UIAlertController(title: "Scanning not supported", message: "Your device does not support scanning a code from an item. Please use a device with a camera.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
        captureSession = nil
    }

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

        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))
           self.url = stringValue
            found(code: stringValue)
        }

        dismiss(animated: true)
    }

    func found(code: String) {
        print(code)
        print("url: ", self.url)
    }

    func rrr() -> String{
        return self.url
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}

SCRepresentable.swift :

import SwiftUI

struct SCRepresentable: UIViewControllerRepresentable {

    @Binding var test: String


    typealias UIViewControllerType = ScannerViewController

    func makeUIViewController(context: UIViewControllerRepresentableContext<SCRepresentable>) -> ScannerViewController {
        let scan = ScannerViewController()
        test = scan.url
        return scan
    }

    func updateUIViewController(_ uiViewController: ScannerViewController, context: UIViewControllerRepresentableContext<SCRepresentable>) {
        //Add anything
    }
}

Thanks for your help !

Answer 1

Hello there I see that you want to handle when the QR code detected you don't need an annotation @State, you need to bind the viewController with @Binding let me explain it more in code:

in ScannerViewController we need to declare @Binding var urlDetected: String that require to be initialized in init() we call this func:

init(urlDetected: Binding<String>) {
        _urlDetected = urlDetected
        super.init(nibName: nil, bundle: nil) 
    }

that require to pass another binding variable in SCRepresentable @Binding var urlDetected: String

func makeUIViewController(context: UIViewControllerRepresentableContext<SCRepresentable>) -> ScannerViewController {
        let scan = ScannerViewController(isDetected: $urlDetected)
        return scan
    }

so now you have this var urlDetected in SCRepresentable when you declare it in the

struct ContentView: View {

    @State var url = "url"

    var body: some View {
                VStack {
                    SCRepresentable(urlDetected: $url)
....<#Code#>

when the url inside the viewController changes it will notify and update the view

but don't forget to set a value inside the viewController like this self. urlDetected = .constant(stringValue