I'm trying to use a Swift class from hackingswift.com that reads QR codes. This code has apparently been used in the past by posters to this forum, but it doesn't work now in Swift 5.5. I get an error 'expression failed to parse, unknown error' on the line

    view.layer.addSublayer(previewLayer)

in the following. Any help would be appreciated.

//: A UIKit based Playground for presenting user interface
  
import AVFoundation
import UIKit
import PlaygroundSupport

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!

    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))
            found(code: stringValue)
        }

        dismiss(animated: true)
    }

    func found(code: String) {
        print(code)
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}

// Present the view controller in the Live View window
PlaygroundPage.current.liveView = ScannerViewController()

CodePudding user response：

.addSublayer is working as expected.

You can try out the sample code below in the playground for testing.

let view = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
view.backgroundColor = .cyan

let layer = CALayer()

layer.bounds = CGRect(x: 0, y: 0, width: 100, height: 100)
layer.position = CGPoint(x: 200/2, y: 200/2)
layer.backgroundColor = UIColor.magenta.cgColor
layer.borderWidth = 5
layer.borderColor = UIColor.black.cgColor

view.layer.addSublayer(layer)
PlaygroundPage.current.liveView = view

I rapidly tried the sample code you provided in Playgrounds and AVCaptureDevice.default(for: .video) seems to fail.

CodePudding user response：

This is an annoying bug in playgrounds. Leaving aside for a moment that there is no capture device available in playgrounds or the simulator, so none of this will work anyway, the fix is to treat view as an optional:

view?.layer.addSublayer(previewLayer)

I have no idea why this is the case, and nor do some other people