title: Barcode on swift 4
body: <p>I'm trying to upgrade mi app to swift 4, but the barcode reader is not working.</p>
  
  <p>I have isolated the barcode reader code, and still not working. The camera works but it does not detect the barcode.</p>
  
  <p>The code worked just fine on swift 3 iOS 10.</p>
  
  <p>This is the complete code</p>
  
  
  
  <pre><code>import AVFoundation
  import UIKit
  
  class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
  var captureSession: AVCaptureSession!
  var previewLayer: AVCaptureVideoPreviewLayer!
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      view.backgroundColor = UIColor.black
      captureSession = AVCaptureSession()
  
      let videoCaptureDevice = AVCaptureDevice.default(for: AVMediaType.video)
      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 = [AVMetadataObject.ObjectType.ean8, AVMetadataObject.ObjectType.ean13, AVMetadataObject.ObjectType.pdf417]
      } else {
          failed()
          return
      }
  
      previewLayer = AVCaptureVideoPreviewLayer(session: captureSession);
      previewLayer.frame = view.layer.bounds;
      previewLayer.videoGravity = AVLayerVideoGravity.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 captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
      captureSession.stopRunning()
  
      if let metadataObject = metadataObjects.first {
          let readableObject = metadataObject as! AVMetadataMachineReadableCodeObject;
  
          AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
          found(code: readableObject.stringValue!);
      }
  
      dismiss(animated: true)
  }
  
  func found(code: String) {
      print(code)
  }
  
  override var prefersStatusBarHidden: Bool {
      return true
  }
  
  override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
      return .portrait
  }
  }
  </code></pre>
  
  <p>I am using iOS 11 on my iPhone, upgraded to beta 9.</p>
  
  <p>Any idea? Thank you.</p>