swift4 qr reader working but no result - swift

Question

swift4 qr-code reader and suppose to popup an alert, but it didn't show the popup alert.
The session start running properly, but the func captureOutput() seems not trigger when qr-code scanned.
my code:
import UIKit
import AVFoundation
class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
#IBOutlet weak var square: UIImageView!
//Creating session
var video = AVCaptureVideoPreviewLayer()
override func viewDidLoad() {
super.viewDidLoad()
//Creating session
let session = AVCaptureSession()
//Define capture devcie
let captureDevice = AVCaptureDevice.default(for: AVMediaType.video)
do
{let input = try AVCaptureDeviceInput(device: captureDevice!)
session.addInput(input)}
catch
{ print ("ERROR")}
let output = AVCaptureMetadataOutput()
session.addOutput(output)
output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
output.metadataObjectTypes = [AVMetadataObject.ObjectType.qr]
video = AVCaptureVideoPreviewLayer(session: session)
video.frame = view.layer.bounds
view.layer.addSublayer(video)
self.view.bringSubview(toFront: square)
session.startRunning()
}
func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
if metadataObjects != nil && metadataObjects.count != 0
{
if let object = metadataObjects[0] as? AVMetadataMachineReadableCodeObject
{
if object.type == AVMetadataObject.ObjectType.qr
{
let alert = UIAlertController(title: "QR Code", message: object.stringValue, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Retake", style: .default, handler: nil))
alert.addAction(UIAlertAction(title: "Copy", style: .default, handler: { (nil) in
UIPasteboard.general.string = object.stringValue
}))
present(alert, animated: true, completion: nil)
}
}
}
}
}

Answer 1

Your scanning code check will be in the following delegate:
func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection)
Your code will be like this:
import UIKit
import AVFoundation
class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
#IBOutlet weak var square: UIImageView!
//Creating session
var video = AVCaptureVideoPreviewLayer()
override func viewDidLoad() {
super.viewDidLoad()
//Creating session
let session = AVCaptureSession()
//Define capture devcie
let captureDevice = AVCaptureDevice.default(for: AVMediaType.video)
do
{let input = try AVCaptureDeviceInput(device: captureDevice!)
session.addInput(input)}
catch
{ print ("ERROR")}
let output = AVCaptureMetadataOutput()
session.addOutput(output)
output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
output.metadataObjectTypes = [AVMetadataObject.ObjectType.qr]
video = AVCaptureVideoPreviewLayer(session: session)
video.frame = view.layer.bounds
view.layer.addSublayer(video)
self.view.bringSubview(toFront: square)
session.startRunning()
}
func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
if metadataObjects != nil && metadataObjects.count != 0
{
if let object = metadataObjects[0] as? AVMetadataMachineReadableCodeObject
{
if object.type == AVMetadataObject.ObjectType.qr
{
let alert = UIAlertController(title: "QR Code", message: object.stringValue, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Retake", style: .default, handler: nil))
alert.addAction(UIAlertAction(title: "Copy", style: .default, handler: { (nil) in
UIPasteboard.general.string = object.stringValue
}))
present(alert, animated: true, completion: nil)
}
}
}
}
}