AVCaptureMetadataOutputObjectsDelegate method not called

Question

I have a ViewController that continuously scans for QR codes and implements AVCaptureMetadataOutputObjectsDelegate to retrieve the metadata output.

class ScanViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    var captureSession = AVCaptureSession()
    var videoPreviewLayer: AVCaptureVideoPreviewLayer?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Get the back-facing camera for capturing videos
        let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDualCamera], mediaType: AVMediaTypeVideo, position: .back)

        guard let captureDevice = deviceDiscoverySession?.devices.first else {
            print("Failed to get the camera device")
            return
        }

        do {
            // Get an instance of the AVCaptureDeviceInput class using the previous device object.
            let input = try AVCaptureDeviceInput(device: captureDevice)

            // Set the input device on the capture session.
            captureSession.addInput(input)

            // Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
            let captureMetadataOutput = AVCaptureMetadataOutput()
            captureSession.addOutput(captureMetadataOutput)

            // Set delegate and use the default dispatch queue to execute the call back
            captureMetadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            captureMetadataOutput.metadataObjectTypes = [AVMetadataObjectTypeQRCode]

        } catch {
            // If any error occurs, simply print it out and don't continue any more.
            print(error)
            return
        }

        // Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
        videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
        videoPreviewLayer?.frame = view.layer.bounds
        view.layer.addSublayer(videoPreviewLayer!)

        // Start video capture.
        captureSession.startRunning()
    }

    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        print("in function of extension")
        // Check if the metadataObjects array is not nil and it contains at least one object.
        if metadataObjects.count == 0 {
            print("nada qr code")
            return
        }

        // Get the metadata object.
        let metadataObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject

        if metadataObj.type == AVMetadataObjectTypeQRCode {
            if metadataObj.stringValue != nil {
                print(metadataObj.stringValue)
            }
        }
    }
}

But for some reason the delegate callback doesn't get called. In the tutorial I'm following, it runs perfectly.

Hopefully someone can provide any words of assistance. Anything would be immensely helpful to get me on the right track. Thanks so much in advance.

What do you mean by 'isn't running'? Is the function getting called? — Xcoder, Jan 29 '18 at 21:54
@MilanNosáľ weird. doesn't run when i move it into the main class under viewdidload(). put a print statement inside and doesnt print — Theo Strauss, Jan 29 '18 at 22:48
let's clean up the comments.. so it's still not working, am I right? — Milan Nosáľ, Jan 29 '18 at 22:54
haha cool. yes, its not working, not even entering into the function. — Theo Strauss, Jan 29 '18 at 22:55
xcode 9.2 beta, ios 11, swift 4. i also tried using captureOutput(_ output...) instead of metadataOutput(_ output...) but that didn't work as well — Theo Strauss, Jan 29 '18 at 23:02
weird, it says that `AVMediaTypeVideo` has been renamed to `AVMediaType.video`.. I don't understand how could you compile that code under swift 4 — Milan Nosáľ, Jan 29 '18 at 23:05
@MilanNosáľ just saw i'm using swift 3.2! think that would solve the entire problem? — Theo Strauss, Jan 29 '18 at 23:11
try to change it, and we will see.. I doubt it but who knows? — Milan Nosáľ, Jan 29 '18 at 23:12
how does `ScanViewController` fit into the project? I downloaded the template from the link you provided and there is no class named `ScanViewController` — Milan Nosáľ, Jan 29 '18 at 23:17
@MilanNosáľ sorry lost wifi. Changing Swift might harm a bunch of files in my project. Holding off on that for now. Scan view controller relates directly to QRScannerController. Didn't include the labels, etc that they did. Thanks so much for investing so much time into this question! — Theo Strauss, Jan 30 '18 at 02:07

score 1 · Answer 1 · answered Jan 30 '18 at 23:24

The reason for not running is that metadataOutput(...) is technically a built-in function of the AV framework, but only for Swift 4. In Swift 3.0 and 3.2, the correct function is:

captureOutput(_ output: _AVCaptureOutput!, didOutputMetadataObjects: [Any]!, from connection: AVCaptureConnection!)

That should run!

score 0 · Answer 2 · edited Jan 29 '18 at 22:09

0

The extension code you posted does not compile for me. I had to add public to the method declaration:

public func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {

I am using Swift 4.

edited Jan 29 '18 at 22:09

Xcoder

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answered Jan 29 '18 at 22:01

Rafał Sroka

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Hey thanks for answering! I added public but its still not entering. Any clue why? – Theo Strauss Jan 29 '18 at 22:08
Check this solution if nothing works for you in swift 4 : https://stackoverflow.com/a/55808404/6235958 – Nupur Sharma Apr 23 '19 at 09:44

Martin · Answer 3 · 2018-11-05T14:03:59.960

0

Change the code as follows. It may work, at least it worked for me. I am using Swift 4.2

captureMetadataOutput.metadataObjectTypes = captureDeviceOutput.availableMetadataObjectTypes

edited Nov 05 '18 at 14:03

answered Nov 05 '18 at 12:28

Martin

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AVCaptureMetadataOutputObjectsDelegate method not called

3 Answers3