Barcode on swift 4

问题:

I'm trying to upgrade mi app to swift 4, but the barcode reader is not working.

I have isolated the barcode reader code, and still not working. The camera works but it does not detect the barcode.

The code worked just fine on swift 3 iOS 10.

This is the complete 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
}
}

I am using iOS 11 on my iPhone, upgraded to beta 9.

Any idea? Thank you.

回答1:

I figured it out but Apple didn't make it so obvious. The callback function from the delegate AVCaptureMetadataOutputObjectsDelegate has been renamed and the parameter names are different!

So, replace

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!)

to

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

My view controller is now scanning QR Codes as before after this. It has the same parameters but the first parameter name is different. Change the function and parameter names and build/run.

Hope this helps!

回答2:

After changing the delegate call back :

From

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!)

To

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

I need to set all available types for metadataObjectTypes too as below-

output.metadataObjectTypes=output.availableMetadataObjectTypes

回答3:

After changing your code from:

func metadataOutput(captureOutput: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {}

to:

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

everything works again.