扫描QR码

Question

我有下面的类试图扫描一个QR代码。我只是因为某种原因不能让它起作用。我能够呈现这个ViewController，它是相机所看到的输出，但是每当我试图扫描QR时，什么都不会发生。

知道少了什么吗？

import AVFoundation
import UIKit

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 captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, 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
    }
}

我还为plist增加了以下价值：

key: Privacy - Camera Usage Description 
value: $(PRODUCT_NAME) camera use

Answer 1

扫描代码检查将在以下委托中进行：

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

您的代码将如下所示：

import AVFoundation
import UIKit

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
    }
}