Xcode 9 / Swift 4 AVCaptureMetadataOutput setMetadataObjectTypes使用availableMetadataObjectTypes

似乎有很多与我遇到的问题类似的问题：

AVmetadata迅速更改4 xcode 9

找到了AVCaptureMetadataOutput setMetadataObjectTypes不支持的类型

还有一个与AVFoundation有关的Apple错误：

https://forums.developer.apple.com/thread/86810#259270

但是这些似乎都不是我的答案。
我的代码可以在swift 3中很好地运行，但是只会在swift 4中出错。使用以上链接中的解决方案根本不会产生任何变化。

码：

import UIKit
import AVFoundation

class BarCodeScanViewController: UIViewController,     AVCaptureMetadataOutputObjectsDelegate {
weak var delegate: FlowControllerDelegate?

var captureSession: AVCaptureSession = AVCaptureSession()
var previewLayer: AVCaptureVideoPreviewLayer = 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.canAddInput(videoInput)
    } else {
        failed()

        return
    }

    // let captureMetadataOutput = AVCaptureMetadataOutput()
    let metadataOutput = AVCaptureMetadataOutput()

    if captureSession.canAddOutput(metadataOutput) {
        captureSession.addOutput(metadataOutput)

        // Check status of camera permissions
        metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
//            metadataOutput.metadataObjectTypes = [AVMetadataObject.ObjectType.upce]
        metadataOutput.metadataObjectTypes = [.ean8, .ean13, .pdf417, .upce]
    } 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) {
    if captureSession.isRunning == true {
        captureSession.stopRunning()
    }

    super.viewWillDisappear(animated)
}

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

    if let metatdataObject = metadataObjects.first {
        guard let readableObject = metatdataObject 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
}
}

当我在Xcode 8和Swift 3中构建此代码时，它工作正常。当我在Xcode 9中运行它时，Swift 4it在添加媒体类型时崩溃：

metadataOutput.metadataObjectTypes = [.ean8, .ean13, .pdf417, .upce]

在这两种情况下，我都将构建到以前没有Beta的iOS 11设备。

我尝试使用“ __”来查看是否是上面提到的Apple bug。如果我注释掉该行，则代码会运行，但不会捕获。

苹果可能还会引入其他错误吗？还有谁有相同的问题吗？

任何帮助，将不胜感激。

谢谢