Question

我正在关注有关如何从ipad相机捕获条形码扫描仪的教程，这是所编写的代码。该教程是用xcode 8编写的，而我使用的是Xcode10。出现了

错误

“可选类型'AVCaptureDevice？的值？必须解包到类型'AVCaptureDevice'的值”

在do try catch语句中

。有人可以告诉我在这种情况下处理可选值的正确方法吗？当我将行更改为“让输入=尝试AVCaptureDeviceInput（device：captureDevice！）”时该应用程序崩溃。

import AVFoundation
import UIKit

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var video = AVCaptureVideoPreviewLayer()    //contains what the camera is pointing at

    override func viewDidLoad() {
        super.viewDidLoad()

        //creates session
        let session = AVCaptureSession()

        //define capture device
        let captureDevice = AVCaptureDevice.default(for: AVMediaType.video)

        do{
            let input = try AVCaptureDeviceInput(device: captureDevice)//Error occurs here
            session.addInput(input) //input coming from camera
        }
        catch{
            print("Error")
        }
        let output = AVCaptureMetadataOutput()
        session.addOutput(output)

        output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        output.metadataObjectTypes = [AVMetadataObject.ObjectType.code93, AVMetadataObject.ObjectType.code39]   //may need to change this based on barcode type
        video = AVCaptureVideoPreviewLayer(session: session)
        video.frame = view.layer.bounds
        view.layer.addSublayer(video)
        session.startRunning()

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

}

Answer 1

当我搜索此问题的答案时，它仅显示您的问题。然后，我从同事那里寻求帮助，并最终使它顺利运行。尝试下面的代码。

let captureDevice = AVCaptureDevice.default(for: .video)

do{
     let input = try AVCaptureDeviceInput(device: captureDevice!)
         if self.session.canAddInput(input) {
              self.captureSession.addInput(input)
         }
}
catch{
        print("Error")
}

可选类型“ AVCaptureDevice？”的值必须解包为'AVCaptureDevice'类型的值

1 个答案: