Question

我正在制作一个QR码扫描仪应用程序，我的相机在其中找到该编码并必须隔离到另一个视图中。但是我可以选择另一种视图，因为如果在找到代码后调用self.performSegue，该应用程序将随机关闭。

如果我不打电话给segue，则打印代码，但相机冻结。如果我摆脱了警戒线，应用程序将无法关闭

import UIKit
import Firebase
import AVFoundation

class ScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    var intendedDest = String()
    var codex = String()

    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        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.global(qos: .userInteractive))
            metadataOutput.metadataObjectTypes = [.ean8, .ean13, .pdf417, .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()
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    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)
        }

        self.performSegue(withIdentifier: "toTimerView", sender: self)
    }

    func found(code: String) {
        // qr code found!
        print(code)
        codex = code
        print(codex)
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let destination = segue.destination as? TimerViewController {
            destination.intendedDestxx = intendedDest
        }
    }

    override var prefersStatusBarHidden: Bool {
        return true
    }

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }
}
'''

Answer 1

根据警告和崩溃消息，您将在后台线程中访问UI。
确保在主线程中调用了您的UI代码。

如果有后台线程，则可以通过以下方法修复它：

public class Test {
public static Scanner scan;
public static void main(String args[]) {
    //To check the length of args --> I take "check" array as an input for my method "eachCycleFCFS".
    for (int a = 0; a < args.length; a++) {
        check.add(args[a]);
    }
    try {
        String fileAddress = args[0];
        File fileInput  = new File(fileAddress); //Read
        scan = new Scanner(fileInput);
        int numProcesses  = scan.nextInt();
        ...
        for (int m = 0; m < numProcesses; m++) {
            int a = scan.nextInt();
            int b = scan.nextInt();
            int c = scan.nextInt();
            int io = scan.nextInt();
            ...
        }

    }   
    catch (Exception e){
        e.printStackTrace();
            System.out.printf(" Error: File not foundd. \n");
    }
}
public static void eachCycleFCFS (Queue<Process> processes, int numProcesses, Process[] allProcesses, Process[] original, Process[] realOriginal, ArrayList<String> check) {                
        File fileInput = new File("random-numbers.txt");
    Scanner randomInput = null;
    try {
        randomInput = new Scanner(fileInput);
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    if (check.size() == 2) {
        if (check.get(0).contains("verbose")) {
            //Produce the detailed output
        }
    }
    else {
        //Produce the simple output
    }
    while (terminatedProcesses != numProcesses) {
        if (check.size() == 2) {
            if (check.get(0).equals("--verbose")) {
                //Produce the detailed output
            }
        }
    }
}

在您的代码中，我看到您将自己设置为后台队列上图像流的委托。这意味着您的segue也被调用为背景。通过以下方法修复它：

blahblahblah$ java Scheduling2 --verbose input-1.txt
java.io.FileNotFoundException: --verbose (No such file or directory)
    at java.io.FileInputStream.open0(Native Method)
    at java.io.FileInputStream.open(FileInputStream.java:195)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at java.util.Scanner.<init>(Scanner.java:611)
    at Scheduling2.main(Scheduling2.java:18)
 Error: File not found.

Xcode App扫描QR码时随机关闭

1 个答案: