屏幕在捕获QR时卡住；“第二次”；在我的IOS应用程序中

在我的应用程序中，我需要阅读QA代码。这是它第一次在二维码中显示字符串。但当我第二次尝试使用它时。它被困在捕获照片模式中，但支持代码流正在运行

import UIKit
import AVFoundation

class BarCodeViewController: UIViewController,AVCaptureMetadataOutputObjectsDelegate {

var captureSession: AVCaptureSession!
var previewLayer: AVCaptureVideoPreviewLayer!
let appDelegat : AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = UIColor.blackColor()
    captureSession = AVCaptureSession()

    let videoCaptureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    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: dispatch_get_main_queue())
        metadataOutput.metadataObjectTypes = [AVMetadataObjectTypeQRCode]
    } else {
        failed()
        return
    }

    previewLayer = AVCaptureVideoPreviewLayer(session: captureSession);
    previewLayer.frame = view.layer.bounds;
    previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    view.layer.addSublayer(previewLayer);

    captureSession.startRunning();

       }

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


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, handler: nil))
    presentViewController(ac, animated: true, completion: nil)
    captureSession = nil
}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

    if (captureSession?.running == false) {
        captureSession.startRunning();
    }
}

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(animated)

    if (captureSession?.running == true) {
        captureSession.stopRunning();
    }
}

func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {
    captureSession.stopRunning()

    if let metadataObject = metadataObjects.first {
        let readableObject = metadataObject as! AVMetadataMachineReadableCodeObject;

        AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
        foundCode(readableObject.stringValue);
    }


}

func foundCode(code: String) {
    var x = code.componentsSeparatedByString("-")

    let productProfile = ProductDetailViewController(nibName: "ProductDetailViewController", bundle: nil)


    productProfile.ProductCode = x[1]
        dismissViewControllerAnimated(true, completion: nil)


    appDelegat.centerContainer!.centerViewController = productProfile
}

override func prefersStatusBarHidden() -> Bool {
    return true
}

override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
    return .Portrait
    }
}

我试过了，但想不出来。。请帮我做这件事

func foundCode(code: String) {
    var x = code.componentsSeparatedByString("-")
    let productProfile = ProductDetailViewController(nibName:                   "ProductDetailViewController", bundle: nil)
    productProfile.ProductCode = x[1]
    captureSession.stopRunning()
        dismissViewControllerAnimated(true, completion: nil)
   self.navigationController?.popViewControllerAnimated(false)
  appDelegat.centerContainer!.centerViewController = productProfile
}

添加了

self.navigationController？.popViewControllerAnimated（false）

添加了

self.navigationController？.popViewControllerAnimated（false）