SWIFT Scan QRCode

import UIKit
import Foundation
import AVFoundation

class ViewController: UIViewController,AVCaptureMetadataOutputObjectsDelegate,UIAlertViewDelegate {

    let device = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    let session = AVCaptureSession()
    var layer:AVCaptureVideoPreviewLayer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = UIColor.grayColor()
        let lblIntroduction = UILabel(frame: CGRectMake(10, 80, 300, 50))
        lblIntroduction.text = "Scan QRCode"
        lblIntroduction.textColor = UIColor.whiteColor()
        self.view.addSubview(lblIntroduction)
        
        //let imageView = UIImageView(frame: CGRectMake(10, 140, 300, 300))
        //imageView.image = UIImage(named: "pick_bg")
        //self.view.addSubview(imageView)
        
        //add scan line effect
        let line = UIView(frame: CGRectMake(20, 150, 280, 1))
        line.backgroundColor = UIColor.yellowColor()
        self.view.addSubview(line)
        
        UIView.animateWithDuration(2.5, delay: 0, options: UIViewAnimationOptions.Repeat, animations: { () -> Void in
              line.frame = CGRectMake(20, 430, 280, 1)
            }, completion: nil)


        setupCamera()
    }
    
    func setupCamera() {
        //An AVCaptureSession preset suitable for medium quality output
        self.session.sessionPreset = AVCaptureSessionPresetMedium //AVCaptureSessionPresetHigh
        var error:NSError?
        //This step is to ask device where it can use back camera
        let input = AVCaptureDeviceInput(device: device, error: &error)
        if error != nil {
            println(error?.description)
            return
        }
        
        if session.canAddInput(input) {
            session.addInput(input)
        }
        
        layer = AVCaptureVideoPreviewLayer(session: session)
        layer?.videoGravity = AVLayerVideoGravityResizeAspectFill
        layer?.frame = CGRectMake(20, 150, 280, 280)
        self.view.layer.insertSublayer(self.layer!, atIndex: 0)
        
        let output = AVCaptureMetadataOutput()
        output.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue())
        if session.canAddOutput(output) {
            session.addOutput(output)
            output.metadataObjectTypes = [AVMetadataObjectTypeQRCode]
        }
        
        session.startRunning()
        
    }
    
    
    func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {
        var stringValue:String?
        if metadataObjects.count > 0 {
            var metadataObject = metadataObjects[0] as! AVMetadataMachineReadableCodeObject
            stringValue = metadataObject.stringValue
        }
        
        self.session.stopRunning()
        let alertView = UIAlertView()
        alertView.message = stringValue
        alertView.addButtonWithTitle("Sure")
        alertView.delegate = self
        alertView.cancelButtonIndex = 0
        alertView.show()
    }
    
    func alertView(alertView: UIAlertView, clickedButtonAtIndex buttonIndex: Int) {
        session.startRunning()
    }

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


}