iOS Swift Barcode Reading

Question

I have barcode scanning working in my app. After the barcode is detected I stop the capture session to allow processing of the barcode. However, after the barcode is processed I want the scanning controller to stay up and the next barcode scanned. I had assumed that starting the capture session (startRunning()) would do it but the image stays frozen. How can I start the capture session again?

Answer 1

To Stop The Session use this code

self.session.stopRunning()

To begin it agian, use this code

self.session.startRunning()

Here is all the code to implement a barcode scanner...

import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    let session         : AVCaptureSession = AVCaptureSession()
    var previewLayer    : AVCaptureVideoPreviewLayer!
    var highlightView   : UIView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        // Allow the view to resize freely
        self.highlightView.autoresizingMask =   
            UIViewAutoresizing.FlexibleTopMargin |
            UIViewAutoresizing.FlexibleBottomMargin |
            UIViewAutoresizing.FlexibleLeftMargin |
            UIViewAutoresizing.FlexibleRightMargin

        // Select the color you want for the completed scan reticle
        self.highlightView.layer.borderColor = UIColor.greenColor().CGColor
        self.highlightView.layer.borderWidth = 3

        // Add it to our controller's view as a subview.
        self.view.addSubview(self.highlightView)

        // For the sake of discussion this is the camera
        let device = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)

        // Create a nilable NSError to hand off to the next method.
        // Make sure to use the "var" keyword and not "let"
        var error : NSError? = nil

        let input : AVCaptureDeviceInput? =
            AVCaptureDeviceInput.deviceInputWithDevice(device, error: &error) 
                as? AVCaptureDeviceInput

        // If our input is not nil then add it to the session, otherwise we're kind of done!
        if input != nil {
            session.addInput(input)
        } else {
            // This is fine for a demo, do something real with this in your app. :)
            println(error)
        }

        let output = AVCaptureMetadataOutput()
        output.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue())
        session.addOutput(output)
        output.metadataObjectTypes = output.availableMetadataObjectTypes

        previewLayer =
            AVCaptureVideoPreviewLayer.layerWithSession(session) 
                as! AVCaptureVideoPreviewLayer
        previewLayer.frame = self.view.bounds
        previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
        self.view.layer.addSublayer(previewLayer)

        // Start the scanner. You'll have to end it yourself later.
        session.startRunning()
    }

    // This is called when we find a known barcode type with the camera.
    func captureOutput(
        captureOutput: AVCaptureOutput!, 
        didOutputMetadataObjects metadataObjects: [AnyObject]!,
        fromConnection connection: AVCaptureConnection!) {

        var highlightViewRect = CGRectZero
        var barCodeObject : AVMetadataObject!
        var detectionString : String!

        let barCodeTypes = [AVMetadataObjectTypeUPCECode,
            AVMetadataObjectTypeCode39Code,
            AVMetadataObjectTypeCode39Mod43Code,
            AVMetadataObjectTypeEAN13Code,
            AVMetadataObjectTypeEAN8Code,
            AVMetadataObjectTypeCode93Code,
            AVMetadataObjectTypeCode128Code,
            AVMetadataObjectTypePDF417Code,
            AVMetadataObjectTypeQRCode,
            AVMetadataObjectTypeAztecCode]

        // The scanner is capable of capturing multiple 2-dimensional barcodes in one scan.
        for metadata in metadataObjects {

            for barcodeType in barCodeTypes {

                if metadata.type == barcodeType {
                    barCodeObject = self.previewLayer.transformedMetadataObjectForMetadataObject(metadata as! AVMetadataMachineReadableCodeObject)
                    highlightViewRect = barCodeObject.bounds
                    detectionString = (metadata as! AVMetadataMachineReadableCodeObject).stringValue
                    self.session.stopRunning()
                    self.alert(detectionString)
                    break
                }
            }
        }

        println(detectionString)
        self.highlightView.frame = highlightViewRect
        self.view.bringSubviewToFront(self.highlightView)
    }        

    func alert(Code: String){
        let actionSheet:UIAlertController = 
            UIAlertController(
                title: "Barcode", 
                message: "\(Code)", 
                preferredStyle: UIAlertControllerStyle.Alert)

        // for alert add .Alert instead of .Action Sheet
        // start copy
        let firstAlertAction:UIAlertAction = 
            UIAlertAction(
                title: "OK",
                style: UIAlertActionStyle.Default, 
                handler: { (alertAction: UIAlertAction!) in
                // action when pressed
                self.session.startRunning()      
        })

        actionSheet.addAction(firstAlertAction)
        // end copy
        self.presentViewController(actionSheet, animated: true, completion: nil)
    }  
}