Reinitializing barcode reader when viewWillAppear (again) - ios

Question

I got a barcode reader that correctly initialize the first time the view is loaded. However when I go back to the view the video feed stops working.
The code below shows how is initialized in the viewDidLoad method. Any suggestion on how to modify it so I can call part of it when the viewWillAppear (again)?
Code:
override func viewDidLoad() {
super.viewDidLoad()
// Get an instance of the AVCaptureDevice class to initialize a device object and provide the video
// as the media type parameter.
let captureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
// Get an instance of the AVCaptureDeviceInput class using the previous device object.
var error:NSError?
let input: AnyObject! = AVCaptureDeviceInput.deviceInputWithDevice(captureDevice, error: &error)
if (error != nil) {
// If any error occurs, simply log the description of it and don't continue any more.
println("\(error?.localizedDescription)")
return
}
// Initialize the captureSession object.
captureSession = AVCaptureSession()
// Set the input device on the capture session.
captureSession?.addInput(input as AVCaptureInput)
// Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
let captureMetadataOutput = AVCaptureMetadataOutput()
captureSession?.addOutput(captureMetadataOutput)
// Set delegate and use the default dispatch queue to execute the call back
captureMetadataOutput.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue())
captureMetadataOutput.metadataObjectTypes = supportedBarCodes
// Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
//videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
var tmpbounds=view.layer.bounds;
videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill;
videoPreviewLayer?.bounds = tmpbounds
videoPreviewLayer?.position = CGPointMake(CGRectGetMidX(tmpbounds), CGRectGetMidY(tmpbounds))
// videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspect
videoPreviewLayer?.frame = view.layer.bounds
view.layer.addSublayer(videoPreviewLayer)
// Start video capture.
captureSession?.startRunning()
// Move the message label to the top view
view.bringSubviewToFront(messageLabel)
// Initialize QR Code Frame to highlight the QR code
qrCodeFrameView = UIView()
qrCodeFrameView?.layer.borderColor = UIColor.greenColor().CGColor
qrCodeFrameView?.layer.borderWidth = 2
view.addSubview(qrCodeFrameView!)
view.bringSubviewToFront(qrCodeFrameView!)
}

Answer 1

try to execute on viewDidAppear
captureSession?.startRunning()
on viewWillDissapear
captureSession?.stopRunning()
Also register for notification AVCaptureSessionRuntimeErrorNotification and log all errors. I think it will help you to understand what going wrong.

Answer 2

You are setting up the captureSession and the videoPreviewLayer in viewDidLoad. That is only run when the ViewController is created. You need to move some code to viewDidAppear, which will run each time this view appears. Most simply, move all the code from this line:
captureSession = AVCaptureSession()
onwards into viewDidAppear.