How to clear the information from the Label.text? - swift

Question

I am developing a QR code reader application. Hier is my code:
var captureSession: AVCaptureSession?
var videoPreviewLayer: AVCaptureVideoPreviewLayer?
var qrCodeframeView: UIView?
#IBOutlet weak var CancelButton: UIButton!
#IBOutlet weak var Label: UILabel!
override func viewDidLoad() {
CancelButton.hidden = true
Label.hidden = true
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func ScanMe(sender: AnyObject) {
CancelButton.hidden = false
Label.hidden = false
let captureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
var error: NSError?
let input: AnyObject!
do {
input = try AVCaptureDeviceInput (device: captureDevice)
} catch let error1 as NSError{
error = error1
input = nil
}
if (error != nil){
print ("\(error?.localizedDescription)")
return
}
captureSession = AVCaptureSession()
captureSession?.addInput(input as! AVCaptureInput)
let captureMetadatOutput = AVCaptureMetadataOutput()
captureSession?.addOutput(captureMetadatOutput)
captureMetadatOutput.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue())
captureMetadatOutput.metadataObjectTypes = [AVMetadataObjectTypeQRCode]
videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
videoPreviewLayer?.frame = view.layer.bounds
view.layer.addSublayer(videoPreviewLayer!)
captureSession?.startRunning()
view.bringSubviewToFront(Label)
view.bringSubviewToFront(CancelButton)
qrCodeframeView = UIView()
qrCodeframeView?.layer.borderColor = UIColor.greenColor().CGColor
qrCodeframeView?.layer.borderWidth = 2
view.addSubview(qrCodeframeView!)
view.bringSubviewToFront(qrCodeframeView!)
}
func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {
if metadataObjects == nil || metadataObjects.count == 0 {
qrCodeframeView?.frame = CGRectZero
Label.text = "No QR code detected"
return
}
let metadateObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject
if metadateObj.type == AVMetadataObjectTypeQRCode {
let BarcodeObject = videoPreviewLayer?.transformedMetadataObjectForMetadataObject(metadateObj as AVMetadataMachineReadableCodeObject) as! AVMetadataMachineReadableCodeObject
qrCodeframeView?.frame = BarcodeObject.bounds
if metadateObj.stringValue != nil {
Label.text = metadateObj.stringValue
captureSession?.stopRunning()
}
}
}
#IBAction func Cancel(sender: AnyObject) {
CancelButton.hidden = true
Label.hidden = true
captureSession?.stopRunning()
qrCodeframeView?.removeFromSuperview()
videoPreviewLayer?.removeFromSuperlayer()
}
#IBAction func Open(sender: AnyObject) {
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
var PC : SecondSecondViewController = segue.destinationViewController as! SecondSecondViewController
PC.label1 = Label.text!
}
}
The problem is when I click the cancel button and go back to the previous viewcontroller, when I reopen the qr code scanner I see the last scanned code, displayed in the Label.text. Would you please help me how to clear the label and do not display the old code, because these codes must be used only once and if the users see the codes they will be able to use them again.

Answer 1

If you want without adding other callbacks:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
var PC : SecondSecondViewController = segue.destinationViewController as! SecondSecondViewController
PC.label1 = Label.text!
Label.text = ""
}
otherwise you have to catch the unwind segue when you come back from SecondSecondViewController and there set Label.text = ""

Answer 2

Just add this to where you exit from the QR (press cancel):
label.text = ""