IOS App crash with Null Reference Exception at SetupCaptureSession() about zxing.net.mobile

[jamesingreersc]

@spinspin Thanks for this. It helped a bunch!

[spinspin]

@jamesingreersc Did you find a solution to this? I'm running into the same issue .

[jamesingreersc]

@spinspin No, I found nothing helpful. I can see that the UINavigationController is null when the scanner is being initialized. I'm not sure if this a bug in .Net or not. I am going to test the old version of the app that does work and see if it's null there or not.

[spinspin]

It's probably a bug. I've just written some native net7.0-ios code which handles barcode scanning so I don't need to use this library let me know if you want it.

[jamesingreersc]

@spinspin That would be awesome if I could use your code. Thanks bunches!!

[spinspin]

@jamesingreersc this should be enough to get going , I'm using MvvmCross but the core functionality to create a barcode scanner is in here

public class BarcodeScannerViewController : MvxViewController
{
AVCaptureSession captureSession;
AVCaptureVideoPreviewLayer previewLayer;
public Action BarcodeScanned { get; set; }

    public BarcodeScannerViewController(IntPtr handle) : base(handle) { }

    public BarcodeScannerViewController(){}

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();
        SetUI();
        StartScanning();
    }

    private void SetUI()
    {        
        View.BackgroundColor = UIColor.White;

        NavigationController.NavigationBar.TitleTextAttributes = new UIStringAttributes
        {
            Font = UIFont.FromName("Gill Sans", 20),
            ForegroundColor = UIColor.Black
        };

        NavigationItem.BackButtonTitle = "";
        NavigationItem.Title = "Barcode Scanning";

        var closeImage = UIImage.FromBundle("Close36pt").ImageWithRenderingMode(UIImageRenderingMode.AlwaysTemplate);

        if (DeviceInfo.Version.Major >= 13)
        {
            closeImage.ApplyTintColor(UIColor.Black);
        }

        var closeButton = new UIButton();
        closeButton.SetImage(closeImage, UIControlState.Normal);
        closeButton.TintColor = UIColor.Black;
        NavigationItem.SetRightBarButtonItem(new UIBarButtonItem(closeButton),true);

        closeButton.TouchUpInside += (sender, args) =>
        {
            ViewModel.OnBarcodeScanCancel();
        };
    }


    void StartScanning()
    {
        try
        {
            captureSession = new AVCaptureSession();
            var videoCaptureDevice = AVCaptureDevice.GetDefaultDevice(AVMediaTypes.Video);
            // Create an input from the video capture device
            var videoInput = AVCaptureDeviceInput.FromDevice(videoCaptureDevice, out NSError error);

            if (error != null)
            {
                ViewModel.OnBarcodeScanError();
                return;
            }
            else
            {
                captureSession.AddInput(videoInput);
            }

            // Create a metadata output and set its delegate
            var metadataOutput = new AVCaptureMetadataOutput
            {
                RectOfInterest = UIScreen.MainScreen.Bounds
            };

            metadataOutput.SetDelegate(new OutputDelegate(DidScanBarcode), DispatchQueue.MainQueue);
            captureSession.AddOutput(metadataOutput);
            metadataOutput.MetadataObjectTypes = AVMetadataObjectType.EAN13Code
                                   | AVMetadataObjectType.QRCode
                                   | AVMetadataObjectType.EAN8Code
                                   | AVMetadataObjectType.Code128Code;

            // Create a preview layer to show the view from the camera
            previewLayer = new AVCaptureVideoPreviewLayer(captureSession)
            {
                Frame = new CGRect(View.Bounds.X, View.Bounds.Y +50 , View.Bounds.Width, View.Bounds.Height-50)
            };


            View.Layer.AddSublayer(previewLayer);

            // Create a new UIView with the desired dimensions.
            var redLineView = new UIView
            {
                BackgroundColor = UIColor.Red,
                Frame = new CGRect(0, previewLayer.Frame.GetMidY(), View.Bounds.Width, 2) // This line is 2 points thick and centered in the preview layer.
            };

            // Add the view to the parent view.
            View.AddSubview(redLineView);

            // Start the capture session
            captureSession.StartRunning();
        }

        catch (Exception)
        {
            ViewModel.OnBarcodeScanError();
        }
    }

    private void DidScanBarcode(string barcode)
    {
        // Stop the capture session and notify the delegate
        captureSession.StopRunning();
        captureSession.Dispose(); // release the capture session
        captureSession = null; // set it to null

        // Remove the preview layer
        previewLayer.RemoveFromSuperLayer();
        previewLayer.Dispose(); // Dispose the preview layer
        previewLayer = null; // set it to null

        ViewModel.OnBarcodeScanSuccess(barcode);
    }


    public override void ViewWillDisappear(bool animated)
    {
        base.ViewWillDisappear(animated);

        if (IsBeingDismissed || IsMovingFromParentViewController)
        {
            Cleanup();
        }
    }

    void Cleanup()
    {
        // Stop the capture session and release resources
        captureSession.StopRunning();
        captureSession.Dispose();
        captureSession = null;

        previewLayer.RemoveFromSuperLayer();
        previewLayer.Dispose();
        previewLayer = null;
    }
}

class OutputDelegate : AVCaptureMetadataOutputObjectsDelegate
{
    Action<string> barcodeHandler;

    public OutputDelegate(Action<string> barcodeHandler)
    {
        this.barcodeHandler = barcodeHandler;
    }

    public override void DidOutputMetadataObjects(AVCaptureMetadataOutput captureOutput, AVMetadataObject[] metadataObjects, AVCaptureConnection connection)
    {
        if (metadataObjects != null && metadataObjects.Length > 0)
        {
            var readableObject = metadataObjects[0] as AVMetadataMachineReadableCodeObject;

            if (readableObject != null)
            {
                var barcode = readableObject.StringValue;
                barcodeHandler?.Invoke(barcode);
            }
        }
    }
}

public interface IBarcodeScanningServiceDelegate
{
    void DidFinishScanning(string barcode);
}