"Barcode Found" but result handler not called

Hello, I'm using the following code to scan for a QR code, apparently the scanning works because when pointing the camera to a QR code [ZXing.Net.Mobile] Barcode Found is logged from ZXing, however my defined HandleScanResult function is not called, am I registering the callback wrong?

        void scan()
        {
            var opts = new MobileBarcodeScanningOptions
            {
                PossibleFormats = new List<ZXing.BarcodeFormat> {
                    ZXing.BarcodeFormat.DATA_MATRIX,
                    ZXing.BarcodeFormat.QR_CODE
                },
                CameraResolutionSelector = availableResolutions => {

                    foreach (var ar in availableResolutions)
                    {
                        Console.WriteLine("Resolution: " + ar.Width + "x" + ar.Height);
                    }
                    return null;
                }
            };

            scanFragment.StartScanning(HandleScanResult, opts);

        }

        private void HandleScanResult(ZXing.Result obj)
        {
            if (obj.Text.IsNullOrEmpty()) //BREAKPOINT HERE, NEVER REACHED
            {
                return;
            }
        }

When googling further I found this issue: #643 implementing the solution suggested by @ElteHupkes (thank you very much btw! :)) seems to resolve this issue.
I'll leave this issue open as I think this could use either a fix or some documentation.

[knocte]

What version of ZXing.Net.Mobile are you using?

I'm using the following packages:
ZXing.Net.Mobile.Core, Version=2.4.1.0
ZXing.Net.Mobile.Forms, Version=2.4.1.0
ZXing.Net.Mobile.Forms.Android, Version=2.4.1.0
ZXingNetMobile, Version=2.4.1.0
zxing.portable, Version=0.16.2.0

[knocte]

I'm using the following packages:
ZXing.Net.Mobile.Core, Version=2.4.1.0
...

Well, the reason of why the issue you referenced is closed is because it could be already fixed in the 3.0.0-beta version. Please test this version.

[Cheesebaron]

Running 3.0.0-beta5 and still have this issue on Android.

ZXing spits out Barcode found in debug output, but callback is not triggered. Code used is very similar to the code in the first post. Not entirely sure what is going on. Linker is set to none, so shouldn't be that.

It is reproducible in the FragmentActivity sample callback doesn't get triggered. Will debug it a bit :)

[Cheesebaron]

It is a timing issue it seems.

scanner in ZXingScannerFragment gets set up in OnCreateView which is a lifecycle method. However, in the FragmentActivity code the call to StartScanning happens after the Fragment is initialized. This means that OnCreateView hasn't been called yet, and the internal Scan() method isn't called due to scanner being null and callback is never hooked up.

In short. StartScanning is called before OnCreateView in ZXingScannerFragment, leading to no callback being triggered.

I believe you are correct, in the end a coworker implemented a workaround for this, looking at our code he added a delay before setting up the scanner. The whole setup etc is still called in OnCreateView

        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)
        {
            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            var lbNotGrantedPermission = Array.Exists<Permission>(grantResults, permission => permission != Permission.Granted);

            if (lbNotGrantedPermission == true)
            {
                // Some permissions were not granted
                moCameraPermissionsDescription.Visibility = ViewStates.Visible;
            }
            else
            {
                // All permissions were granted
                Handler loHandler = new Handler();
                Action loAction = () =>
                {
                    SetUpScanner();
                };

                // We need some delay due to animated transition between the fragments. Also, without delay
                // the scanner don't work right after permissions were granted(only the first time)
                loHandler.PostDelayed(loAction, miSetupScannerDelay);
            }
        }

[ElteHupkes]

@Cheesebaron Yes, that was exactly my conclusion here: #643 (comment). I actually thought this had been resolved by now. Anyway, the workaround I added there probably still does the trick.

[Cheesebaron]

Ah, yes. You are right. Not sure what the better approach would be though. I don't like the delay code.

Perhaps, just check if callback was set in OnCreateView, and call StartScanning if so. This way it doesn't automatically start scanning if someone didn't call StartScanning already.