[Bug] DetectionSpeed.noDuplicates is not respected properly

[burekas7]

Hi,

@navaronbracke

I'm using the controller in order to catch scans, And I'm using the "barcodes" stream like that:

mobileScannerController!.barcodes.listen(scannerlistener);

But it seems that on each scan, 'scannerlistener' is running twice. Is it a bug?

[CarlosVallsCiscar]

I have the same problem. I use the same as you to listen to the barcodes, and I always get two calls to the handler.

mobile_scanner: ^5.1.1 Flutter 3.22.1

I have tested the problem on iOS, but the user who detected the problem was on android.

This is the logger, i'm only listening to the events.

flutter: INFO 2024-06-04 11:06:42.063180 QrScanner:  Instance of 'BarcodeCapture'
flutter: INFO 2024-06-04 11:06:42.063457 QrScanner:  Instance of 'BarcodeCapture'

I checked the result of the 'BarcodeCapture' and is only 1 barcode in barcodes list and the rawBytes list is the same in both.

The controller configuration

final MobileScannerController _controller = MobileScannerController(
      detectionSpeed: DetectionSpeed.noDuplicates,
      facing: CameraFacing.back,
      torchEnabled: false,
      formats: [BarcodeFormat.qrCode]
  );

For now, as I have the QR check in the main thread, I have used a lock to avoid problems.

[navaronbracke]

Thanks for the observations. I'll have to take a look at why the listener is called twice specifically.

[huideaki]

Currently having the same issue, the listener is getting called twice when scanning a barcode

[aimeykra]

Thank you guys for posting this. I am facing same issue: Scaffold 'A' opens scaffold 'B'. Scaffold 'B' opens Scaffold 'C' which has MobileScanner widget. in my OnDetect or Listener call back, I have a Navigator.pop(). When a QR code is scanned, it triggers 2 'pop' and I am being sent back to scaffold 'A' instead of Scaffold 'B'.

I noticed that the double call back was not happening all the time, per my test, I would say 7 or 8 out of 10.

I added a workaround in my code to ignore the second callback and it's all working fine now. my scenario is simple though, i only needed one single scan, may not be the case for others.

Thanks. AK

[tajjacob]

@

Thank you guys for posting this. I am facing same issue: Scaffold 'A' opens scaffold 'B'. Scaffold 'B' opens Scaffold 'C' which has MobileScanner widget. in my OnDetect or Listener call back, I have a Navigator.pop(). When a QR code is scanned, it triggers 2 'pop' and I am being sent back to scaffold 'A' instead of Scaffold 'B'.

I noticed that the double call back was not happening all the time, per my test, I would say 7 or 8 out of 10.

I added a workaround in my code to ignore the second callback and it's all working fine now. my scenario is simple though, i only needed one single scan, may not be the case for others.

Thanks. AK

@aimeykra can you share the code snippet? I'm also having the same issue

[aimeykra]

@tajjacob , I am not doing anything fancy, I am just saving a status in a boolean variable to indicate that i have already sent the scanned data.

here is my OnDetect:

onDetect: (capture) { final List<Barcode> barcodes = capture.barcodes; for (final barcode in barcodes) { if (!_isDataSent) { Navigator.pop<String>(context, barcode.rawValue ?? 'No data in QR'); _isDataSent = true; } }

Again, this is fine for my scenario. i have a single QR to scan at a time.

hope it helps. @aimeykra

[tajjacob]

@aimeykra thanks for the snippet! its working!

[navaronbracke]

I'm currently going to look into this, as this is now also affecting an internal app.

Edit: It seems that the noDuplicates mode is not working correctly. Even in the example app, using it does not prevent the same barcode from being passed to the detection callback.

[ahua666]

I have the same issue.

[ahua666]

Temporarily solved it through business code.

[burekas7]

@navaronbracke Is there any progress with this issue?

Thanks.

[navaronbracke]

I have not looked into this yet. Mostly busy with other things at the moment.

[Dohmanlechx]

Following this issue as I'm having the same problem. I don't intend to use DetectionSpeed.noDuplicates but I still get duplicated results (2 of each) despite I use detectionTimeoutMs: 2000.

[GRHgabriel]

I handle this issue temporarily like this:

String? lastScan;

void _handleBarcode(BarcodeCapture barcodes) async { String? data = barcodes.barcodes.first.rawValue;

if (lastScan == data) {
  return;
}

lastScan = data;

 //your process code here....

}

[YahiaAngelo]

Adding autoStart: false to the controller solved it for me:

final MobileScannerController controller = MobileScannerController(autoStart: false,
      detectionSpeed: DetectionSpeed.noDuplicates);

[atishoo]

Adding autoStart: false to the controller solved it for me:

final MobileScannerController controller = MobileScannerController(autoStart: false,
      detectionSpeed: DetectionSpeed.noDuplicates);

yes, you are right bro! this way works for me.

[aimeykra]

Does it require to upgrade to a new version of the package? I am using v5.1.1.

[ghost]

Any progress about this issue?

[juliansteenbakker]

I'm closing this as there is no activity, and newer versions of this plug are already released. If this still happens with the latest version let me know by commenting.