detects there's no barcode

[jameschristianw]

ondetect runs when there's a barcode. how to tell if there's no barcode?

[navaronbracke]

We could make onDetect return a nullable BarcodeCapture. The barcodes stream does also not report events when an image frame has no barcode I think. (because that would be expensive, you'd have to send events every frame)

I'm curious about your use case, though? How would you handle this with a continuous stream of images frames that all might not contain barcodes?

[jameschristianw]

i agree that would be expensive.
to be fair, i still don't know how to handle the continuous stream of image
so what i'm doing right now is save detected barcode to a temp variable, pausing subscription, do something with the barcode, remove the detecte barcode from temp variable, resume subs

i have a suggestion, i don't know if this is feasible or not, can you add new function to controller to detect current frame

[navaronbracke]

Pausing the subscription when a barcode is received is the correct way to handle things here.

What do you mean with "detect current frame" ? The scanner continuously uses the frames as they come in for detection, so I do not see how that is different from "detect the current frame" ?

[Andrflor]

We could make onDetect return a nullable BarcodeCapture. The barcodes stream does also not report events when an image frame has no barcode I think. (because that would be expensive, you'd have to send events every frame)

I'm curious about your use case, though? How would you handle this with a continuous stream of images frames that all might not contain barcodes?

The thing is that you may want to do continuous detection
For example overlay the barcodes detected with a rectangle and maybe also show some info or action either like android qrcode scanner or with augmented reality of some form.

To do that i use a workaround by adding an empty capture on timeout.

Stream<T> addTimeoutEvent<T>(
    Stream<T> stream, Duration timeout, T timeoutEvent) {
  final StreamController<T> controller = StreamController<T>();

  Timer? timer;
  void resetTimer() {
    timer?.cancel();
    timer = Timer(timeout, () {
      controller.add(timeoutEvent);
      resetTimer();
    });
  }

  stream.listen(
    (T event) {
      resetTimer();
      controller.add(event);
    },
    onError: controller.addError,
    onDone: controller.close,
  );

  return controller.stream;
}

[navaronbracke]

I think we will need to expose this in the plugin itself, as we now have an extra use-case:

In the upcoming version 7.0.0 of the plugin, we provided a widget that draws the barcode shapes on the screen.
However, that widget will need to know when there are no more barcodes in view, to clear the old shapes.