Unclear how to use flushbar

[degloff]

I am trying to use flushbar for all kinds of notifications. it works well in general. However I face this error that I do not properly understand. It may well be a wrong usage of flushbar.

Assume I have a widget that gets a list of data. During build I want to notify the user why for example the data is empty (based on his search selection). The simple minded approach is to do something like this (I tried the naviatgor approach because the show method also did not work):

@override
  Widget build(BuildContext context) {
    if (data.isEmpty) {
      var flushbar = FlushbarHelper.createInformation(message: 'No data matching selection criteria.');
      Navigator.push(context, FlushbarRoute(theme: Theme.of(context), flushbar: flushbar));
      return Container(
          height: 100,
          child: Center(
            child: Icon(Icons.crop_square, size: 35),
          )
      );
    } else {
      return GFItemsCarousel(
          rowCount: 2,
          children: data.map((d) {
            return overviewTile(context, d);
          }).toList()
      );
    }
  }

I get the following exception

The following assertion was thrown building FilteredGameCarousel(dirty, dependencies: [MediaQuery, _LocalizationsScope-[GlobalKey#0ea56], _InheritedTheme]):
setState() or markNeedsBuild() called during build.

This Overlay widget cannot be marked as needing to build because the framework is already in the process of building widgets.  A widget can be marked as needing to be built during the build phase only if one of its ancestors is currently building. This exception is allowed because the framework builds parent widgets before children, which means a dirty descendant will always be built. Otherwise, the framework might not visit this widget during this build phase.
The widget on which setState() or markNeedsBuild() was called was: Overlay-[LabeledGlobalKey<OverlayState>#dca70]

What is the cause of that? Is it a wrong usage?

[degloff]

Seems to work if I wrap it with WidgetsBinding.instance.addPostFrameCallback