Flutter - Unable to navigate away/show dialog when snapshot error occurs

Question

I got this simple build function which should show a dialog when the snapshot has an error, but I'm unable to do so without getting the following error:

flutter: The following assertion was thrown building FutureBuilder(dirty, dependencies: flutter: [_LocalizationsScope-[GlobalKey#f4f3f], _InheritedTheme], state: flutter: _FutureBuilderState#175f8): flutter: setState() or markNeedsBuild() called during build. flutter: This Overlay widget cannot be marked as needing to build because the framework is already in the flutter: process of building widgets. A widget can be marked as needing to be built during the build phase flutter: only if one of its ancestors is currently building. This exception is allowed because the framework flutter: builds parent widgets before children, which means a dirty descendant will always be built. flutter: Otherwise, the framework might not visit this widget during this build phase. flutter: The widget on which setState() or markNeedsBuild() was called was: flutter:
Overlay-[LabeledGlobalKey#07fd4]

Code:

showUnknownErrorAlertDialog(BuildContext context, [void Function() onClose]) {

  showDialog(
    context: context,
    builder: (BuildContext builderContext) {

      return AlertDialog(
        title: Text(AppLocalizations.of(builderContext).lang['unknownError']),
        actions: <Widget>[

          FlatButton(
            child: Text(AppLocalizations.of(builderContext).lang['close']),
            onPressed: () {
              Navigator.of(builderContext).pop();

              if (onClose != null) {
                onClose();
              }
            },
          ),
        ],
      );
    }
  );
}

goBack() {
  locator<AppNavigation>().navigateTo('gameOverview', AppGameArgs(gameName));
}

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: getGameSession(),
      builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {

        if (snapshot.hasError) {

          return showUnknownErrorAlertDialog(context, () {
            goBack();
          });
        }
        / ... omitted code .../

How am I supposed to handle errors in the build function if I'm not allowed to show a dialog or navigate away instantly when there's an error?

Guru Prasad mohapatra Guru Prasad mohapatra · Accepted Answer · 2019-12-19T16:53:55

you can't return the dialog directly from the FuturBuilder.You have to use showDialog() to show any dialog and for the click event if you are using navigation in the dialog it'll be used as the navigation of the dialog not the page.

if(snapshot.hasError()){
  showDialog(showUnknownErrorAlertDialog(context, () {
            Navigator.of(context).pop(1);
          })).then((value){
        if(value=null && value==1)
            goBack();
   });
   return Container();
}

you can return value from dialog and check the result and run your goBack() there

Flutter - Unable to navigate away/show dialog when snapshot error occurs

1 Answers