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

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?

Answer 1

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