How do I have my app change screens based on my user state? - flutter

Question

I am using the ScopedModel pattern, but I am also interested how this same problem is addressed in the similar Provider pattern.
Currently I have a ScopedModel with a bool exposed called loggedIn. When the FirebaseonAuthStateChanged stream changes user log in state, my ScopedModel changes that bool, and calls NotifyListeners. All straight forward stuff.
Now I am confused as to the best way to push or pop routes based on this ScopedModel.
Should all my logged in screens (screens that require a user) have the following code in build method?
WidgetsBinding.instance.addPostFrameCallback((_) {
if (!auth.hasUser)
Navigator.of(context).pushNamedAndRemoveUntil('/entry', (Route<dynamic> route) => });
});
That seems a little excessive to have this code on every single screen. Is there a way I can define this log screen change behaviour somewhere only once?

Answer 1

create a Widget for it ;)
class Validation extends StatefulWidget {
final Function validator;
final Widget child;
const Validation({Key key, this.validator, this.child}) : super(key: key);
#override
_ValidationState createState() => _ValidationState();
}
class _ValidationState extends State<Validation> {
#override
void initState() {
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
widget.validator();
});
super.initState();
}
#override
Widget build(BuildContext context) {
return widget.child;
}
}
now use it everywhere
#override
Widget build(BuildContext context) {
return Validation(
validator: (){
if (!auth.hasUser){
Navigator.of(context).pushNamedAndRemoveUntil('/entry', (Route<dynamic> route) => false);
}
},
child: MyAwesomePage(),
);
}
you can further simplify if the validation is same everywhere or create multiple validation widget according to the validations required,
FOR YOUR CASE
class LoginValidation extends StatefulWidget {
final String routeIfNotLoggedIn;
final Widget child;
const LoginValidation({Key key, this.routeIfNotLoggedIn, this.child}) : super(key: key);
#override
_LoginValidationState createState() => _LoginValidationState();
}
class _LoginValidationState extends State<LoginValidation> {
#override
void initState() {
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
if (!auth.hasUser){
Navigator.of(context).pushNamedAndRemoveUntil(widget.routeIfNotLoggedIn, (Route<dynamic> route) => false);
}
});
super.initState();
}
}
and use it
#override
Widget build(BuildContext context) {
return LoginValidation(
routeIfNotLoggedIn: "/myLoginRoute",
child: MyAwesomePage(),
);
}