how can i pass a variable to a class and call that variable in any other screen without it being reset - dart

Question

i want to be able to call an empty variable from a class, assign a value to it and make it persistent, anything aside provider e.t.c would be help, i don't want to overhaul the entire app again to do some bloc, provider e.t.c
NB: all screens are stateful widgets
i have tried creating a class with an empty string and passing a value to it from another screen, but this doesn't seem to work
import 'package:cloud_firestore/cloud_firestore.dart';
import 'dart:async';
import 'package:firebase_auth/firebase_auth.dart';
class MethodA {
// id(user, context){
// var name =user.email;
// }
String identity;
MethodA({this.iD});
bool isLoggedIn() {
if (FirebaseAuth.instance.currentUser() != null) {
return true;
} else {
return false;
}
}
Future<void> addUserA( userinfo) async {
//this.iD=id;
Firestore.instance
.collection('user')
.document('furtherinfo').collection(identity).document('Personal Info')
.setData(userdoc)
.catchError((e) {
print(e);
});
}
each time i pass the argument to i.e foo='bar';
and i import that class in another screen, i.e screen 9, foo is automatically set to null, but i would want foo to be bar

Answer 1

I would suggest that you use the Provider since it is the easiest way for me to manage state throughout the app. Flutter starts with one component on top of the widget tree so i would place my provider here.
Example
void main() {runApp(MyApp());}
class MyApp extends StatelessWidget {
MyApp();
#override
Widget build(BuildContext context) {
return MultiProvider(
providers: [
StreamProvider<FirebaseUser>.value(
stream: FirebaseAuth.instance.onAuthStateChanged, // Provider to manage user throughout the app.
),
],
child: MaterialApp(
title: 'My App',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primaryColor: Colors.green,
primarySwatch: Colors.green,
accentColor: Colors.yellow,
),
home: MainPage(),
),
);
}
}
Then in your class you can do the following
class MethodAService with ChangeNotifier {
String _identity = null;
FirebaseUser _user = null;
// constructor with the (new changes )
MethodAService(FirebaseUser user){
this._user = user;
}
get identity => _identity ;
setIdentity(String identity) {
_identity = identity ;
notifyListeners(); // required to notify the widgets of your change
}
}
Then when you want to use it anywhere in your app just do the following in the build method
#override
Widget build(BuildContext context) {
final user = Provider.of<FirebaseUser>(context); // to get the current user
final methodA = Provider.of<MethodAService>(context); // get your service with identity
// now you can set the string using
methodA.setIdentity('new identity');
// or just use it like this
if(methodA.identity.isNotEmpty()){
print(methodA.identity);
}else{
print('Identity is empty');
}
return ChangeNotifierProvider<MethodAService>(
builder: (context) => MethodAService(user), // Your provider to manage your object, sending the Firebase user in
child: loggedIn ? HomePage() : LoginPage(), );
}
References
Provider Package
Fireship 185 Provider
Great Youtube video explaining the code
Update for comment
For getting the user uid you can just do user.uid
Changed code above to fit the

Answer 2

I'm not sure put the whole app in a StreamProvider is the best choice. That means the app will be rebuilt on each stream value.
To make a Widget available on all screens, you need a TransitionBuilder in your MaterialApp.
To avoid the external dependency you can also use an InheritedWidget
signed_user.dart
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
class SignedUser extends InheritedWidget {
final FirebaseUser user;
SignedUser({#required this.user, #required Widget child})
: super(child: child);
#override
bool updateShouldNotify(SignedUser oldWidget) => true;
static SignedUser of(BuildContext context) =>
context.inheritFromWidgetOfExactType(SignedUser);
}
my_transition_builder.dart
class MyTransitionBuilder extends StatefulWidget {
final Widget child;
const MyTransitionBuilder({Key key, this.child}) : super(key: key);
#override
_MyTransitionBuilderState createState() => _MyTransitionBuilderState();
}
class _MyTransitionBuilderState extends State<MyTransitionBuilder> {
StreamBuilder<FirebaseUser> _builder;
#override
void initState() {
super.initState();
_builder = StreamBuilder<FirebaseUser>(
stream: FirebaseAuth.instance.onAuthStateChanged,
builder: (context, snapshot) {
return SignedUser(
child: widget.child,
user: snapshot.data,
);
});
}
#override
Widget build(BuildContext context) {
return _builder;
}
}
main.dart
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
// this will make your inherited widget available on all screens of your app
builder: (context, child) {
return MyTransitionBuilder(child: child);
},
routes: {
'/editAccount': (context) => new EditAccountPage(),
},
theme: ThemeData(
primarySwatch: Colors.green,
),
home: MyHomePage(),
);
}
}
usage in edit_account_page.dart
#override
Widget build(BuildContext context) {
var user = SignedUser.of(context).user;
return Scaffold(
body: FutureBuilder<DocumentSnapshot>(
future: Firestore.instance.document('users/${user.uid}').get(),