ChangeNotifierProvider isn't listening - flutter

Question

I am attempting to share a ChangeNotifierProvider to my main.dart, however the value never gets updated.
How it works
main.dart uses ChangeNotifierProvider to get an instance of the class Location()
main.dart routes to the location_login.dart page where a string in Location() class is set.
The instance of Location() should update in main.dart but it DOES NOT.
Here is the main.dart
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(
ChangeNotifierProvider<Location>.value( <------ CREATE CHANGENOTIFIERPROVIDER
value: Location(),
child: MyApp(),
),
);
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
Location location = Provider.of<Location>(context, listen: false); <----- LISTEN TO PROVIDER
return MultiProvider(
providers: [
FutureProvider<List<Report>>(
create: (context) =>
Collection<Report>(path: '${location.getLocation}/data/reports') <----- USE PROVIDER STRING IN PATH
.getUsers(),
initialData: [],
),
],
child: MaterialApp(
routes: {
'/': (context) => LocationLogin(),
'/login': (context) => LoginScreen(),
'/home': (context) => HomeScreen(),
},
// Theme
theme: ThemeData(
fontFamily: 'Nunito',
bottomAppBarTheme: BottomAppBarTheme(
color: Colors.black87,
),
// your customizations here
brightness: Brightness.dark,
buttonTheme: ButtonThemeData(),
),
),
);
}
}
Here is the location_login.dart
#override
Widget build(BuildContext context) {
Location location = Provider.of<Location>(context, listen: true);
return Scaffold(
body: TextButton(
child: Text("Submit",
style: GoogleFonts.poppins(
fontSize: 15.sp, color: Colors.white)),
onPressed: () {
location.setLocation('London'); <------- SETTING LOCATION
}),
);
}
}
Here is the location.dart
class Location with ChangeNotifier {
String place = 'none';
String get getLocation => place;
setLocation(String location) {
place = location;
notifyListeners();
}
}
To reiterate, the issue is that when I click the button in the location_login.dart page to set the location to "London"; it does not update the ChangeNotifierProvider with a new instance of the Location() class containing "London". Therefore, I can not update the path in my FurtureProvider. Any ideas of what is going wrong here? I tried to make this as clear as possible but if you don't understand please ask. Thank you

Answer 1

I think you have not consume the ChangeNotifierProvider.
For me below simple implementation work perfectly.
my main.dart file code is as below...
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'providers/app_provider.dart';
import 'providers/favorites_provider.dart';
import 'providers/comments_provider.dart';
import 'providers/home_provider.dart';
import 'providers/details_provider.dart';
import 'providers/gallery_provider.dart';
import 'providers/chat_provider.dart';
import 'ui/splash.dart';
import 'helper/constants.dart';
import 'ui_user/login.dart';
void main() {
runApp(
MultiProvider(
providers: [
ChangeNotifierProvider(create: (_) => AppProvider()),
ChangeNotifierProvider(create: (_) => GalleryProvider()),
ChangeNotifierProvider(create: (_) => CommentsProvider()),
ChangeNotifierProvider(create: (_) => ChatProvider()),
ChangeNotifierProvider(create: (_) => HomeProvider()),
ChangeNotifierProvider(create: (_) => DetailsProvider()),
ChangeNotifierProvider(create: (_) => FavoritesProvider()),
],
child: MyApp(),
),
);
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Consumer<AppProvider>(
builder: (BuildContext context, AppProvider appProvider, Widget child) {
return MaterialApp(
key: appProvider.key,
debugShowCheckedModeBanner: false,
navigatorKey: appProvider.navigatorKey,
title: Constants.appName,
theme: appProvider.theme,
home: appProvider.isLogin == "0" ? LoginPage() : Splash(),
);
},
);
}
}
And my app_provider.dart as below...
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';
import '../helper/constants.dart';
class AppProvider extends ChangeNotifier {
AppProvider() {
checkTheme();
}
String isLogin = "0";
ThemeData theme = Constants.lightTheme;
Key key = UniqueKey();
GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
void setKey(value) {
key = value;
notifyListeners();
}
void setNavigatorKey(value) {
navigatorKey = value;
notifyListeners();
}
void setTheme(value, c) {
theme = value;
SharedPreferences.getInstance().then((prefs) {
prefs.setString("theme", c).then((val) {
SystemChrome.setEnabledSystemUIOverlays(SystemUiOverlay.values);
SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
statusBarColor:
c == "dark" ? Constants.darkPrimary : Constants.lightPrimary,
statusBarIconBrightness:
c == "dark" ? Brightness.light : Brightness.dark,
));
});
});
notifyListeners();
}
ThemeData getTheme(value) {
return theme;
}
Future<ThemeData> checkTheme() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
ThemeData t;
String r =
prefs.getString("theme") == null ? "light" : prefs.getString("theme");
isLogin = prefs.getString("isLogin") == null? "0" : prefs.getString("isLogin");
if (r == "light") {
t = Constants.lightTheme;
setTheme(Constants.lightTheme, "light");
} else {
t = Constants.darkTheme;
setTheme(Constants.darkTheme, "dark");
}
return t;
}
}
This solution is working very well for me. Hope this will help you too...