Flutter app not initializing Firebase instance - flutter

Question

I am creating a Flutter app that uses Google Authentication in Firebase.
The user can sign in with Google, but I need to keep the user logged in when the user launches the app again.
This is my code for main.dart
import 'package:flutter/material.dart';
import 'login_page.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
final FirebaseAuth _auth = FirebaseAuth.instance;
Future<void> _checkUserStatusGoogle() async {
await Firebase.initializeApp();
_auth
.authStateChanges()
.listen((User user) {
if (user == null) {
print('User is currently signed out!');
} else {
print('User is signed in!');
}
});
}
#override
void initState() {
Firebase.initializeApp().whenComplete(() {
_checkUserStatusGoogle().then((value) {
print('Check done done');
});
});
}
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'Flutter Login',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: LoginPage(),
);
}
}
There is an error when launching the app with this code:
E/flutter (15566): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()
E/flutter (15566): #0 MethodChannelFirebase.app (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:118:5)
E/flutter (15566): #1 Firebase.app (package:firebase_core/src/firebase.dart:52:41)
E/flutter (15566): #2 FirebaseAuth.instance (package:firebase_auth/src/firebase_auth.dart:37:47)
E/flutter (15566): #3 new MyApp (package:flutter_faro_turnos/main.dart:10:43)
E/flutter (15566): #4 main (package:flutter_faro_turnos/main.dart:6:23)
E/flutter (15566): #5 _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:233:25)
E/flutter (15566): #6 _rootRun (dart:async/zone.dart:1190:13)
E/flutter (15566): #7 _CustomZone.run (dart:async/zone.dart:1093:19)
E/flutter (15566): #8 _runZoned (dart:async/zone.dart:1630:10)
E/flutter (15566): #9 runZonedGuarded (dart:async/zone.dart:1618:12)
E/flutter (15566): #10 _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:225:5)
E/flutter (15566): #11 _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
E/flutter (15566): #12 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)
What is wrong in my code?
EDIT:
New main.dart code:
import 'package:flutter/material.dart';
import 'login_page.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
void main() async {
await Firebase.initializeApp();
runApp(MyApp());
}
class MyApp extends StatelessWidget {
final FirebaseAuth _auth = FirebaseAuth.instance;
Future<void> _checkUserStatusGoogle() async {
print('User is currently signed out!');
FirebaseAuth.instance
.authStateChanges()
.listen((User user) {
if (user == null) {
print('User is currently signed out!');
} else {
print('User is signed in!');
}
});
}
#override
void initState() {
print ("estoy en initstate");
Firebase.initializeApp().whenComplete(() {
_checkUserStatusGoogle().then((value) {
print('Check done done');
});
});
}
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'Flutter Login',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: LoginPage(),
);
}
}
New error output:
E/flutter (18393): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized.
E/flutter (18393): If you're running an application and need to access the binary messenger before `runApp()` has been called (for example, during plugin initialization), then you need to explicitly call the `WidgetsFlutterBinding.ensureInitialized()` first.
E/flutter (18393): If you're running a test, you can call the `TestWidgetsFlutterBinding.ensureInitialized()` as the first line in your test's `main()` method to initialize the binding.
E/flutter (18393): #0 defaultBinaryMessenger.<anonymous closure> (package:flutter/src/services/binary_messenger.dart:93:7)
E/flutter (18393): #1 defaultBinaryMessenger (package:flutter/src/services/binary_messenger.dart:106:4)
E/flutter (18393): #2 MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:145:62)
E/flutter (18393): #3 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:151:35)
E/flutter (18393): #4 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:334:12)
E/flutter (18393): #5 MethodChannel.invokeListMethod (package:flutter/src/services/platform_channel.dart:347:40)
E/flutter (18393): #6 MethodChannelFirebase._initializeCore (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:30:36)
E/flutter (18393): #7 MethodChannelFirebase.initializeApp (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:75:13)
E/flutter (18393): #8 Firebase.initializeApp (package:firebase_core/src/firebase.dart:43:25)
E/flutter (18393): #9 main (package:flutter_faro_turnos/main.dart:7:18)
E/flutter (18393): #10 _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:233:25)
E/flutter (18393): #11 _rootRun (dart:async/zone.dart:1190:13)
E/flutter (18393): #12 _CustomZone.run (dart:async/zone.dart:1093:19)
E/flutter (18393): #13 _runZoned (dart:async/zone.dart:1630:10)
E/flutter (18393): #14 runZonedGuarded (dart:async/zone.dart:1618:12)
E/flutter (18393): #15 _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:225:5)
E/flutter (18393): #16 _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:301:19)
E/flutter (18393): #17 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)
E/flutter (18393):
V/FA (18393): Inactivity, disconnecting from the service

Answer 1

This line of code is executing in during the construction of MyApp, before any of its methods are called:
final FirebaseAuth _auth = FirebaseAuth.instance
Since initializeApp() hasn't been invoked yet, this fails and throws the exception. You should consider calling initializeApp() during main instead, as shown here. The post gives several options. Personally, I would use main().
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
runApp(MyApp());
}
You only need the one call to initializeApp() when your app starts, so you should also remove the other calls in your code.