FirebaseAuthでのログイン機能実装した時のビルドエラー

[![](https://i.stack.imgur.com/qEA1b.png)](https://i.stack.imgur.com/qEA1b.png)

ログイン画面のコード（signup.dart)

```

    import 'package:flutter/cupertino.dart';
    import 'package:flutter/material.dart';
    import 'package:provider/provider.dart';
    import 'login_page.dart';
    import 'signup_model.dart';
    
    class SignupPage extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        final mailController = TextEditingController();
        final passwordController = TextEditingController();
    
        return ChangeNotifierProvider<SignUpModel>(
          create: (_) => SignUpModel(),
          child: Scaffold(
            backgroundColor: Colors.white,
            body: Consumer<SignUpModel>(
              builder: (context, model, child) {
                return SafeArea(
                  child: Container(
                    padding: EdgeInsets.only(left: 16, right: 16),
                    child: Column(
                      mainAxisAlignment: MainAxisAlignment.spaceBetween,
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: <Widget>[
                        Column(
                          crossAxisAlignment: CrossAxisAlignment.start,
                          children: <Widget>[
                            SizedBox(
                              height: 50,
                            ),
                            Text(
                              "Create Account,",
                              style: TextStyle(
                                  fontSize: 26, fontWeight: FontWeight.bold),
                            ),
                            SizedBox(
                              height: 6,
                            ),
                            Text(
                              "Sign up to get started!",
                              style: TextStyle(
                                  fontSize: 20, color: Colors.grey.shade400),
                            ),
                          ],
                        ),
                        Column(
                          children: <Widget>[
                            TextField(
                              controller: mailController,
                              obscureText: true,
                              onChanged: (text) {
                                model.mail = text;
                              },
                              decoration: InputDecoration(
                                labelText: "Email ID",
                                labelStyle: TextStyle(
                                    fontSize: 14,
                                    color: Colors.grey.shade400,
                                    fontWeight: FontWeight.w600),
                                enabledBorder: OutlineInputBorder(
                                  borderRadius: BorderRadius.circular(10),
                                  borderSide:
                                      BorderSide(color: Colors.grey.shade300),
                                ),
                                focusedBorder: OutlineInputBorder(
                                  borderRadius: BorderRadius.circular(10),
                                ),
                                floatingLabelBehavior: FloatingLabelBehavior.auto,
                              ),
                            ),
                            SizedBox(
                              height: 16,
                            ),
                            TextField(
                              controller: passwordController,
                              obscureText: true,
                              onChanged: (text) {
                                model.password = text;
                              },
                              decoration: InputDecoration(
                                labelText: "Password",
                                labelStyle: TextStyle(
                                    fontSize: 14,
                                    color: Colors.grey.shade400,
                                    fontWeight: FontWeight.w600),
                                enabledBorder: OutlineInputBorder(
                                  borderRadius: BorderRadius.circular(10),
                                  borderSide:
                                      BorderSide(color: Colors.grey.shade300),
                                ),
                                focusedBorder: OutlineInputBorder(
                                  borderRadius: BorderRadius.circular(10),
                                ),
                                floatingLabelBehavior: FloatingLabelBehavior.auto,
                              ),
                            ),
                            SizedBox(
                              height: 30,
                            ),
                            Container(
                              height: 50,
                              child: FlatButton(
                                color: Colors.yellow[700],
                                onPressed: () async {
                                  try {
                                    await model.signUp();
    
                                  } catch (e) {
                                  }
                                },
                                padding: EdgeInsets.all(0),
                                shape: RoundedRectangleBorder(
                                  borderRadius: BorderRadius.circular(6),
                                ),
                                child: Ink(
                                  decoration: BoxDecoration(),
                                  child: Container(
                                    alignment: Alignment.center,
                                    constraints: BoxConstraints(
                                        minHeight: 50, maxWidth: double.infinity),
                                    child: Text(
                                      "Sign up",
                                      style: TextStyle(
                                          fontWeight: FontWeight.bold,
                                          color: Colors.white),
                                      textAlign: TextAlign.center,
                                    ),
                                  ),
                                ),
                              ),
                            ),
                            SizedBox(
                              height: 16,
                            ),
                            SizedBox(
                              height: 30,
                            ),
                          ],
                        ),
                        Padding(
                          padding: const EdgeInsets.only(bottom: 10),
                          child: Row(
                            mainAxisAlignment: MainAxisAlignment.center,
                            children: <Widget>[
                              Text(
                                "すでにアカウントをお持ちですか？",
                                style: TextStyle(fontWeight: FontWeight.bold),
                              ),
                              GestureDetector(
                                onTap: () {
                                  Navigator.push(
                                    context,
                                    MaterialPageRoute(
                                      builder: (context) => LoginPage(),
                                    ),
                                  );
                                },
                                child: Text(
                                  "login",
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    color: Color(0xFF3b5999),
                                  ),
                                ),
                              )
                            ],
                          ),
                        )
                      ],
                    ),
                  ),
                );
              },
            ),
          ),
        );
      }
    }
    
```

モデルページ（signup_model.dart）

```

    import 'package:cloud_firestore/cloud_firestore.dart';
    import 'package:firebase_auth/firebase_auth.dart';
    import 'package:flutter/material.dart';
    
    class SignUpModel extends ChangeNotifier {
      String mail = '';
      String password = '';
    
      final FirebaseAuth _auth = FirebaseAuth.instance;
    
      Future signUp() async {
        if (mail.isEmpty) {
          throw ('メールアドレスを入力してください');
        }
    
        if (password.isEmpty) {
          throw ('パスワードを入力してください');
        }
    
        // todo
        final User user = (await _auth.createUserWithEmailAndPassword(
          email: mail,
          password: password,
        ))
            .user!;
        final email = user.email;
    
        FirebaseFirestore.instance.collection('users').add(
          {
            'email': email,
            'createdAt': Timestamp.now(),
          },
        );
      }
    }
    
```
CC BY-SA 4.0
2021-05-18T03:46:08.043
75910
2021-05-26T00:23:35.547
2021-05-18T04:54:29.060
3060
45365
question
ios firebase flutter dart
flutter firebaseをつかってログイン機能をつけたがビルド時にエラーが出てしまいます。
> final FirebaseAuth _auth = FirebaseAuth.instance;

アプリ起動時に Firebase.initialize; はされていますか？？  
<https://firebase.flutter.dev/docs/overview>

```

    import 'package:flutter/material.dart';
    
    // Import the firebase_core plugin
    import 'package:firebase_core/firebase_core.dart';
    
    void main() {
      WidgetsFlutterBinding.ensureInitialized();
      runApp(App());
    }
    
    /// We are using a StatefulWidget such that we only create the [Future] once,
    /// no matter how many times our widget rebuild.
    /// If we used a [StatelessWidget], in the event where [App] is rebuilt, that
    /// would re-initialize FlutterFire and make our application re-enter loading state,
    /// which is undesired.
    class App extends StatefulWidget {
      // Create the initialization Future outside of `build`:
      @override
      _AppState createState() => _AppState();
    }
    
    class _AppState extends State<App> {
      /// The future is part of the state of our widget. We should not call `initializeApp`
      /// directly inside [build].
      final Future<FirebaseApp> _initialization = Firebase.initializeApp();
    
      @override
      Widget build(BuildContext context) {
        return FutureBuilder(
          // Initialize FlutterFire:
          future: _initialization,
          builder: (context, snapshot) {
            // Check for errors
            if (snapshot.hasError) {
              return SomethingWentWrong();
            }
    
            // Once complete, show your application
            if (snapshot.connectionState == ConnectionState.done) {
              return MyAwesomeApp();
            }
    
            // Otherwise, show something whilst waiting for initialization to complete
            return Loading();
          },
        );
      }
    }
    
```
CC BY-SA 4.0
2021-05-26T00:23:35.547
76064
2021-05-26T00:23:35.547
45153
75910
answer