如何使用Flutter成功登录和注销Firebase？

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_auth/firebase_auth.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Firebase Login'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              RaisedButton(
                child: Text('Login'),
                onPressed: () {
                  _login();
                },
              ),
              RaisedButton(
                child: Text('Logout'),
                onPressed: () {
                  _logout();
                },
              ),
            ],
          ),
        ),
      ),
    );
  }

  Future<void> _login() async {
    try {
      UserCredential userCredential = await _auth.signInWithEmailAndPassword(
        email: 'example@example.com',
        password: 'password',
      );
      print('User logged in: ${userCredential.user}');
    } catch (e) {
      print('Login failed: $e');
    }
  }

  Future<void> _logout() async {
    await _auth.signOut();
    print('User logged out');
  }
}