Flutter + Firebase -检查用户状态

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

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: StreamBuilder<User>(
          stream: _auth.authStateChanges(),
          builder: (context, snapshot) {
            if (snapshot.connectionState == ConnectionState.active) {
              User user = snapshot.data;
              if (user == null) {
                // 用户未登录
                return Text('用户未登录');
              } else {
                // 用户已登录
                return Text('用户已登录：${user.email}');
              }
            } else {
              // 连接状态未知
              return CircularProgressIndicator();
            }
          },
        ),
      ),
    );
  }
}