flutter 写一个登录页面

好的，下面是一个简单的Flutter登录页面的示例：

import 'package:flutter/material.dart';

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Welcome to My App',
              style: TextStyle(fontSize: 24.0),
            ),
            SizedBox(height: 32.0),
            Container(
              padding: EdgeInsets.symmetric(horizontal: 16.0),
              child: TextField(
                controller: _usernameController,
                decoration: InputDecoration(
                  hintText: 'Username',
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(8.0),
                  ),
                ),
              ),
            ),
            SizedBox(height: 16.0),
            Container(
              padding: EdgeInsets.symmetric(horizontal: 16.0),
              child: TextField(
                controller: _passwordController,
                decoration: InputDecoration(
                  hintText: 'Password',
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(8.0),
                  ),
                ),
                obscureText: true,
              ),
            ),
            SizedBox(height: 32.0),
            RaisedButton(
              onPressed: () {
                // Here's where you would handle the login logic
                final String username = _usernameController.text.trim();
                final String password = _passwordController.text.trim();
                print('Username: $username');
                print('Password: $password');
              },
              child: Text('Log In'),
            ),
          ],
        ),
      ),
    );
  }
}

该页面包含一个具有用于键入用户名和密码的文本字段的表单，以及一个登录按钮。当用户点击登录按钮时，您可以在`onPressed`方法中处理登录逻辑，并检查用户名和密码是否正确，或者在后端执行实际的身份验证操作。在此示例中，我们只是将用户名和密码打印到控制台上。