在flutter中显示登录表单的问题

import 'package:flutter/material.dart';

class LoginForm extends StatefulWidget {
  @override
  _LoginFormState createState() => _LoginFormState();
}

class _LoginFormState extends State<LoginForm> {
  final _formKey = GlobalKey<FormState>();
  String _username = '';
  String _password = '';

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        children: [
          TextFormField(
            decoration: InputDecoration(labelText: 'Username'),
            validator: (value) {
              if (value.isEmpty) {
                return 'Please enter your username';
              }
              return null;
            },
            onSaved: (value) {
              _username = value;
            },
          ),
          TextFormField(
            decoration: InputDecoration(labelText: 'Password'),
            obscureText: true,
            validator: (value) {
              if (value.isEmpty) {
                return 'Please enter your password';
              }
              return null;
            },
            onSaved: (value) {
              _password = value;
            },
          ),
          RaisedButton(
            child: Text('Login'),
            onPressed: () {
              if (_formKey.currentState.validate()) {
                _formKey.currentState.save();
                // 在这里处理登录逻辑
                // 可以调用后端API进行验证
                // 或者使用本地存储验证
                print('Username: $_username');
                print('Password: $_password');
              }
            },
          ),
        ],
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(
        title: Text('Login Form'),
      ),
      body: Center(
        child: LoginForm(),
      ),
    ),
  ));
}