Flutter10.Form

ex:

import 'package:flutter/material.dart';

void main() => runApp(LoginPage());

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

class _LoginPageState extends State<LoginPage> {
  GlobalKey<FormState> _loginKey = GlobalKey<FormState>();
  String _userName;
  String _password;

  void _login() {
    var _loginForm = _loginKey.currentState;
    if (_loginForm.validate()) {
      _loginForm.save();
      print('name: $_userName, password: $_password');
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                padding: const EdgeInsets.all(10.0),
                child: Form(
                    key: _loginKey,
                    child: Column(
                      children: <Widget>[
                        TextFormField(
                          decoration: InputDecoration(
                            labelText: '请输入用户名',
                          ),
                          onSaved: (value) {
                            print('onSaved :$value');
                            _userName = value;
                          },
                          onFieldSubmitted: (value) {
                            print('onFieldSubmitted : $value');
                          },
                        ),
                        TextFormField(
                          decoration: InputDecoration(
                            labelText: '请输入密码',
                          ),
                          obscureText: true,
                          onSaved: (value) {
                            _password = value;
                          },
                          validator: (value) {
                            return value.length < 6 ? '密码长度不够6位' : null;
                          },
                        ),
                        Container(
                          margin: const EdgeInsets.only(top: 20.0),
                          width: 400.0,
                          height: 40.0,
                          child: RaisedButton(
                            onPressed: () {
                              _login();
                            },
                            child: Text('登录'),
                          ),
                        ),
                      ],
                    )),
              )
            ],
          ),
        ),
      ),
    );
  }
}

输出：