flutter form

示例：

import 'package:Flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: FormTestRoute(),
    );
  }
}


class FormTestRoute extends StatefulWidget {
  @override
  _FormTestRouteState createState() => new _FormTestRouteState();
}

class _FormTestRouteState extends State<FormTestRoute> {
  TextEditingController _unameController = TextEditingController();
  TextEditingController _pwdController = TextEditingController();
  GlobalKey _formKey= GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title:Text("Form Test"),
      ),
      body: Padding(
        padding: const EdgeInsets.symmetric(vertical: 16.0, horizontal: 24.0),
        child: Form(
          key: _formKey, //设置globalKey，用于后面获取FormState
          autovalidate: true, //开启自动校验
          child: ListView(
            children: <Widget>[
              TextFormField(
                  autofocus: false,
                  controller: _unameController,
                  decoration: Inputdecoration(
//                      labelText: "用户名",
                      hintText: "用户名或邮箱",
                      icon: Icon(Icons.person)
                  ),
                  // 校验用户名
                  validator: (v) {
                    return v.trim().length > 0 ? null : "用户名不能为空";
                  }

              ),
              TextFormField(
                  controller: _pwdController,
                  keyboardType: TextInputType.numberWithOptions(),
                  decoration: Inputdecoration(
//                      labelText: "密码",
                      hintText: "您的登录密码",
                      icon: Icon(Icons.lock)
                  ),
                  obscureText: true,
                  //校验密码
                  validator: (v) {
                    return v.trim().length > 5 ? null : "密码不能少于6位";
                  }
              ),
              // 登录按钮
              Padding(
                padding: const EdgeInsets.only(top: 28.0),
                child: Row(
                  children: <Widget>[
                    Expanded(
                      child: RaisedButton(
                        padding: EdgeInsets.all(15.0),
                        shape: RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(28))),
                        child: Text("登录"),
                        color: Theme.of(context).primaryColor,
                        textColor: Colors.white,
                        onpressed: () {
                          //在这里不能通过此方式获取FormState，context不对
                          //print(Form.of(context));

                          // 通过_formKey.currentState 获取FormState后，
                          // 调用validate()方法校验用户名密码是否合法，校验
                          // 通过后再提交数据。
                          if((_formKey.currentState as FormState).validate()){
                            //验证通过提交数据
                          }
                        },
                      ),
                    ),
                  ],
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}