import 'package:flutter/material.dart';class MyApp extends StatefulWidget { @override _MyApp createState() => new _MyApp();}class _MyApp extends State<MyApp> { String _lastName; String _firstName; GlobalKey<FormState> _formKey = new GlobalKey<FormState>(); void _showMessage(String name) {  showDialog<Null>(   context: context,   child: new AlertDialog(    content: new Text(name),    actions: <Widget>[     new FlatButton(      onPressed: () {       Navigator.pop(context);      },      child: new Text('確定')     )    ]   )  ); } @override Widget build(BuildContext context) {  return new Scaffold(   appBar: new AppBar(    title: new Text('表單輸入')   ),   // Form：用于將多個表單控件組合在一起的容器   body: new Form(    key: _formKey,    child: new Column(     children: <Widget> [      // TextFieldd：包含輸入的表單控件，每個表單字段都應該在FormField控件中      new TextField(       labelText: '姓氏',       // onSaved：當通過Form.save()保存表單時調用的方法       onSaved: (InputValue value) {        _lastName = value.text;       }      ),      new TextField(       labelText: '名字',       onSaved: (InputValue value) {        _firstName = value.text;       }      ),      new Row(       children: <Widget> [        new RaisedButton(         child: new Text('重置'),         onPressed: () {          // reset()：將此Form下的每個TextField重置為初始狀態          _formKey.currentState.reset();          _showMessage('姓名信息已經重置');         }        ),        new RaisedButton(         child: new Text('提交'),         onPressed: () {          // save()：保存Form下的每個TextField          _formKey.currentState.save();          _showMessage('你的姓名是'+_lastName+_firstName);         }        )       ]      )     ]    )   )  ); }}void main() { runApp(new MaterialApp(  title: 'Flutter Demo',  home: new MyApp() ));}