Flutter质感设计之弹出菜单

import 'package:flutter/material.dart';class MenusDemo extends StatefulWidget { @override _MenusDemoState createState() => new _MenusDemoState();}class _MenusDemoState extends State<MenusDemo> { String _bodyStr = '显示菜单的点击'; @override Widget build(BuildContext context) {  return new Scaffold(   appBar: new AppBar(    title: new Text('菜单演示'),    actions: <Widget> [     new PopupMenuButton<String>(      onSelected: (String value) {       setState(() {        _bodyStr = value;       });      },      itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[       new PopupMenuItem<String>(        value: '选项一的值',        child: new Text('选项一')       ),       new PopupMenuItem<String>(        value: '选项二的值',        child: new Text('选项二')       )      ]     )    ]   ),   body: new Center(    child: new Text(_bodyStr)   )  ); }}void main() { runApp(new MaterialApp(  title: 'Flutter教程',  home: new MenusDemo(), ));}