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(),
 ));
}