在显示SimpleDialog时候程序报错 No MaterialLocalizations found 没有找到 MaterialLocalizations

 

搜索找到原因 runApp 需要先调用 StatelessWidget 返回一个 MaterialApp实例.

void main() => runApp(MainPage());class MainPage extends StatelessWidget {  @override  Widget build(BuildContext context) {    return MaterialApp(      title: 'Welcome to Flutter',      debugShowCheckedModeBanner: false,      home: HomePage(),    );  }}

 也就是说runApp 直接接受一个 StatefulWidget就会出现这个错误

 

完整代码

import 'package:flutter/material.dart';void main() => runApp(MainPage());class MainPage extends StatelessWidget {  @override  Widget build(BuildContext context) {    return MaterialApp(      title: 'Welcome to Flutter',      debugShowCheckedModeBanner: false,      home: HomePage(),    );  }}class HomePage extends StatefulWidget {  @override  _HomePage createState() {    return _HomePage(title: '简单对话框组件');  }}enum Department { treasury, state }class _HomePage extends State
     
       {  _HomePage({Key key, @required this.title});  final String title;  ThemeData themeData = new ThemeData.light();  Future
      
        _askedToLead() async {    switch (await showDialog
       
        (        context: context,        builder: (BuildContext context) {          return SimpleDialog(            title: const Text('Select assignment'),            children: 
        
         [              SimpleDialogOption(                onPressed: () {                  Navigator.pop(context, Department.treasury);                },                child: const Text('Treasury department'),              ),              SimpleDialogOption(                onPressed: () {                  Navigator.pop(context, Department.state);                },                child: const Text('State department'),              ),            ],          );        })) {      case Department.treasury:        // Let's go.        // ...        break;      case Department.state:        // ...        break;    }  }  @override  Widget build(BuildContext context) {    return new MaterialApp(      title: this.title,      debugShowCheckedModeBanner: false,      home: new Scaffold(        appBar: new AppBar(          title: new Text(this.title),        ),        body: null,        floatingActionButton: FloatingActionButton(          child: Icon(Icons.format_list_numbered),          onPressed: _askedToLead,        ),      ),      theme: themeData,    );  }}