Flutter:在应用程序启动时显示AlertDialog

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter AlertDialog'),
        ),
        body: Center(
          child: RaisedButton(
            child: Text('Show AlertDialog'),
            onPressed: () {
              showDialog(
                context: context,
                builder: (BuildContext context) {
                  return AlertDialog(
                    title: Text('提示'),
                    content: Text('确定要退出应用吗？'),
                    actions: <Widget>[
                      FlatButton(
                        child: Text('取消'),
                        onPressed: () {
                          Navigator.of(context).pop();
                        },
                      ),
                      FlatButton(
                        child: Text('确定'),
                        onPressed: () {
                          // 执行退出应用的操作
                          Navigator.of(context).pop();
                        },
                      ),
                    ],
                  );
                },
              );
            },
          ),
        ),
      ),
    );
  }
}