Using State in Dialog

stateful_dialog.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool checked = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              child: Text('Open AlertDialog'),
              onPressed: () {
                showDialog(
                  context: context,
                  builder: (context) {
                    return StatefulBuilder(
                      builder: (context, setState) {
                        return AlertDialog(
                          title: Text("CheckBox"),
                          actions: <Widget>[
                            Row(
                              children: [
                                Row(
                                  children: [
                                    Checkbox(
                                      value: checked,
                                      onChanged: (bool value) {
                                        setState(() {
                                          checked = value;
                                        });
                                      },
                                    ),
                                    Text('Agree'),
                                  ],
                                ),
                                FlatButton(
                                  onPressed: () => Navigator.pop(context),
                                  child: Text("Dismiss"),
                                ),
                              ],
                            ),
                          ],
                        );
                      },
                    );
                  },
                );
              },
            ),
            RaisedButton(
              child: Text('Open SimpleDialog'),
              onPressed: () {
                showDialog(
                  context: context,
                  builder: (BuildContext context) {
                    return CheckBoxAlertDialog();
                  },
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}

class CheckBoxAlertDialog extends StatefulWidget {
  CheckBoxAlertDialog({Key key}) : super(key: key);

  @override
  _CheckBoxAlertDialogState createState() => _CheckBoxAlertDialogState();
}

class _CheckBoxAlertDialogState extends State<CheckBoxAlertDialog> {
  bool checked = false;

  @override
  Widget build(BuildContext context) {
    return AlertDialog(
      title: Text("CheckBox"),
      actions: <Widget>[
        Row(
          children: [
            Row(children: [
              Checkbox(
                value: checked,
                onChanged: (bool value) {
                  setState(() {
                    checked = value;
                  });
                },
              ),
              Text('Agree'),
            ]),
            FlatButton(
              onPressed: () => Navigator.pop(context),
              child: Text("Dismiss"),
            ),
          ],
        ),
      ],
    );
  }
}