Dialog example for returning data from the dialog.

change_theme_dialog.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ThemeMode themeMode = ThemeMode.light;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      themeMode: themeMode,
      theme: ThemeData.light(),
      darkTheme: ThemeData.dark(),
      home: DialogExample(
        onThemeModeChange: (ThemeMode mode) {
          setState(() {
            themeMode = mode;
          });
        },
      ),
    );
  }
}

class DialogExample extends StatelessWidget {
  const DialogExample({super.key, required this.onThemeModeChange});

  final Function(ThemeMode mode) onThemeModeChange;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FilledButton(
          onPressed: () => _dialogBuilder(context),
          child: const Text('Set theme mode!'),
        ),
      ),
    );
  }

  Future<void> _dialogBuilder(BuildContext context) async {
    final result = await showDialog<ThemeMode>(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          content: Text('What mode do you want to set?'),
          actions: [
            TextButton(
              onPressed: () {
                /// return the false value in the pop
                Navigator.of(context).pop(ThemeMode.light);
              },
              child: Text('Light'),
            ),
            TextButton(
              onPressed: () {
                /// return the true value in the pop
                Navigator.of(context).pop(ThemeMode.dark);
              },
              child: Text('Dark'),
            )
          ],
        );
      },
    );
    if (result != null) {
      onThemeModeChange(result);
    }
  }
}