flutter/examples/api/lib/widgets/pop_scope/pop_scope.0.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This sample demonstrates showing a confirmation dialog before navigating
// away from a page.

import 'package:flutter/material.dart';

void main() => runApp(const NavigatorPopHandlerApp());

class NavigatorPopHandlerApp extends StatelessWidget {
  const NavigatorPopHandlerApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      initialRoute: '/home',
      routes: <String, WidgetBuilder>{
        '/home': (BuildContext context) => const _HomePage(),
        '/two': (BuildContext context) => const _PageTwo(),
      },
    );
  }
}

class _HomePage extends StatefulWidget {
  const _HomePage();

  @override
  State<_HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<_HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('Page One'),
            TextButton(
              onPressed: () {
                Navigator.of(context).pushNamed('/two');
              },
              child: const Text('Next page'),
            ),
          ],
        ),
      ),
    );
  }
}

class _PageTwo extends StatefulWidget {
  const _PageTwo();

  @override
  State<_PageTwo> createState() => _PageTwoState();
}

class _PageTwoState extends State<_PageTwo> {
  /// Shows a dialog and resolves to true when the user has indicated that they
  /// want to pop.
  ///
  /// A return value of null indicates a desire not to pop, such as when the
  /// user has dismissed the modal without tapping a button.
  Future<bool?> _showBackDialog() {
    return showDialog<bool>(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: const Text('Are you sure?'),
          content: const Text('Are you sure you want to leave this page?'),
          actions: <Widget>[
            TextButton(
              style: TextButton.styleFrom(textStyle: Theme.of(context).textTheme.labelLarge),
              child: const Text('Nevermind'),
              onPressed: () {
                Navigator.pop(context, false);
              },
            ),
            TextButton(
              style: TextButton.styleFrom(textStyle: Theme.of(context).textTheme.labelLarge),
              child: const Text('Leave'),
              onPressed: () {
                Navigator.pop(context, true);
              },
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('Page Two'),
            PopScope<Object?>(
              canPop: false,
              onPopInvokedWithResult: (bool didPop, Object? result) async {
                if (didPop) {
                  return;
                }
                final bool shouldPop = await _showBackDialog() ?? false;
                if (context.mounted && shouldPop) {
                  Navigator.pop(context);
                }
              },
              child: TextButton(
                onPressed: () async {
                  final bool shouldPop = await _showBackDialog() ?? false;
                  if (context.mounted && shouldPop) {
                    Navigator.pop(context);
                  }
                },
                child: const Text('Go back'),
              ),
            ),
          ],
        ),
      ),
    );
  }
}