Updating PopScope based on inner Navigator

main.dart

// MIT License
//
// Copyright (c) 2022 Fré Dumazy & Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Builder(
        builder: (context) {
          return Scaffold(
            appBar: AppBar(title: const Text('Home')),
            body: Center(
              child: ElevatedButton(
                onPressed: () => Navigator.of(context).push(
                  MaterialPageRoute(
                    builder: (_) => const NestedNavScreen(),
                  ),
                ),
                child: const Text('Open top level'),
              ),
            ),
          );
        },
      ),
    );
  }
}

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

  static void navigateToIndex(BuildContext context, int index) {
    context
        .findAncestorStateOfType<_NestedNavScreenState>()!
        .navigateToIndex(index);
  }

  static void pop(BuildContext context) {
    context.findAncestorStateOfType<_NestedNavScreenState>()!.pop();
  }

  @override
  State<NestedNavScreen> createState() => _NestedNavScreenState();
}

class _NestedNavScreenState extends State<NestedNavScreen> {
  var _pages = <NestedPage>[
    NestedPage(index: 1),
  ];

  void navigateToIndex(int index) {
    setState(() {
      _pages = List.of(_pages) //
        ..add(NestedPage(index: index));
    });
  }

  void pop() {
    setState(() {
      _pages = List.of(_pages) //
        ..removeLast();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Nested Nav screen')),
      body: PopScope(
        canPop: _pages.length == 1,
        onPopInvokedWithResult: (didPop, _) {
          if (didPop) {
            return;
          } else {
            pop();
          }
        },
        child: Navigator(
          onDidRemovePage: (page) {
            _pages.remove(page);
          },
          pages: _pages,
        ),
      ),
    );
  }
}

class NestedPage extends MaterialPage {
  const NestedPage._({
    required this.index,
    required super.name,
    required super.child,
  });

  factory NestedPage({
    required int index,
  }) {
    return NestedPage._(
      index: index,
      name: '$index',
      child: NestedScreen(index: index),
    );
  }

  final int index;
}

class NestedScreen extends StatelessWidget {
  const NestedScreen({super.key, required this.index});

  final int index;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          Text('Nested page: $index'),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              if (Navigator.of(context).canPop())
                ElevatedButton(
                  onPressed: () {
                    NestedNavScreen.pop(context);
                  },
                  child: const Text('Go back'),
                ),
              ElevatedButton(
                onPressed: () {
                  NestedNavScreen.navigateToIndex(context, index + 1);
                },
                child: const Text('Open next'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}