example.dart

import 'package:flutter/material.dart';

class AppState extends ChangeNotifier {
  final _pages = ['Page 1', 'Page 2'];

  List<String> get pages => _pages;

  bool get canPop => _pages.length > 1;
  bool get canPush => _pages.length < 5;

  void pop() {
    _pages.removeLast();
    notifyListeners();
  }

  void push() {
    _pages.add('Page ${_pages.length + 1}');
    notifyListeners();
  }
}

final appState = AppState();

void main() {
  final app = MaterialApp(
    builder: (context, _) {
      return AnimatedBuilder(
        animation: appState,
        builder: (context, _) {
          return _buildNavigator();
        },
      );
    },
  );

  runApp(app);
}

Navigator _buildNavigator() {
  return Navigator(
    onPopPage: _popPage,
    pages: appState.pages.map(_buildPage).toList(),
  );
}

bool _popPage(Route<dynamic> route, dynamic result) {
  final success = route.didPop(result);
  if (success) {
    appState.pages.removeLast();
  }
  return success;
}

CustomBuilderPage _buildPage(String title) {
  return CustomBuilderPage<void>(
    key: ValueKey(title),
    routeBuilder: (context, settings) {
      return MaterialPageRoute(
        settings: settings,
        builder: (context) {
          return MyPage(title: title);
        },
      );
    },
  );
}

class MyPage extends StatelessWidget {
  final String title;

  const MyPage({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            RaisedButton(
              child: Text('Pop'),
              onPressed: appState.canPop ? appState.pop : null,
            ),
            RaisedButton(
              child: Text('Push'),
              onPressed: appState.canPush ? appState.push : null,
            ),
          ],
        ),
      ),
    );
  }
}