page_transition.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      theme: ThemeData(
        pageTransitionsTheme: PageTransitionsTheme(builders: {
          for (var item in TargetPlatform.values) item: _TransitionBuilder(),
        }),
      ),
      routes: {
        for (var i = 0; i < 6; i++)
          '/screen${i + 1}': (context) => Screen(currentScreen: i + 1),
      },
      initialRoute: '/screen1',
    );
  }
}

class Screen extends StatelessWidget {
  const Screen({
    Key? key,
    required this.currentScreen,
  }) : super(key: key);
  final int currentScreen;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: currentScreen == 1
            ? null
            : BackButton(
                onPressed: () {
                  if (currentScreen == 6) {
                    Navigator.of(context)
                        .popUntil(ModalRoute.withName('/screen3'));
                  } else {
                    Navigator.of(context).pop();
                  }
                },
              ),
        title: Text('Screen $currentScreen'),
      ),
      body: currentScreen == 6
          ? null
          : Center(
              child: ElevatedButton(
                onPressed: () {
                  Navigator.of(context)
                      .pushNamed('/screen${currentScreen + 1}');
                },
                child: const Text('Next'),
              ),
            ),
    );
  }
}

class _TransitionBuilder extends PageTransitionsBuilder {
  @override
  Widget buildTransitions<T>(
    PageRoute<T> route,
    BuildContext context,
    Animation<double> animation,
    Animation<double> secondaryAnimation,
    Widget child,
  ) =>
      FadeTransition(opacity: animation, child: child);
}