How to make ListView preserve its scroll when transitioning to another route?

the way i created a "slide-out" animation in the question wasn't correct. in terms of the framework it's called a secondaryAnimation

to create your own secondary animation, you need to use a PageRouteBuilder transitionBuilder property

example can the code below, which produces such animation, and there's no problem with a ListView

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primaryColor: Colors.white),
      initialRoute: '/',
      onGenerateInitialRoutes: (initialRoute) => [createCustomTransition(HomeScreen())],
      onGenerateRoute: (settings) {
        if (settings.name == '1') {
          return createCustomTransition(SomeScreen());
        }
        return createCustomTransition(OtherScreen());
      },
      debugShowCheckedModeBanner: false,
    );
  }
}

/// Will create a custom route transition for you. 
PageRouteBuilder createCustomTransition(Widget screen) {
  return PageRouteBuilder(
    transitionDuration: const Duration(milliseconds: 700),
    reverseTransitionDuration: const Duration(milliseconds: 700),
    pageBuilder: (context, animation, secondaryAnimation) => screen,
    transitionsBuilder: (context, animation, secondaryAnimation, child) {
      
      final slideAnimation = Tween(
        begin: const Offset(1.0, 0.0),
        end: Offset.zero,
      ).animate(CurvedAnimation(
        curve: Curves.easeOutCubic,
        reverseCurve: Curves.easeInCubic,
        parent: animation,
      ));

      final slideOutAnimation = Tween(
        begin: Offset.zero,
        end: const Offset(-0.3, 0.0),
      ).animate(CurvedAnimation(
        curve: Curves.easeOutCubic,
        reverseCurve: Curves.easeInCubic,
        parent: secondaryAnimation,
      ));

      return SlideTransition(
        position: slideAnimation,
        child: SlideTransition(
          position: slideOutAnimation,
          child: child,
        ),
      );
    },
  );
}

class HomeScreen extends StatelessWidget {
  HomeScreen({Key key}) : super(key: key);
  final List<int> list = List.generate(1000, (index) => index);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(
          children: [
            Expanded(
              child: ListView.builder(
                itemCount: list.length,
                itemBuilder: (context, index) => ListTile(
                  title: Center(
                    child: Text(list[index].toString()),
                  )
                ),
              )
            ),
            ElevatedButton(
              child: const Text('go to some screen'),
              onPressed: () {
                Navigator.of(context).pushNamed('1');
              },
            ),
          ],
        ),
      ),
    );
  }
}
class SomeScreen extends StatelessWidget {
  const SomeScreen({Key key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.red,
      appBar: AppBar(),
      body: Center(
        child: ElevatedButton(
          child: const Text('go to other screen'),
          onPressed: () {
            Navigator.of(context).pushNamed('');
          },
        ),
      ),
    );
  }
}

class OtherScreen extends StatelessWidget {
  const OtherScreen({Key key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.blue,
      appBar: AppBar(),
    );
  }
}

according to docs PageRouteBuilder is

A utility class for defining one-off page routes in terms of callbacks.

it's perfrect for general use, but if you are building something more complex, i suggest taking a look at some framework page route animation impementations and different class relationships they have

• widgets/page_transitions_theme.dart - various page route builders
• material/route - android routes implementation
• cupertino/route - cupertion routes implementation

The way I solved this was by saving the offset into a static variable in the page class, and adding the controller into the listview builder. For example

static double _previousScrollOffset = 0;
final ScrollController _controller = new ScrollController(initialScrollOffset: _previousScrollOffset);

And then I save the state whenever I navigate to a new route. e.g.

onTap: () {
_previousScrollOffset = _controller.offset;
Navigator.pushNamed<bool>(
    context, ROUTE_ADD_HOUSING + "/" + housing.uuid);   
},