A way to update AppBar title based on what ListTile is being occluded https://twitter.com/luke_pighetti/status/1562871407960522755

list_tile_occluded_app_bar.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final scaffoldKey = GlobalKey();
  final appBarKey = GlobalKey();

  final controller = ScrollController();

  var _title = "August";

  @override
  void initState() {
    controller.addListener(_onScroll);
    super.initState();
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  void _onScroll() {
    final appBarBottomCenter =
        appBarKey.currentContext?.findRenderObject()?.paintBounds.bottomCenter;

    if (appBarBottomCenter != null) {
      final result = scaffoldKey.currentContext
          ?.findRenderObject()
          // shhhhhhhh
          // ignore: invalid_use_of_protected_member
          ?.layer
          ?.find<String>(appBarBottomCenter);

      if (result != null) {
        setState(() {
          _title = result;
        });
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      appBar: AppBar(
        key: appBarKey,
        title: Text(_title),
      ),
      body: ListView(
        controller: controller,
        children: [
          for (final month in ["August", "September"])
            for (final day in [
              1,
              2,
              3,
              4,
              5,
              6,
              7,
              8,
              9,
              10,
              11,
              12,
              13,
              14,
              15,
              16,
              17,
              18,
              19,
              20,
              21,
              22,
              23,
              24,
              25,
              26,
              27,
              28,
              29,
              30
            ])
              AnnotatedRegion<String>(
                value: month,
                child: ListTile(
                  title: Text('$month $day'),
                ),
              )
        ],
      ),
    );
  }
}