septemberAppBar

main.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: '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> {
  static const _tileHeight = 40.0;
  static final approximateDaysPerMonth = Iterable<int>.generate(30);
  static const _months = ["August", "September"];
  final controller = ScrollController();
  String _title = "August";

  @override
  void initState() {
    super
        .initState(); // did you know? initState's doc says to call super.initState FIRST in implementers
    controller.addListener(_onScroll);
  }

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

  void _onScroll() {
    final itemIndex = controller.offset ~/ _tileHeight;
    setState(() => _title = _months[itemIndex ~/ 30]);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(_title)),
      body: ListView.builder(
        itemCount: _months.length * approximateDaysPerMonth.length,
        controller: controller,
        itemBuilder: (_, index) {
          final month = _months[index ~/ approximateDaysPerMonth.length];
          final day = index % 30 + 1;
          return SizedBox(
            height: _tileHeight,
            child: ListTile(title: Text('$month $day')),
          );
        },
      ),
    );
  }
}