import 'package:flutter/material.dart';
class RegPage extends StatefulWidget {
  const RegPage({super.key});

  @override
  State createState() => _RegPage();
}

class _RegPage extends State<RegPage> with WidgetsBindingObserver {
  List items = List<ListItem>.generate(
    1000,
    (i) => i % 6 == 0
        ? HeadingItem('Heading $i')
        : MessageItem('Sender $i', i.toString()),
  );

  @override
  void initState() {
    super.initState();
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: null,
      body: ListView.builder(
        primary: false,
        scrollDirection: Axis.vertical,
        shrinkWrap: true,
        itemExtent: 80,
        itemCount: items.length,
        itemBuilder: (context, index) {
          final item = items[index];

          return ListTile(
            title: item.buildTitle(context),
            subtitle: item.buildSubtitle(context),
          );
        },
      ),
    );
  }
}

abstract class ListItem {
  Widget buildTitle(BuildContext context);

  Widget buildSubtitle(BuildContext context);
}

class HeadingItem implements ListItem {
  final String heading;

  HeadingItem(this.heading);

  @override
  Widget buildTitle(BuildContext context) {
    return Text(
      heading,
      style: Theme.of(context).textTheme.headline5,
    );
  }

  @override
  Widget buildSubtitle(BuildContext context) => const SizedBox.shrink();
}

class MessageItem implements ListItem {
  final String sender;
  final String uri;

  MessageItem(this.sender, this.uri);

  @override
  Widget buildTitle(BuildContext context) => Text(sender);

  @override
  Widget buildSubtitle(BuildContext context) =>
      Image.network('https://picsum.photos/250?image=$uri');
}