loris/lib/pages/timeline/timeline.dart

import 'package:flutter/material.dart';
import 'package:localization/localization.dart';
import 'package:loris/partials/thread.dart';
import '../../business_logic/timeline/timeline.dart' as tl;

class Timeline extends StatefulWidget {
  const Timeline({Key? key}) : super(key: key);
  @override
  State<Timeline> createState() => _TimelineState();
}

class _TimelineState extends State<Timeline>
    with AutomaticKeepAliveClientMixin {
  String? oldestId;
  final controller = ScrollController();
  List<Widget> children = [];
  bool loading = false;

  @override
  void initState() {
    super.initState();
    children.add(const LoadingBox());
    fetchMore();
    controller.addListener(() {
      if (controller.position.maxScrollExtent <=
              controller.offset + 2 * MediaQuery.of(context).size.height &&
          !loading) {
        fetchMore();
      }
    });
  }

  Future fetchMore() async {
    while (loading) {
      await Future.delayed(const Duration(milliseconds: 500));
    }
    loading = true;

    final models = await tl.getTimelineFromServer(oldestId);
    setState(() {
      children.removeWhere((element) {
        return element.runtimeType != Thread;
      });

      List<Thread> threads = [];
      for (int i = 0; i < models.length; i++) {
        threads.add(Thread(model: models[i]));
      }

      oldestId = models.last.posts.last.id;

      children.addAll(threads);
      children.add(
        Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TextButton.icon(
              onPressed: () {
                fetchMore();
              },
              icon: const Icon(Icons.more_horiz),
              label: Text("load-more".i18n()),
            )
          ],
        ),
      );
      children.add(const LoadingBox());
      loading = false;
    });
  }

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

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return ListView.separated(
      physics: const AlwaysScrollableScrollPhysics(),
      controller: controller,
      itemBuilder: (context, index) {
        return children[index];
      },
      separatorBuilder: (context, index) {
        return const Divider(
          color: Colors.transparent,
        );
      },
      itemCount: children.length,
      padding: const EdgeInsets.fromLTRB(24, 0, 24, 64),
      addAutomaticKeepAlives: false,
    );
  }

  @override
  bool get wantKeepAlive => true;
}

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

  @override
  Widget build(BuildContext context) {
    return SizedBox.fromSize(
        size: Size(double.infinity, MediaQuery.of(context).size.height),
        child: Center(
          child: SizedBox.fromSize(
            size: const Size(128, 128),
            child: const CircularProgressIndicator(),
          ),
        ));
  }
}