import 'dart:collection'; import 'package:flutter/material.dart'; import 'package:flutter/services.dart'; import 'package:flutter_hooks/flutter_hooks.dart'; import '../hooks/ref.dart'; import 'bottom_safe.dart'; class InfiniteScrollController { late VoidCallback clear; InfiniteScrollController() { usedBeforeCreation() => throw Exception( 'Tried to use $runtimeType before it being initialized'); clear = usedBeforeCreation; } } /// `ListView.builder` with asynchronous data fetching and no `itemCount` class InfiniteScroll extends HookWidget { /// How many items should be fetched per call final int batchSize; /// Widget displayed at the bottom when InfiniteScroll is fetching final Widget loadingWidget; /// Builds your widget from the fetched data final Widget Function(T data) itemBuilder; /// Fetches data to be displayed. It is important to respect `batchSize`, /// if the returned list has less than `batchSize` then the InfiniteScroll /// is considered finished final Future> Function(int page, int batchSize) fetcher; final InfiniteScrollController? controller; /// Widget to be added at the beginning of the list final Widget leading; /// Padding for the [ListView.builder] final EdgeInsetsGeometry? padding; /// Widget that will be displayed if there are no items final Widget noItems; /// Maps an item to its unique property that will allow to detect possible /// duplicates thus perfoming deduplication final Object Function(T item)? uniqueProp; const InfiniteScroll({ this.batchSize = 10, this.leading = const SizedBox.shrink(), this.padding, this.loadingWidget = const ListTile(title: Center(child: CircularProgressIndicator())), required this.itemBuilder, required this.fetcher, this.controller, this.noItems = const SizedBox.shrink(), this.uniqueProp, }) : assert(batchSize > 0); @override Widget build(BuildContext context) { final data = useState>([]); // holds unique props of the data final dataSet = useRef(HashSet()); final hasMore = useRef(true); final page = useRef(1); final isFetching = useRef(false); final uniquePropFunc = uniqueProp ?? (e) => e as Object; useEffect(() { if (controller != null) { controller?.clear = () { data.value = []; hasMore.current = true; page.current = 1; dataSet.current.clear(); }; } return null; }, []); return RefreshIndicator( onRefresh: () async { data.value = []; hasMore.current = true; page.current = 1; dataSet.current.clear(); await HapticFeedback.mediumImpact(); await Future.delayed(const Duration(seconds: 1)); }, child: ListView.builder( padding: padding, // +2 for the loading widget and leading widget itemCount: data.value.length + 2, itemBuilder: (_, i) { if (i == 0) { return leading; } i -= 1; // if we are done but we have no data it means the list is empty if (!hasMore.current && data.value.isEmpty) { return Center(child: noItems); } // reached the bottom, fetch more if (i == data.value.length) { // if there are no more, skip if (!hasMore.current) { return const BottomSafe(); } // if it's already fetching more, skip if (!isFetching.current) { isFetching.current = true; fetcher(page.current, batchSize).then((incoming) { // if got less than the batchSize, mark the list as done if (incoming.length < batchSize) { hasMore.current = false; } final newData = incoming.where( (e) => !dataSet.current.contains(uniquePropFunc(e)), ); // append new data data.value = [...data.value, ...newData]; dataSet.current.addAll(newData.map(uniquePropFunc)); page.current += 1; }).whenComplete(() => isFetching.current = false); } return SafeArea( top: false, child: loadingWidget, ); } // not last element, render list item return itemBuilder(data.value[i]); }, ), ); } }