lemmur-app-android/lib/widgets/infinite_scroll.dart

103 lines
2.7 KiB
Dart

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import '../hooks/ref.dart';
class InfiniteScrollController {
Function() clear;
InfiniteScrollController() {
usedBeforeCreation() => throw Exception(
'Tried to use $runtimeType before it being initialized');
clear = usedBeforeCreation;
}
void dispose() {
clear = null;
}
}
/// `ListView.builder` with asynchronous data fetching
class InfiniteScroll<T> extends HookWidget {
final int batchSize;
final Widget loadingWidget;
final Widget Function(T data) builder;
final Future<List<T>> Function(int page, int batchSize) fetchMore;
final InfiniteScrollController controller;
final Widget prepend;
final EdgeInsetsGeometry padding;
InfiniteScroll({
this.batchSize = 10,
this.prepend = const SizedBox.shrink(),
this.padding,
this.loadingWidget =
const ListTile(title: Center(child: CircularProgressIndicator())),
@required this.builder,
@required this.fetchMore,
this.controller,
}) : assert(builder != null),
assert(fetchMore != null),
assert(batchSize > 0);
@override
Widget build(BuildContext context) {
final data = useState<List<T>>([]);
final hasMore = useRef(true);
final isFetching = useRef(false);
useEffect(() {
if (controller != null) {
controller.clear = () {
data.value = [];
hasMore.current = true;
};
return controller.dispose;
}
return null;
}, []);
final page = data.value.length ~/ batchSize + 1;
return ListView.builder(
padding: padding,
// +2 for the loading widget and prepend widget
itemCount: data.value.length + 2,
itemBuilder: (_, i) {
if (i == 0) {
return prepend;
}
i -= 1;
// reached the bottom, fetch more
if (i == data.value.length) {
// if there are no more, skip
if (!hasMore.current) {
return SizedBox.shrink();
}
// if it's already fetching more, skip
if (!isFetching.current) {
isFetching.current = true;
fetchMore(page, batchSize).then((newData) {
// if got less than the batchSize, mark the list as done
if (newData.length < batchSize) {
hasMore.current = false;
}
// append new data
data.value = [...data.value, ...newData];
}).whenComplete(() => isFetching.current = false);
}
return loadingWidget;
}
// not last element, render list item
return builder(data.value[i]);
},
);
}
}