99 lines
3.1 KiB
Dart
99 lines
3.1 KiB
Dart
import 'package:flutter/widgets.dart';
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enum _LoadingStatus { LOADING, STABLE }
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/// A widget that wraps a [Widget] and will trigger [onEndOfPage]/[onStartOfPage] when it
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/// reaches the bottom/start of the list
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class LazyLoadScrollView extends StatefulWidget {
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/// The [Widget] that this widget watches for changes on
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final Widget child;
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/// Called when the [child] reaches the start of the list
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final VoidCallback onStartOfPage;
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/// Called when the [child] reaches the end of the list
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final VoidCallback onEndOfPage;
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/// The offset to take into account when triggering [onEndOfPage] in pixels
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final double scrollOffset;
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/// Used to determine if loading of new data has finished. You should use set this if you aren't using a FutureBuilder or StreamBuilder
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final bool isLoading;
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/// Initiates a LazyLoadScrollView widget
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LazyLoadScrollView({
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Key key,
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@required this.child,
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this.onStartOfPage,
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this.onEndOfPage,
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this.isLoading = false,
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this.scrollOffset = 100,
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}) : assert(child != null),
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super(key: key);
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@override
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State<StatefulWidget> createState() => _LazyLoadScrollViewState();
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}
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class _LazyLoadScrollViewState extends State<LazyLoadScrollView> {
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_LoadingStatus _loadMoreStatus = _LoadingStatus.STABLE;
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@override
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void didUpdateWidget(LazyLoadScrollView oldWidget) {
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super.didUpdateWidget(oldWidget);
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if (!widget.isLoading) {
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_loadMoreStatus = _LoadingStatus.STABLE;
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}
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}
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@override
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Widget build(BuildContext context) {
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return NotificationListener(
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child: widget.child,
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onNotification: _onNotification,
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);
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}
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bool _onNotification(Notification notification) {
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if (notification is ScrollUpdateNotification) {
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if (notification.metrics.maxScrollExtent > notification.metrics.pixels &&
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notification.metrics.maxScrollExtent - notification.metrics.pixels <=
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widget.scrollOffset) {
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if (_loadMoreStatus != null &&
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_loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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widget.onEndOfPage();
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}
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}
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if (notification.metrics.minScrollExtent < notification.metrics.pixels &&
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notification.metrics.pixels - notification.metrics.minScrollExtent <=
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widget.scrollOffset) {
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if (_loadMoreStatus != null &&
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_loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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widget.onStartOfPage();
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}
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}
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return true;
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}
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if (notification is OverscrollNotification) {
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if (notification.overscroll > 0) {
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if (_loadMoreStatus != null &&
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_loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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widget.onEndOfPage();
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}
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}
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if (notification.overscroll < 0) {
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if (_loadMoreStatus != null &&
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_loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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widget.onStartOfPage();
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}
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}
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return true;
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}
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return false;
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}
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}
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