149 lines
4.3 KiB
Dart
149 lines
4.3 KiB
Dart
import 'package:flutter/foundation.dart';
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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 AsyncCallback onStartOfPage;
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/// Called when the [child] reaches the end of the list
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final AsyncCallback onEndOfPage;
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/// Called when the list scrolling starts
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final VoidCallback onPageScrollStart;
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/// Called when the list scrolling ends
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final VoidCallback onPageScrollEnd;
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/// Called every time the [child] is in-between the list
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final VoidCallback onInBetweenOfPage;
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/// The offset to take into account when triggering [onEndOfPage]/[onStartOfPage] 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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const 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.onPageScrollStart,
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this.onPageScrollEnd,
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this.onInBetweenOfPage,
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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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double _scrollPosition = 0.0;
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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 ScrollStartNotification) {
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if (widget.onPageScrollStart != null) {
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widget.onPageScrollStart();
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return true;
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}
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}
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if (notification is ScrollEndNotification) {
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if (widget.onPageScrollEnd != null) {
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widget.onPageScrollEnd();
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return true;
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}
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}
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if (notification is ScrollUpdateNotification) {
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final pixels = notification.metrics.pixels;
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final maxScrollExtent = notification.metrics.maxScrollExtent;
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final minScrollExtent = notification.metrics.minScrollExtent;
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final scrollOffset = widget.scrollOffset;
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if (pixels > (minScrollExtent + scrollOffset) &&
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pixels < (maxScrollExtent - scrollOffset)) {
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if (widget.onInBetweenOfPage != null) {
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widget.onInBetweenOfPage();
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return true;
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}
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}
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final extentBefore = notification.metrics.extentBefore;
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final extentAfter = notification.metrics.extentAfter;
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final scrollingDown = _scrollPosition < pixels;
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if (scrollOffset == null || scrollOffset == 0) {
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if (extentAfter == 0) {
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_onEndOfPage();
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}
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if (extentBefore == 0) {
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_onStartOfPage();
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}
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} else {
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if (scrollingDown) {
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if (extentAfter <= scrollOffset) {
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_onEndOfPage();
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}
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} else {
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if (extentBefore <= scrollOffset) {
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_onStartOfPage();
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}
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}
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}
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_scrollPosition = pixels;
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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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_onEndOfPage();
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}
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if (notification.overscroll < 0) {
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_onStartOfPage();
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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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void _onEndOfPage() {
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if (_loadMoreStatus != null && _loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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if (widget.onEndOfPage != null) {
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widget.onEndOfPage().whenComplete(() {
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_loadMoreStatus = _LoadingStatus.STABLE;
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});
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}
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}
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}
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void _onStartOfPage() {
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if (_loadMoreStatus != null && _loadMoreStatus == _LoadingStatus.STABLE) {
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_loadMoreStatus = _LoadingStatus.LOADING;
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if (widget.onStartOfPage != null) {
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widget.onStartOfPage().whenComplete(() {
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_loadMoreStatus = _LoadingStatus.STABLE;
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});
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}
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}
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}
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}
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