Created
September 24, 2021 11:04
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This code snippets provide a delegate to build separators in a SliverList. Original code from https://github.com/BreX900/easy_widget. I rewrote it, so that it's null-safety conform.
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| import 'package:flutter/widgets.dart'; | |
| class SliverLayoutDelegate extends SliverChildBuilderDelegate { | |
| SliverLayoutDelegate({ | |
| bool addAutomaticKeepAlives = true, | |
| bool addRepaintBoundaries = true, | |
| bool addSemanticIndexes = true, | |
| SemanticIndexCallback? semanticIndexCallback, | |
| int semanticIndexOffset = 0, | |
| required int childCount, | |
| bool surround: false, | |
| IndexedWidgetBuilder? separatorBuilder, | |
| required IndexedWidgetBuilder builder, | |
| }) : super( | |
| (separatorBuilder == null | |
| ? builder | |
| : WidgetBuilderUtility.builderWithSeparator( | |
| builder, | |
| separatorBuilder, | |
| surround: surround, | |
| )), | |
| childCount: WidgetBuilderUtility.childCount( | |
| childCount, | |
| separatorBuilder != null, | |
| surround: surround, | |
| ), | |
| addAutomaticKeepAlives: addAutomaticKeepAlives, | |
| addRepaintBoundaries: addRepaintBoundaries, | |
| addSemanticIndexes: addSemanticIndexes, | |
| semanticIndexCallback: (Widget _, int localIndex) => localIndex, | |
| semanticIndexOffset: semanticIndexOffset, | |
| ); | |
| factory SliverLayoutDelegate.childrenBuilder({ | |
| bool addAutomaticKeepAlives = true, | |
| bool addRepaintBoundaries = true, | |
| bool addSemanticIndexes = true, | |
| SemanticIndexCallback? semanticIndexCallback, | |
| int semanticIndexOffset = 0, | |
| bool surround: false, | |
| required int childCount, | |
| required Widget separator, | |
| required IndexedWidgetBuilder builder, | |
| }) { | |
| return SliverLayoutDelegate( | |
| surround: surround, | |
| childCount: childCount, | |
| separatorBuilder: (_, __) => separator, | |
| builder: builder, | |
| addAutomaticKeepAlives: addAutomaticKeepAlives, | |
| addRepaintBoundaries: addRepaintBoundaries, | |
| addSemanticIndexes: addSemanticIndexes, | |
| semanticIndexCallback: (Widget _, int localIndex) => localIndex, | |
| semanticIndexOffset: semanticIndexOffset, | |
| ); | |
| } | |
| factory SliverLayoutDelegate.children({ | |
| bool surround: false, | |
| bool addAutomaticKeepAlives = true, | |
| bool addRepaintBoundaries = true, | |
| bool addSemanticIndexes = true, | |
| SemanticIndexCallback? semanticIndexCallback, | |
| int semanticIndexOffset = 0, | |
| Widget? separator, | |
| required List<Widget> children, | |
| }) { | |
| return SliverLayoutDelegate( | |
| surround: surround, | |
| builder: (context, index) => children[index], | |
| childCount: children.length, | |
| separatorBuilder: | |
| separator == null ? (_, __) => SizedBox() : (_, __) => separator, | |
| addAutomaticKeepAlives: addAutomaticKeepAlives, | |
| addRepaintBoundaries: addRepaintBoundaries, | |
| addSemanticIndexes: addSemanticIndexes, | |
| semanticIndexCallback: (Widget _, int localIndex) => localIndex, | |
| semanticIndexOffset: semanticIndexOffset, | |
| ); | |
| } | |
| } | |
| class ListUtility { | |
| static List<E> joiner<E>(List<E> list, E builder(int index)) { | |
| if (list.length == 1) return list.toList(); | |
| final length = (list.length * 2) - 1; | |
| // ignore: deprecated_member_use | |
| final newList = <E>[]..length = length; | |
| for (int i = 0; i < (list.length - 1); i++) { | |
| final index = i * 2; | |
| newList | |
| ..[index] = list[i] | |
| ..[index + 1] = builder(i); | |
| } | |
| return newList..[length - 1] = list.last; | |
| } | |
| static List<E> nullGenerator<E>(E builder(int index), {int? itemCount}) { | |
| if (itemCount != null) return List.generate(itemCount, builder); | |
| E element = builder(0); | |
| if (element == null) return <E>[]; | |
| List<E> newList = <E>[element]; | |
| for (int i = 1; element != null; i++) { | |
| newList..add(element); | |
| element = builder(i); | |
| } | |
| return newList; | |
| } | |
| } | |
| class WidgetBuilderUtility { | |
| static IndexedWidgetBuilder builderWithSeparator( | |
| IndexedWidgetBuilder builder, IndexedWidgetBuilder separatorBuilder, | |
| {bool surround: false}) { | |
| if (separatorBuilder == null) return builder; | |
| return (context, index) { | |
| final itemIndex = index ~/ 2; | |
| if (surround ? !(index % 2 == 0) : (index % 2 == 0)) | |
| return builder(context, itemIndex); | |
| else | |
| return separatorBuilder(context, itemIndex); | |
| }; | |
| } | |
| static int separatorCount(int childCount, [bool surround = false]) { | |
| return childCount > 0 | |
| ? ((childCount > 1 ? childCount - 1 : 0) + (surround ? 2 : 0)) | |
| : 0; | |
| } | |
| static int childCount(int childCount, bool existSeparator, | |
| {bool surround: false}) { | |
| return childCount + | |
| (existSeparator ? separatorCount(childCount, surround) : 0); | |
| } | |
| } |
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