06_Flutter自定义锚点分类列表

2024-05-01 01:44
文章标签 自定义 分类 列表 flutter 06 锚点

本文主要是介绍06_Flutter自定义锚点分类列表，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

06_Flutter自定义锚点分类列表

在这里插入图片描述

这样的效果，大家在一些商超应用里，应该也看到过。接下来咱们就用Flutter一步一步的来实现。

一.自定义属性抽取

在这里插入图片描述

  • categoryWidth: 左侧边栏的宽度，右侧区域的宽度填充剩余空间即可。
  • itemCount: 总共有多少个分类项，也就是左侧边栏中有多少个字项。
  • sticky: 滑动过程中，右侧标题是否吸顶。
  • controller: 外部通过controller可以控制左侧边栏中子项的选中以及右侧列表滑动位置的联动，同时监听选中状态。
  • categoryItemBuilder: 创建左侧边栏中的每一个分类项。
  • sectionItemBuilder: 创建右侧滑动列表中的每一个标题项。
  • sectionOfChildrenBuilder: 创建右侧滑动列表中的每一个标题项对应的子列表
class AnchorCategoryController extends ChangeNotifier {int selectedIndex = 0;void selectTo(int value) {selectedIndex = value;notifyListeners();}@overridevoid dispose() {selectedIndex = 0;super.dispose();}
}class _HomePageState extends State<HomePage> {final List<String> _sections = ["标题1", "标题2", "标题3", "标题4", "标题5", "标题6", "标题7", "标题8", "标题9", "标题10"];final List<List<String>> _childrenList = [["item1", "item2", "item3", "item4", "item5"],["item1", "item2", "item3"],["item1", "item2", "item3", "item4"],["item1"],["item1", "item2"],["item1", "item2", "item3", "item4", "item5", "item6"],["item1", "item2", "item3", "item4"],["item1", "item2", "item3", "item4", "item5"],["item1", "item2", "item3"],["item1", "item2", "item3", "item4", "item5"]];int _selectedSectionsIndex = 0;final AnchorCategoryController _controller = AnchorCategoryController();@overridevoid initState() {super.initState();_controller.addListener(_onCategoryChanged);}void _onCategoryChanged() {setState(() {_selectedSectionsIndex = _controller.selectedIndex;});}@overridevoid dispose() {_controller.removeListener(_onCategoryChanged);_controller.dispose();super.dispose();}@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(widget.title),),body: SafeArea(child: AnchorCategoryList(controller: _controller,itemCount: _sections.length,sticky: true,categoryItemBuilder: (BuildContext context, int index) {return AlphaButton(onTap: () {_controller.selectTo(index);},child: Container(padding: const EdgeInsets.all(10),color: _selectedSectionsIndex == index ? const Color(0xFFFFFFFF): const Color(0xFFF2F2F2),child: Text(_sections[index]),),);},sectionItemBuilder: (BuildContext context, int index) {return Container(padding: const EdgeInsets.symmetric(vertical: 10),alignment: Alignment.centerLeft,color: const Color(0xFFF2F2F2),child: Text(_sections[index]),);},sectionOfChildrenBuilder: (BuildContext context, int index) {return List<Widget>.generate(_childrenList[index].length, (childIndex) {return Container(padding: const EdgeInsets.symmetric(vertical: 10),alignment: Alignment.centerLeft,child: Text(_childrenList[index][childIndex]),);});},)));}
}
二.组件基本布局
class AnchorCategoryList extends StatefulWidget {final double categoryWidth;final int itemCount;final IndexedWidgetBuilder categoryItemBuilder;final IndexedWidgetBuilder sectionItemBuilder;final IndexedWidgetListBuilder sectionOfChildrenBuilder;final bool sticky;final AnchorCategoryController? controller;const AnchorCategoryList({super.key,required this.categoryItemBuilder,required this.sectionItemBuilder,required this.sectionOfChildrenBuilder,this.controller,double? categoryWidth,int? itemCount,bool? sticky}): categoryWidth = categoryWidth ?? 112,itemCount = itemCount ?? 0,sticky = sticky ?? true;@overrideState<StatefulWidget> createState() => _AnchorCategoryListState();}class _AnchorCategoryListState extends State<AnchorCategoryList> {@overrideWidget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [SizedBox(width: widget.categoryWidth,child: LayoutBuilder(builder: (context, viewportConstraints) {return SingleChildScrollView(child: ConstrainedBox(constraints: BoxConstraints(minHeight: viewportConstraints.maxHeight != double.infinity ? viewportConstraints.maxHeight:0),child: Column(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: List.generate(widget.itemCount, (index) {return widget.categoryItemBuilder.call(context, index);}),),),);},)),Expanded(child: CustomScrollView(physics: const ClampingScrollPhysics(),slivers: [...(List<Widget>.generate(widget.itemCount * 2, (allIndex) {int index = allIndex ~/ 2;if(allIndex.isEven) {//sectionreturn SliverToBoxAdapter(child: widget.sectionItemBuilder.call(context, index),);} else {//childrenreturn SliverToBoxAdapter(child: Column(children: widget.sectionOfChildrenBuilder.call(context, index),),);}})),]))],);}}
三.获取并保存标题项、标题项对应子列表的高度

这里获取标题项、标题项对应子列表的高度，需要等到控件build完成后，才能获取到，因此需要自定义一个控件继承SingleChildRenderObjectWidget，并指定一个自定义的RenderBox，在performLayout中通过回调通知外部，控件layout完成了

typedef AfterLayoutCallback = Function(RenderBox ral);class AfterLayout extends SingleChildRenderObjectWidget {final AfterLayoutCallback callback;const AfterLayout({Key? key,required this.callback,Widget? child,}) : super(key: key, child: child);@overrideRenderObject createRenderObject(BuildContext context) {return RenderAfterLayout(callback);}@overridevoid updateRenderObject(context, RenderAfterLayout renderObject) {renderObject.callback = callback;}
}class RenderAfterLayout extends RenderProxyBox {AfterLayoutCallback callback;RenderAfterLayout(this.callback);@overridevoid performLayout() {super.performLayout();SchedulerBinding.instance.addPostFrameCallback((timeStamp) => callback(this));}}

使用AfterLayout获取并保存标题项、标题项对应子列表的高度

@override
Widget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [SizedBox(width: widget.categoryWidth,child: LayoutBuilder(builder: (context, viewportConstraints) {return SingleChildScrollView(child: ConstrainedBox(constraints: BoxConstraints(minHeight: viewportConstraints.maxHeight != double.infinity ? viewportConstraints.maxHeight:0),child: Column(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: List.generate(widget.itemCount, (index) {return widget.categoryItemBuilder.call(context, index);}),),),);},)),Expanded(child: CustomScrollView(physics: const ClampingScrollPhysics(),slivers: [...(List<Widget>.generate(widget.itemCount * 2, (allIndex) {int index = allIndex ~/ 2;if(allIndex.isEven) {//sectionreturn SliverToBoxAdapter(child: AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_sectionHeightList.length > index) {_sectionHeightList[index] = height;} else {_sectionHeightList.add(height);}});},child: widget.sectionItemBuilder.call(context, index),),);} else {//childrenreturn SliverToBoxAdapter(child: AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_childrenHeightList.length > index) {_childrenHeightList[index] = height;} else {_childrenHeightList.add(height);}});},child: Column(children: widget.sectionOfChildrenBuilder.call(context, index),),),);}})),]))],);
}

计算并保存右侧面板每一项选中时的初始滑动偏移量

在这里插入图片描述

@override
Widget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [SizedBox(width: widget.categoryWidth,child: LayoutBuilder(builder: (context, viewportConstraints) {return SingleChildScrollView(child: ConstrainedBox(constraints: BoxConstraints(minHeight: viewportConstraints.maxHeight != double.infinity ? viewportConstraints.maxHeight:0),child: Column(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: List.generate(widget.itemCount, (index) {return widget.categoryItemBuilder.call(context, index);}),),),);},)),Expanded(child: AfterLayout(callback: (renderBox) {setState(() {for(int i = 0; i < widget.itemCount; i ++) {double scrollOffset = 0;for(int j=0; j<i; j++) {scrollOffset += _sectionHeightList[j] + _childrenHeightList[j];}if(_scrollOffsetList.length > i) {_scrollOffsetList[i] = scrollOffset;} else {_scrollOffsetList.add(scrollOffset);}}debugPrint("CustomScrollView AfterLayout: $_scrollOffsetList");});},child: CustomScrollView(physics: const ClampingScrollPhysics(),slivers: [...(List<Widget>.generate(widget.itemCount * 2, (allIndex) {int index = allIndex ~/ 2;if(allIndex.isEven) {//sectionreturn SliverToBoxAdapter(child: AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_sectionHeightList.length > index) {_sectionHeightList[index] = height;} else {_sectionHeightList.add(height);}});},child: widget.sectionItemBuilder.call(context, index),),);} else {//childrenreturn SliverToBoxAdapter(child: AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_childrenHeightList.length > index) {_childrenHeightList[index] = height;} else {_childrenHeightList.add(height);}});},child: Column(children: widget.sectionOfChildrenBuilder.call(context, index),),),);}})),]),))],);
}
四.点击选中分类项时，右侧自动滑动至相应位置

首先，这里需要把右侧列表最后一项的高度设置为ViewPort的高度，保证最后能够滑动到最后一项。只需要在右侧列表添加一个空白区域即可。

@override
Widget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [...,Expanded(child: AfterLayout(callback: (renderBox) {setState(() {...if(widget.itemCount > 0) {_extraHeight = max(renderBox.size.height - _childrenHeightList[widget.itemCount - 1], 0);} else {_extraHeight = 0;}});},child: CustomScrollView(physics: const ClampingScrollPhysics(),slivers: [...,SliverToBoxAdapter(child: SizedBox(height: _extraHeight,),)]),))],);
}

根据前面确定好初始的滑动偏移量之后，就能很方便的控制右侧列表的滑动了，我们通过给右侧列表指定ScrollController，同时调用ScrollController的animateTo(double offset, {required Duration duration, required Curve curve})方法即可。

class _AnchorCategoryListState extends State<AnchorCategoryList> {...final ScrollController _scrollController = ScrollController();int _selectedIndex = 0;bool _scrollLocked = false;@overridevoid initState() {super.initState();if(widget.controller != null) {widget.controller!.addListener(_onIndexChange);}}void _onIndexChange() {if(_selectedIndex == widget.controller!.selectedIndex) {return;}_scrollLocked = true;_selectedIndex = widget.controller!.selectedIndex;widget.controller!.selectTo(_selectedIndex);_scrollController.animateTo(_scrollOffsetList[widget.controller!.selectedIndex],duration: const Duration(milliseconds: 300),curve: Curves.linear).then((value) {_scrollLocked = false;});}@overridevoid dispose() {_scrollController.dispose();if(widget.controller != null) {widget.controller!.removeListener(_onIndexChange);}super.dispose();}@overrideWidget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [...,Expanded(child: AfterLayout(callback: (renderBox) {setState(() {for(int i = 0; i < widget.itemCount; i ++) {double scrollOffset = 0;for(int j=0; j<i; j++) {scrollOffset += _sectionHeightList[j] + _childrenHeightList[j];}if(_scrollOffsetList.length > i) {_scrollOffsetList[i] = scrollOffset;} else {_scrollOffsetList.add(scrollOffset);}}if(widget.itemCount > 0) {_extraHeight = max(renderBox.size.height - _childrenHeightList[widget.itemCount - 1], 0);} else {_extraHeight = 0;}});},child: CustomScrollView(physics: const ClampingScrollPhysics(),controller: _scrollController,slivers: [...]),))],);}}

在这里插入图片描述

五.右侧列表滚动时，动态改变左侧边栏的选中状态

监听右侧列表的滑动，获取滑动位置，与所有子项的初始滑动偏移量对比，可以计算出左侧边栏的哪一个子项应该被选中，然后通过AnchorCategoryController的selectTo(int value)方法更新选中状态即可。

class _AnchorCategoryListState extends State<AnchorCategoryList> {...@overridevoid initState() {super.initState();if(widget.controller != null) {widget.controller!.addListener(_onIndexChange);}_scrollController.addListener(_onScrollChange);}...void _onScrollChange() {if(_scrollLocked) {return;}double scrollOffset = _scrollController.offset;int selectedIndex = 0;for(int index = _scrollOffsetList.length - 1; index >= 0; index --) {selectedIndex = index;if(scrollOffset.roundToDouble() >= _scrollOffsetList[index]) {break;}}if(_selectedIndex != selectedIndex) {_selectedIndex = selectedIndex;widget.controller!.selectTo(selectedIndex);}}@overridevoid dispose() {_scrollController.removeListener(_onScrollChange);_scrollController.dispose();if(widget.controller != null) {widget.controller!.removeListener(_onIndexChange);}super.dispose();}...}
六.控制标题项吸顶

将标题项的SliverToBoxAdapter替换成StickySliverToBoxAdapter即可，关于StickySliverToBoxAdapter可以查看这篇文章02_Flutter自定义Sliver组件实现分组列表吸顶效果。

class _AnchorCategoryListState extends State<AnchorCategoryList> {...@overrideWidget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [...,Expanded(child: AfterLayout(callback: (renderBox) {...},child: CustomScrollView(physics: const ClampingScrollPhysics(),controller: _scrollController,slivers: [...(List<Widget>.generate(widget.itemCount * 2, (allIndex) {int index = allIndex ~/ 2;if(allIndex.isEven) {//sectionWidget sectionItem = AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_sectionHeightList.length > index) {_sectionHeightList[index] = height;} else {_sectionHeightList.add(height);}});},child: widget.sectionItemBuilder.call(context, index),);if(widget.sticky) {return StickySliverToBoxAdapter(child: sectionItem,);} else {return SliverToBoxAdapter(child: sectionItem,);}} else {//children...}})),...]),))],);}}

在这里插入图片描述

搞定，模拟器录屏掉帧了，改用真机录屏😄。

七.完整代码
typedef IndexedWidgetListBuilder = List<Widget> Function(BuildContext context, int index);class AnchorCategoryController extends ChangeNotifier {int selectedIndex = 0;void selectTo(int value) {selectedIndex = value;notifyListeners();}@overridevoid dispose() {selectedIndex = 0;super.dispose();}
}class AnchorCategoryList extends StatefulWidget {final double categoryWidth;final int itemCount;final IndexedWidgetBuilder categoryItemBuilder;final IndexedWidgetBuilder sectionItemBuilder;final IndexedWidgetListBuilder sectionOfChildrenBuilder;final bool sticky;final AnchorCategoryController? controller;const AnchorCategoryList({super.key,required this.categoryItemBuilder,required this.sectionItemBuilder,required this.sectionOfChildrenBuilder,this.controller,double? categoryWidth,int? itemCount,bool? sticky}): categoryWidth = categoryWidth ?? 112,itemCount = itemCount ?? 0,sticky = sticky ?? true;@overrideState<StatefulWidget> createState() => _AnchorCategoryListState();}class _AnchorCategoryListState extends State<AnchorCategoryList> {final List<double> _sectionHeightList = [];final List<double> _childrenHeightList = [];final List<double> _scrollOffsetList = [];double _extraHeight = 0;final ScrollController _scrollController = ScrollController();int _selectedIndex = 0;bool _scrollLocked = false;@overridevoid initState() {super.initState();if(widget.controller != null) {widget.controller!.addListener(_onIndexChange);}_scrollController.addListener(_onScrollChange);}void _onIndexChange() {if(_selectedIndex == widget.controller!.selectedIndex) {return;}_scrollLocked = true;_selectedIndex = widget.controller!.selectedIndex;widget.controller!.selectTo(_selectedIndex);_scrollController.animateTo(_scrollOffsetList[widget.controller!.selectedIndex],duration: const Duration(milliseconds: 300),curve: Curves.linear).then((value) {_scrollLocked = false;});}void _onScrollChange() {if(_scrollLocked) {return;}double scrollOffset = _scrollController.offset;int selectedIndex = 0;for(int index = _scrollOffsetList.length - 1; index >= 0; index --) {selectedIndex = index;if(scrollOffset.roundToDouble() >= _scrollOffsetList[index]) {break;}}if(_selectedIndex != selectedIndex) {_selectedIndex = selectedIndex;widget.controller!.selectTo(selectedIndex);}}@overridevoid dispose() {_scrollController.removeListener(_onScrollChange);_scrollController.dispose();if(widget.controller != null) {widget.controller!.removeListener(_onIndexChange);}super.dispose();}@overrideWidget build(BuildContext context) {return Row(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: [SizedBox(width: widget.categoryWidth,child: LayoutBuilder(builder: (context, viewportConstraints) {return SingleChildScrollView(child: ConstrainedBox(constraints: BoxConstraints(minHeight: viewportConstraints.maxHeight != double.infinity ? viewportConstraints.maxHeight:0),child: Column(mainAxisSize: MainAxisSize.max,mainAxisAlignment: MainAxisAlignment.start,crossAxisAlignment: CrossAxisAlignment.stretch,children: List.generate(widget.itemCount, (index) {return widget.categoryItemBuilder.call(context, index);}),),),);},)),Expanded(child: AfterLayout(callback: (renderBox) {setState(() {for(int i = 0; i < widget.itemCount; i ++) {double scrollOffset = 0;for(int j=0; j<i; j++) {scrollOffset += _sectionHeightList[j] + _childrenHeightList[j];}if(_scrollOffsetList.length > i) {_scrollOffsetList[i] = scrollOffset;} else {_scrollOffsetList.add(scrollOffset);}}if(widget.itemCount > 0) {_extraHeight = max(renderBox.size.height - _childrenHeightList[widget.itemCount - 1], 0);} else {_extraHeight = 0;}});},child: CustomScrollView(physics: const ClampingScrollPhysics(),controller: _scrollController,slivers: [...(List<Widget>.generate(widget.itemCount * 2, (allIndex) {int index = allIndex ~/ 2;if(allIndex.isEven) {//sectionWidget sectionItem = AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_sectionHeightList.length > index) {_sectionHeightList[index] = height;} else {_sectionHeightList.add(height);}});},child: widget.sectionItemBuilder.call(context, index),);if(widget.sticky) {return StickySliverToBoxAdapter(child: sectionItem,);} else {return SliverToBoxAdapter(child: sectionItem,);}} else {//childrenreturn SliverToBoxAdapter(child: AfterLayout(callback: (renderBox) {double height = renderBox.size.height;setState(() {if(_childrenHeightList.length > index) {_childrenHeightList[index] = height;} else {_childrenHeightList.add(height);}});},child: Column(children: widget.sectionOfChildrenBuilder.call(context, index),),),);}})),SliverToBoxAdapter(child: SizedBox(height: _extraHeight,),)]),))],);}}

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多态分为两种：通用的多态和特定的多态。两者的区别是前者对工作的类型不加限制，允许对不同类型的值执行相同的代码；后者只对有限数量的类型有效，而且对不同类型的值可能要执行不同的代码。 1，通用的多态又分为参数多态（parametric）和包含多态（inclusion）； (1)参数多态：采用参数化模板，通过给出不同的类型参数，使得一个结构有多种类型。 例如：泛型   (2)包含多
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