成都网站建设排行榜,外贸生意做哪个网站好,网站seo教程,湖南平台网站建设方案02_Flutter自定义Sliver组件实现分组列表吸顶效果 一.先上效果图 二.列表布局实现
比较简单#xff0c;直接上代码#xff0c;主要使用CustomScrollView和SliverToBoxAdapter实现
_buildSection(String title) {return SliverToBoxAdapter(child: RepaintBoundary(child: C… 02_Flutter自定义Sliver组件实现分组列表吸顶效果
一.先上效果图 二.列表布局实现
比较简单直接上代码主要使用CustomScrollView和SliverToBoxAdapter实现
_buildSection(String title) {return SliverToBoxAdapter(child: RepaintBoundary(child: Container(height: 50,color: Colors.brown,alignment: Alignment.center,child: Text(title),),));
}_buildItem(String title) {return SliverToBoxAdapter(child: RepaintBoundary(child: Container(padding: const EdgeInsets.symmetric(horizontal: 15),height: 70,color: Colors.cyanAccent,alignment: Alignment.centerLeft,child: Text(title),),));
}CustomScrollView(slivers: [_buildSection(蜀汉五虎将),_buildItem(关羽),_buildItem(张飞),_buildItem(赵云),_buildItem(马超),_buildItem(黄忠),_buildSection(虎贲双雄),_buildItem(许褚),_buildItem(典韦),_buildSection(五子良将),_buildItem(张辽),_buildItem(乐进),_buildItem(于禁),_buildItem(张郃),_buildItem(徐晃),_buildSection(八虎骑),_buildItem(夏侯惇),_buildItem(夏侯渊),_buildItem(曹仁),_buildItem(曹纯),_buildItem(曹洪),_buildItem(曹休),_buildItem(夏侯尚),_buildItem(曹真)],
)三.SliverToBoxAdapter和SliverPersistentHeader
可以使用Flutter提供的SliverPersistentHeader组件实现在使用SliverPersistentHeader时要求我们明确指定子控件的高度不支持吸顶上推效果使用起来不够灵活所以我们参考并结合SliverToBoxAdapter和SliverPersistentHeader源码自己实现一个自适应高度的吸顶Sliver组件并在此基础上一步步实现吸顶上推效果。
编写StickySliverToBoxAdapter类继承自SingleChildRenderObjectWidget
class StickySliverToBoxAdapter extends SingleChildRenderObjectWidget {const StickySliverToBoxAdapter({super.key,super.child});overrideRenderObject createRenderObject(BuildContext context) _StickyRenderSliverToBoxAdapter();}SingleChildRenderObjectWidget类要求我们自己实现createRenderObject方法返回一个RenderObject对象而对于一个S liver组件而言这个RenderObject必须是RenderSilver的子类。
编写_StickyRenderSliverToBoxAdapter继承RenderSliverSingleBoxAdapter
class _StickyRenderSliverToBoxAdapter extends RenderSliverSingleBoxAdapter {overridevoid performLayout() {// TODO: implement performLayout}}RenderSliverSingleBoxAdapter要求子类实现performLayout方法performLayout会对widegt的布局和绘制做控制实现吸顶效果的关键就在于performLayout方法的实现。先依次看下SliverToBoxAdapter和SliverPersistentHeader对应RenderObject的performLayout相关方法的实现。
RenderSliverToBoxAdapter#performLayout
override
void performLayout() {if (child null) {geometry SliverGeometry.zero;return;}final SliverConstraints constraints this.constraints;//摆放子View并把constraints传递给子Viewchild!.layout(constraints.asBoxConstraints(), parentUsesSize: true);//获取子View在滑动主轴方向的尺寸final double childExtent;switch (constraints.axis) {case Axis.horizontal:childExtent child!.size.width;case Axis.vertical:childExtent child!.size.height;}final double paintedChildSize calculatePaintOffset(constraints, from: 0.0, to: childExtent);final double cacheExtent calculateCacheOffset(constraints, from: 0.0, to: childExtent);assert(paintedChildSize.isFinite);assert(paintedChildSize 0.0);//更新SliverGeometrygeometry SliverGeometry(scrollExtent: childExtent,paintExtent: paintedChildSize,cacheExtent: cacheExtent,maxPaintExtent: childExtent,hitTestExtent: paintedChildSize,hasVisualOverflow: childExtent constraints.remainingPaintExtent || constraints.scrollOffset 0.0,);//更新paintOffset由滑动偏移量constraints.scrollOffset决定setChildParentData(child!, constraints, geometry!);
}RenderSliverFloatingPersistentHeader#performLayout
SliverPersistentHeader的performLayout方法中调用了updateGeometry方法去更新geometry而吸顶的关键就在updateGeometry方法中也就是paintOrigin的值。constraints.overlap的值代表前一个Sliver和当前Sliver被覆盖部分的高度。
override
double updateGeometry() {final double minExtent this.minExtent;final double minAllowedExtent constraints.remainingPaintExtent minExtent ?minExtent :constraints.remainingPaintExtent;final double maxExtent this.maxExtent;final double paintExtent maxExtent - _effectiveScrollOffset!;final double clampedPaintExtent clampDouble(paintExtent,minAllowedExtent,constraints.remainingPaintExtent,);final double layoutExtent maxExtent - constraints.scrollOffset;final double stretchOffset stretchConfiguration ! null ?constraints.overlap.abs() :0.0;geometry SliverGeometry(scrollExtent: maxExtent,paintOrigin: math.min(constraints.overlap, 0.0),paintExtent: clampedPaintExtent,layoutExtent: clampDouble(layoutExtent, 0.0, clampedPaintExtent),maxPaintExtent: maxExtent stretchOffset,maxScrollObstructionExtent: minExtent,hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.);return 0.0;
}四.吸顶效果实现
直接把上面updateGeometry中设置SliverGeometry的代码拷贝到_StickyRenderSliverToBoxAdapter#performLayout实现中maxExtent和minExtent这两个值是由SliverPersistentHeader传入的SliverPersistentHeaderDelegate对象提供的。这里可以自己去看SliverPersistentHeaderDelegate的源码就不多废话了。我们只需要把maxExtent和minExtent这两个值都改为子控件在主轴方向的尺寸大小即可。 _buildSection(String title) {return StickySliverToBoxAdapter(child: RepaintBoundary(child: Container(height: 50,color: Colors.brown,alignment: Alignment.center,child: Text(title),),));}class _StickyRenderSliverToBoxAdapter extends RenderSliverSingleBoxAdapter {overridevoid performLayout() {if (child null) {geometry SliverGeometry.zero;return;}final SliverConstraints constraints this.constraints;//摆放子View并把constraints传递给子Viewchild!.layout(constraints.asBoxConstraints(), parentUsesSize: true);//获取子View在滑动主轴方向的尺寸final double childExtent;switch (constraints.axis) {case Axis.horizontal:childExtent child!.size.width;case Axis.vertical:childExtent child!.size.height;}final double minExtent childExtent;final double minAllowedExtent constraints.remainingPaintExtent minExtent ?minExtent : constraints.remainingPaintExtent;final double maxExtent childExtent;final double paintExtent maxExtent;final double clampedPaintExtent clampDouble(paintExtent,minAllowedExtent,constraints.remainingPaintExtent,);final double layoutExtent maxExtent - constraints.scrollOffset;geometry SliverGeometry(scrollExtent: maxExtent,paintOrigin: min(constraints.overlap, 0.0),paintExtent: clampedPaintExtent,layoutExtent: clampDouble(layoutExtent, 0.0, clampedPaintExtent),maxPaintExtent: maxExtent,maxScrollObstructionExtent: minExtent,hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.);}
}仔细看上面的效果貌似只有第一个Sliver吸顶了我们把分组item的背景改成透明的再来看看效果就知道怎么回事了。 可以看到所有的分组section都已经吸顶了只不过吸顶位置都是0并且前一个section把后一个section覆盖了我们下一步实现上推功能后这个问题自热而然的就解决了。
五.实现上推效果 如图当前section与前一个section重合了多少前一个section就往上移动多少也就是移动constraints.overlap即可往下滑动也是同样的道理。
//查找前一个吸顶的section
RenderSliver? _prev() {if(parent is RenderViewportBase) {RenderSliver? current this;while(current ! null) {current (parent as RenderViewportBase).childBefore(current);if(current is _StickyRenderSliverToBoxAdapter current.geometry ! null) {return current;}}}return null;
}override
void performLayout() {if (child null) {geometry SliverGeometry.zero;return;}final SliverConstraints constraints this.constraints;//摆放子View并把constraints传递给子Viewchild!.layout(constraints.asBoxConstraints(), parentUsesSize: true);//获取子View在滑动主轴方向的尺寸final double childExtent;switch (constraints.axis) {case Axis.horizontal:childExtent child!.size.width;case Axis.vertical:childExtent child!.size.height;}final double minExtent childExtent;final double minAllowedExtent constraints.remainingPaintExtent minExtent ?minExtent : constraints.remainingPaintExtent;final double maxExtent childExtent;final double paintExtent maxExtent;final double clampedPaintExtent clampDouble(paintExtent,minAllowedExtent,constraints.remainingPaintExtent,);final double layoutExtent maxExtent - constraints.scrollOffset;geometry SliverGeometry(scrollExtent: maxExtent,paintOrigin: min(constraints.overlap, 0.0),paintExtent: clampedPaintExtent,layoutExtent: clampDouble(layoutExtent, 0.0, clampedPaintExtent),maxPaintExtent: maxExtent,maxScrollObstructionExtent: minExtent,hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.);//上推关键代码: 当前吸顶的Sliver被覆盖了多少前一个吸顶的Sliver就移动多少RenderSliver? prev _prev();if(prev ! null constraints.overlap 0) {setChildParentData(_prev()!, constraints.copyWith(scrollOffset: constraints.overlap), _prev()!.geometry!);}
}搞定可以洗洗睡了嘿嘿。 六.Fixed: 吸顶section点击事件失效
重写childMainAxisPosition方法返回0即可
class _StickyRenderSliverToBoxAdapter extends RenderSliverSingleBoxAdapter {...// 必须重写否则点击事件失效。overridedouble childMainAxisPosition(covariant RenderBox child) 0.0;}
