概述
Flutter Sliver滚动组件
SliverList & SliverGrid
需要同时滚动ListView和GridView时可以使用SliverList和SliverGrid。
CustomScrollView(
slivers: [
SliverList(
delegate: SliverChildBuilderDelegate(
(context, index) {
return Container(
height: 50,
color: Colors.primaries[index % Colors.primaries.length],
);
},
childCount: 5,
),
),
SliverGrid(
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 3,
crossAxisSpacing: 5,
mainAxisSpacing: 5,
),
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
color: Colors.primaries[index % Colors.primaries.length],
);
},
childCount: 20,
),
),
],
)
SliverAppBar
pinned：是否固定在屏幕顶部。
expandedHeight：展开区域的高度。
flexibleSpace：展开取消显示内容。
CustomScrollView(
slivers: [
SliverAppBar(
pinned: true,
expandedHeight: 200,
flexibleSpace: FlexibleSpaceBar(
title: const Text("SliverAppBar"),
background: Image.asset("images/avatar.jpg", fit: BoxFit.cover),
),
),
SliverFixedExtentList(
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
alignment: Alignment.center,
color: Colors.primaries[index % Colors.primaries.length],
child: Text("$index"),
);
},
),
itemExtent: 50.0,
),
],
)
SliverPersistentHeader
SliverPersistentHeader组件可以控制滚动的最大高度和最小高度，类似SliverAppBar效果。
build：显示内容。
maxExtent & minExtent：滚动的高度范围。
shouldRebuild：是否需要更新。
CustomScrollView(
slivers: [
SliverPersistentHeader(
pinned: true,
delegate: MySliverPersistentHeaderDelegate(),
),
SliverGrid(
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 3,
crossAxisSpacing: 5,
mainAxisSpacing: 5,
),
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
color: Colors.primaries[index % Colors.primaries.length],
);
},
),
),
],
)
class MySliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
@override
Widget build(
BuildContext context, double shrinkOffset, bool overlapsContent) {
return Container(
color: Colors.blue,
alignment: Alignment.center,
child: Text(
"hello world",
style: TextStyle(color: Colors.white),
),
);
}
@override
double get maxExtent => 200;
@override
double get minExtent => 50;
@override
bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
return false;
}
}
SliverToBoxAdapter
CustomScrollView只能包含Sliver组件，如果需要使用普通组件可以使用SliverToBoxAdapter。
CustomScrollView(
slivers: [
SliverToBoxAdapter(
child: Container(
height: 200,
color: Colors.black26,
alignment: Alignment.center,
child: Text("hello world"),
),
),
SliverList(
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
height: 60,
color: Colors.primaries[index % Colors.primaries.length],
);
},
childCount: 50,
),
),
],
)
CustomScrollView & NestedScrollView
CustomScrollView组件可以将多个组件组合在一起，具有统一的滚动效果，但是CustomScrollView只能嵌套Sliver系列的组件，如SliverList、SliverGrid、SliverPadding、SliverAppBar等。
NestedScrollView可以协调两个滚动组件滑动。NestedScrollView在逻辑上将可滚动组件分为header和body两部分，heade部分只能接收Sliver类型的组件，而body部分可以接收任意类型的组件。
NestedScrollView+SliverAppBar+SliverFixedExtentList+ListView
NestedScrollView(
//Sliver组件
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
SliverAppBar(
title: const Text("嵌套ListView"),
pinned: true, //固定AppBar
forceElevated: true,
),
SliverFixedExtentList(
itemExtent: 50,
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return ListTile(title: Text("$index"));
},
childCount: 5,
),
),
];
},
//滚动组件
body: ListView.builder(
padding: const EdgeInsets.all(8),
physics: const ClampingScrollPhysics(), //需要
itemCount: 30,
itemBuilder: (BuildContext context, int index) {
return SizedBox(
height: 50,
child: Center(child: Text("item $index")),
);
},
),
)
NestedScrollView+SliverAppBar+CustomScrollView
NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
SliverAppBar(
floating: true,
snap: true,
expandedHeight: 200,
forceElevated: innerBoxIsScrolled,
flexibleSpace: FlexibleSpaceBar(
background: Image.asset(
"images/logo.png",
fit: BoxFit.cover,
),
),
),
];
},
body: CustomScrollView(
slivers: [buildSliverList(50)],
),
)
优化联动效果
SliverAppBar+CustomScrollView组合，当反向滑动时，SliverAppBar就会整体回到屏幕顶部，出现遮挡问题，为了解决该问题，可以用在header里用SliverOverlapAbsorber组件包裹SliverAppBar，body里Sliver列表最前面添加一个SliverOverlapInjector。
NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
SliverOverlapAbsorber(
handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
sliver: SliverAppBar(
floating: true,
snap: true,
expandedHeight: 200,
forceElevated: innerBoxIsScrolled,
flexibleSpace: FlexibleSpaceBar(
background: Image.asset(
"images/logo.png",
fit: BoxFit.cover,
),
),
),
),
];
},
body: Builder(
builder: (BuildContext context) {
return CustomScrollView(
slivers: [
SliverOverlapInjector(
handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
),
buildSliverList(50),
],
);
},
),
)
NestedScrollView+TabBarView
class MyPageView extends StatefulWidget {
late List<String> tabs;
MyPageView({Key? key, required this.tabs}) : super(key: key);
@override
State<StatefulWidget> createState() {
return _MyPageViewState();
}
}
class _MyPageViewState extends State<MyPageView>
with SingleTickerProviderStateMixin {
late TabController _controller;
@override
void initState() {
super.initState();
_controller = TabController(length: widget.tabs.length, vsync: this);
}
@override
void dispose() {
super.dispose();
_controller.dispose();
}
@override
Widget build(BuildContext context) {
return NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
SliverOverlapAbsorber(
handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
sliver: SliverAppBar(
title: const Text("hi Flutter"),
floating: true,
snap: true,
forceElevated: innerBoxIsScrolled,
bottom: TabBar(
controller: _controller,
tabs: widget.tabs.map((e) => Tab(text: e)).toList(),
),
),
),
];
},
body: TabBarView(
controller: _controller,
children: widget.tabs.map((e) {
return Builder(builder: (BuildContext context) {
return CustomScrollView(
key: PageStorageKey(e),
slivers: [
SliverOverlapInjector(
handle:
NestedScrollView.sliverOverlapAbsorberHandleFor(context),
),
SliverPadding(
padding: const EdgeInsets.all(9),
sliver: buildSliverList(50),
),
],
);
});
}).toList(),
),
);
}
}
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