How to make sticky headers work with a NestedScrollView in Flutter? - flutter

Question

I have a requirement to build a view that has a tab bar within a collapsible app bar (so when the app bar collapses, just the tabs are visible) which controls a tab view, each of which will host a different sub view. Further, within those subviews on each tab, the content should be scrollable (which impacts the collapsed state of the app bar), and widgets within that scrollable view need to have headers that "stick" to the bottom of the app bar/tab bar.
A sliver-based implementation of sticky headers are available here: Flutter Sticky Headers
I took the first sample from Flutter's documentation on this page:
https://api.flutter.dev/flutter/widgets/NestedScrollView-class.html#widgets.NestedScrollView.1
and wrapped the SliverFixedExtentList in a SliverStickyHeader element and the headers are not sticking to the top of the list. I've tried this in a variety of places but can't seem to make a sticky header work using this library or even the original which used RenderObjects. Any thoughts as to why this might be?
Here's the full code as an example:
import 'package:flutter/material.dart';
import 'package:flutter_sticky_header/flutter_sticky_header.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
static const String _title = 'Flutter Code Sample';
#override
Widget build(BuildContext context) {
return const MaterialApp(
title: _title,
home: MyStatelessWidget(),
);
}
}
class MyStatelessWidget extends StatelessWidget {
const MyStatelessWidget({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
final List<String> _tabs = <String>['Tab 1', 'Tab 2'];
return DefaultTabController(
length: _tabs.length, // This is the number of tabs.
child: Scaffold(
body: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
// These are the slivers that show up in the "outer" scroll view.
return <Widget>[
SliverOverlapAbsorber(
// This widget takes the overlapping behavior of the SliverAppBar,
// and redirects it to the SliverOverlapInjector below. If it is
// missing, then it is possible for the nested "inner" scroll view
// below to end up under the SliverAppBar even when the inner
// scroll view thinks it has not been scrolled.
// This is not necessary if the "headerSliverBuilder" only builds
// widgets that do not overlap the next sliver.
handle:
NestedScrollView.sliverOverlapAbsorberHandleFor(context),
sliver: SliverAppBar(
title:
const Text('Books'), // This is the title in the app bar.
pinned: true,
expandedHeight: 150.0,
// The "forceElevated" property causes the SliverAppBar to show
// a shadow. The "innerBoxIsScrolled" parameter is true when the
// inner scroll view is scrolled beyond its "zero" point, i.e.
// when it appears to be scrolled below the SliverAppBar.
// Without this, there are cases where the shadow would appear
// or not appear inappropriately, because the SliverAppBar is
// not actually aware of the precise position of the inner
// scroll views.
forceElevated: innerBoxIsScrolled,
bottom: TabBar(
// These are the widgets to put in each tab in the tab bar.
tabs: _tabs.map((String name) => Tab(text: name)).toList(),
),
),
),
];
},
body: TabBarView(
// These are the contents of the tab views, below the tabs.
children: _tabs.map((String name) {
return SafeArea(
top: false,
bottom: false,
child: Builder(
// This Builder is needed to provide a BuildContext that is
// "inside" the NestedScrollView, so that
// sliverOverlapAbsorberHandleFor() can find the
// NestedScrollView.
builder: (BuildContext context) {
return CustomScrollView(
// The "controller" and "primary" members should be left
// unset, so that the NestedScrollView can control this
// inner scroll view.
// If the "controller" property is set, then this scroll
// view will not be associated with the NestedScrollView.
// The PageStorageKey should be unique to this ScrollView;
// it allows the list to remember its scroll position when
// the tab view is not on the screen.
key: PageStorageKey<String>(name),
slivers: <Widget>[
SliverOverlapInjector(
// This is the flip side of the SliverOverlapAbsorber
// above.
handle:
NestedScrollView.sliverOverlapAbsorberHandleFor(
context),
),
SliverPadding(
padding: const EdgeInsets.all(8.0),
// In this example, the inner scroll view has
// fixed-height list items, hence the use of
// SliverFixedExtentList. However, one could use any
// sliver widget here, e.g. SliverList or SliverGrid.
sliver: SliverStickyHeader(
header: Text('header'),
sliver: SliverFixedExtentList(
// The items in this example are fixed to 48 pixels
// high. This matches the Material Design spec for
// ListTile widgets.
itemExtent: 48.0,
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
// This builder is called for each child.
// In this example, we just number each list item.
return ListTile(
title: Text('Item $index'),
);
},
// The childCount of the SliverChildBuilderDelegate
// specifies how many children this inner list
// has. In this example, each tab has a list of
// exactly 30 items, but this is arbitrary.
childCount: 30,
),
),
),
),
],
);
},
),
);
}).toList(),
),
),
),
);
}
}

Answer 1

I think the problem has something to do with the SliverOverlapInjector there is a workaround mentioned in this issue comment: https://github.com/flutter/flutter/issues/91972#issuecomment-995462622
Basically you need an improved overlap injector ( SliverPinnedOverlapInjector):
DISCLAIMER: The following source code is directly copied from the issue comment:
import 'dart:math';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
class SliverPinnedOverlapInjector extends SingleChildRenderObjectWidget {
const SliverPinnedOverlapInjector({
required this.handle,
Key? key,
}) : super(key: key);
final SliverOverlapAbsorberHandle handle;
#override
RenderSliverPinnedOverlapInjector createRenderObject(BuildContext context) {
return RenderSliverPinnedOverlapInjector(
handle: handle,
);
}
#override
void updateRenderObject(
BuildContext context,
RenderSliverPinnedOverlapInjector renderObject,
) {
renderObject.handle = handle;
}
}
class RenderSliverPinnedOverlapInjector extends RenderSliver {
RenderSliverPinnedOverlapInjector({
required SliverOverlapAbsorberHandle handle,
}) : _handle = handle;
double? _currentLayoutExtent;
double? _currentMaxExtent;
SliverOverlapAbsorberHandle get handle => _handle;
SliverOverlapAbsorberHandle _handle;
set handle(SliverOverlapAbsorberHandle value) {
if (handle == value) return;
if (attached) {
handle.removeListener(markNeedsLayout);
}
_handle = value;
if (attached) {
handle.addListener(markNeedsLayout);
if (handle.layoutExtent != _currentLayoutExtent ||
handle.scrollExtent != _currentMaxExtent) markNeedsLayout();
}
}
#override
void attach(PipelineOwner owner) {
super.attach(owner);
handle.addListener(markNeedsLayout);
if (handle.layoutExtent != _currentLayoutExtent ||
handle.scrollExtent != _currentMaxExtent) markNeedsLayout();
}
#override
void detach() {
handle.removeListener(markNeedsLayout);
super.detach();
}
#override
void performLayout() {
_currentLayoutExtent = handle.layoutExtent;
final paintedExtent = min(
_currentLayoutExtent!,
constraints.remainingPaintExtent - constraints.overlap,
);
geometry = SliverGeometry(
paintExtent: paintedExtent,
maxPaintExtent: _currentLayoutExtent!,
maxScrollObstructionExtent: _currentLayoutExtent!,
paintOrigin: constraints.overlap,
scrollExtent: _currentLayoutExtent!,
layoutExtent: max(0, paintedExtent - constraints.scrollOffset),
hasVisualOverflow: paintedExtent < _currentLayoutExtent!,
);
}
}
Just copy the SliverPinnedOverlapInjector to your project and use it as a drop-in replacement for the SliverOverlapInjector. In my case this was the only change necessary. Everything else should stay the same.

Answer 2

Scaffold(
body: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return <Widget>[
SliverAppBar(
centerTitle: false,
automaticallyImplyLeading: false,
backgroundColor: Colors.black,
title: Text('Murder series (Event That Happen)'),
actions: <Widget>[
],
child: Container(
height: 20,
width: 20,
child: SvgPicture.asset(
'assets/library_pre.svg',
color: Colors.white,
),
),
),
),
],
expandedHeight: 200.0,
floating: true,
pinned: true,
flexibleSpace: FlexibleSpaceBar(
background: Container(
child: Column(
children: [
SizedBox(
height: 70,
),
Expanded(
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
CircleAvatar(
radius: 40,
backgroundImage:
AssetImage('assets/forumPage.png'),
),
Text(
'74 Members',
style: TextStyle(
fontSize: 25,
color: Colors.white,
),
),
overlapped(),
Text(
'Leave',
style: TextStyle(
fontSize: 25,
color: Colors.red,
),
)
],
),
),
),
Container(
height: 30,
width: double.infinity,
decoration: BoxDecoration(color: Colors.red),
)
],
),
)),
),
];
},
body: SingleChildScrollView(
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 15.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
],
),
],
),
))),
);