SliverPersistentHeaderDelegate not fully collapsed - flutter

Question

I'm having a hard time making a custom collapsing toolbar, attached below is a video for a normal case.
Then here's a screen record of the misbehavior, most of the time this happens.
Aside from the fact that the scrolling is not so snappy, you'll see in the second video that the sliver on the top is not completely collapsed.
Do you have any suggestion to improve the performance of the app and a solution for the bug?
here's my code inside the SliverPersistentHeaderDelegate
class DashboardHeaderPersistentDelegate extends SliverPersistentHeaderDelegate {
...
#override
Widget build(
BuildContext context, double shrinkOffset, bool overlapsContent) {
double shrinkPercentage = min(1, shrinkOffset / (maxExtent - minExtent));
double titleTopMargin = titleCollapsedTopPadding +
(titleExpandedTopPadding - titleCollapsedTopPadding) *
(1 - shrinkPercentage);
double titleFontSize = titleCollapsedFontSize +
(titleExpandedFontSize - titleCollapsedFontSize) *
(1 - shrinkPercentage);
double infoWidgetHeight = minExtent +
(maxExtent - minExtent) -
shrinkOffset -
titleTopMargin -
titleFontSize -
44;
double collapasedInfoOpacity = max(0, shrinkPercentage-.7)/.3;
return Material(
elevation: 0,
shadowColor: Colors.white,
child: SafeArea(
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
height: titleFontSize,
alignment: Alignment.center,
child: Text(
'\$ 5329.05',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: titleFontSize,
fontWeight: FontWeight.w500),
),
margin: EdgeInsets.only(top: titleTopMargin, bottom: 8),
),
Container(
height: shrinkPercentage == 1 ? 20 : infoWidgetHeight,
width: MediaQuery.of(context).size.width,
alignment: Alignment.center,
child: Stack(
alignment: Alignment.bottomCenter,
children: [
Opacity(
opacity: 1 - shrinkPercentage,
child: _buildInformationWidget(context),
),
Opacity(
opacity: collapasedInfoOpacity,
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 8),
child: _buildCollapsedInformationWidget(),
),
)
],
),
)
],
),
),
);
}
Widget _buildInformationWidget(BuildContext context) => ClipRect(
child: OverflowBox(
maxWidth: double.infinity,
maxHeight: double.infinity,
child: FittedBox(
fit: BoxFit.fitWidth,
alignment: Alignment.center,
child: Container(
width: MediaQuery.of(context).size.width,
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Text(
'AVAILABLE BALANCE',
style: TextStyle(
fontSize: 12,
fontWeight: FontWeight.w900,
color: Colors.black26),
),
Padding(
padding: const EdgeInsets.only(top: 16),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: 100,
child: Text(
'\$ 11200',
textAlign: TextAlign.right,
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 18,
fontWeight: FontWeight.w700,
color: Colors.green[400]),
),
),
Text(
' I ',
style: TextStyle(fontSize: 20, color: Colors.black12),
),
Container(
width: 100,
child: Text(
'\$ 400',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 18,
fontWeight: FontWeight.w700,
color: Colors.red[400]),
),
)
],
),
),
Container(
margin: EdgeInsets.only(left: 12, top: 12),
alignment: Alignment.centerLeft,
child: Text(
"CATEGORIES",
style: TextStyle(
fontSize: 12,
fontWeight: FontWeight.w900,
color: Colors.black26),
),
),
Container(
height: 88,
child: ListView.builder(
scrollDirection: Axis.horizontal,
itemCount: categories.length,
itemBuilder: (context, index) {
return Padding(
padding: EdgeInsets.only(
left: (index == 0) ? 24.0 : 8.0,
right: (index == categories.length - 1)
? 24.0
: 8.0),
child: _buildCategoryItem(
categoriesIcons[index], categories[index], .9),
);
}),
)
],
),
),
),
),
);
Widget _buildCollapsedInformationWidget() => Row(
children: [
Text("Recent"),
Spacer(),
Container(
child: Text(
'\$ 11200',
textAlign: TextAlign.right,
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 14,
fontWeight: FontWeight.w700,
color: Colors.green[400]),
),
),
Text(
' I ',
style: TextStyle(fontSize: 20, color: Colors.black12),
),
Container(
child: Text(
'\$ 400',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 14,
fontWeight: FontWeight.w700,
color: Colors.red[400]),
),
)
],
);
Widget _buildCategoryItem(
IconData data, String categoryTitle, double percentage) =>
Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Stack(
alignment: Alignment.center,
children: <Widget>[
Container(
decoration: BoxDecoration(
border: Border.all(width: 1, color: Colors.black12),
borderRadius: BorderRadius.circular(28),
color: Colors.blue[400]),
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Icon(
data,
size: 28,
color: Colors.white,
),
),
),
Container(
width: 40,
height: 40,
child: CircularProgressIndicator(
value: percentage,
strokeWidth: 2,
valueColor: AlwaysStoppedAnimation(Colors.white),
),
)
],
),
Container(
width: 72,
alignment: Alignment.center,
child: Text(categoryTitle,
overflow: TextOverflow.ellipsis,
textAlign: TextAlign.center,
maxLines: 1,
style: TextStyle(
fontSize: 14,
fontWeight: FontWeight.w400,
color: Colors.black45)),
)
],
);
...
}

Answer 1

When it's possible..Use dependend on parent size widgets insted of calcualting children sizes manualy.
FittedBox. Can scale the font size of the children widget according on parents size and fit parameter.
ConstrainedBox, BoxConstraints.tightFor
Expanded. Probably you know how it works.
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
body: SafeArea(
child: MyHomePage(),
),
),
);
}
}
class MyHomePage extends StatefulWidget {
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return CustomScrollView(
slivers: [
SliverPersistentHeader(
pinned: true,
floating: false,
delegate: DashboardHeaderPersistentDelegate(),
),
SliverList(
delegate: SliverChildBuilderDelegate(
(_, i) => Card(
margin: const EdgeInsets.all(10),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: [
Expanded(
flex: 1,
child: Text(
i.toString(),
),
),
const Expanded(
flex: 3,
child: Text('Text'),
),
],
),
),
),
childCount: 100,
),
),
],
);
}
}
const categories = [
'Grocieries',
'Transport',
'House Rent',
'Shopping',
'Career'
];
const categoriesIcons = [
Icons.ac_unit,
Icons.access_alarms,
Icons.dashboard,
Icons.accessible_forward,
Icons.backspace,
];
class DashboardHeaderPersistentDelegate extends SliverPersistentHeaderDelegate {
#override
Widget build(
BuildContext context, double shrinkOffset, bool overlapsContent) {
double shrinkPercentage = min(1, shrinkOffset / (maxExtent - minExtent));
return Container(
decoration: BoxDecoration(
border: Border.all(
color: Colors.blueAccent,
),
),
child: Material(
elevation: 0,
shadowColor: Colors.white,
child: SafeArea(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
ConstrainedBox(
constraints: BoxConstraints.tightFor(
height: max(
60,
100 * (1 - shrinkPercentage),
),
),
child: FittedBox(
child: Container(
padding: EdgeInsets.all(20),
width: 200,
child: const Text(
'\$ 5329.05',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 30,
fontWeight: FontWeight.w500,
),
),
),
),
),
Expanded(
child: Stack(
alignment: Alignment.bottomCenter,
children: [
if (shrinkPercentage != 1)
Opacity(
opacity: 1 - shrinkPercentage,
child: _buildInformationWidget(context),
),
if (shrinkPercentage != 0)
Opacity(
opacity: shrinkPercentage,
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 8),
child: _buildCollapsedInformationWidget(),
),
),
],
),
)
],
),
),
),
);
}
Widget _buildInformationWidget(BuildContext context) => ClipRect(
child: OverflowBox(
maxWidth: double.infinity,
maxHeight: double.infinity,
child: FittedBox(
fit: BoxFit.fitWidth,
alignment: Alignment.center,
child: Container(
width: MediaQuery.of(context).size.width,
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
const Text(
'AVAILABLE BALANCE',
style: TextStyle(
fontSize: 12,
fontWeight: FontWeight.w900,
color: Colors.black26),
),
Padding(
padding: const EdgeInsets.only(top: 16),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: 100,
child: Text(
'\$ 11200',
textAlign: TextAlign.right,
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 18,
fontWeight: FontWeight.w700,
color: Colors.green[400],
),
),
),
const Text(
' I ',
style: TextStyle(
fontSize: 20,
color: Colors.black12,
),
),
Container(
width: 100,
child: Text(
'\$ 400',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 18,
fontWeight: FontWeight.w700,
color: Colors.red[400],
),
),
)
],
),
),
Container(
margin: EdgeInsets.only(left: 12, top: 12),
alignment: Alignment.centerLeft,
child: const Text(
"CATEGORIES",
style: TextStyle(
fontSize: 12,
fontWeight: FontWeight.w900,
color: Colors.black26,
),
),
),
Container(
height: 88,
child: ListView.builder(
scrollDirection: Axis.horizontal,
itemCount: categories.length,
itemBuilder: (context, index) {
return Padding(
padding: EdgeInsets.only(
left: (index == 0) ? 24.0 : 8.0,
right: (index == categories.length - 1)
? 24.0
: 8.0),
child: _buildCategoryItem(
categoriesIcons[index],
categories[index],
.9,
),
);
},
),
)
],
),
),
),
),
);
Widget _buildCollapsedInformationWidget() => Row(
children: [
const Text("Recent"),
const Spacer(),
Container(
child: Text(
'\$ 11200',
textAlign: TextAlign.right,
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 14,
fontWeight: FontWeight.w700,
color: Colors.green[400],
),
),
),
const Text(
' I ',
style: TextStyle(
fontSize: 20,
color: Colors.black12,
),
),
Container(
child: Text(
'\$ 400',
style: TextStyle(
fontFamily: 'Barlow',
fontSize: 14,
fontWeight: FontWeight.w700,
color: Colors.red[400],
),
),
)
],
);
Widget _buildCategoryItem(
IconData data, String categoryTitle, double percentage) =>
Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Stack(
alignment: Alignment.center,
children: <Widget>[
Container(
decoration: BoxDecoration(
border: Border.all(
width: 1,
color: Colors.black12,
),
borderRadius: BorderRadius.circular(28),
color: Colors.blue[400],
),
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Icon(
data,
size: 28,
color: Colors.white,
),
),
),
Container(
width: 40,
height: 40,
child: CircularProgressIndicator(
value: percentage,
strokeWidth: 2,
valueColor: AlwaysStoppedAnimation(Colors.white),
),
)
],
),
Container(
width: 72,
alignment: Alignment.center,
child: Text(
categoryTitle,
overflow: TextOverflow.ellipsis,
textAlign: TextAlign.center,
maxLines: 1,
style: const TextStyle(
fontSize: 14,
fontWeight: FontWeight.w400,
color: Colors.black45,
),
),
)
],
);
#override
double get maxExtent => 300;
#override
double get minExtent => 80;
#override
bool shouldRebuild(SliverPersistentHeaderDelegate oldDelegate) => true;
}