scrolling to the top when typing on TextField on Flutter - flutter

Question

I added TextFormField on SliverPersistentHeaderDelegate. After scroll to the middle/bottom and then typing on to the textField, SliverList automatically come to the top. How do I disable this?
Full Code.
class MyWidget extends StatelessWidget {
static const String route = '/myWidget';
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
child: CustomScrollView(
slivers: <Widget>[
SliverPersistentHeader(
pinned: true,
delegate: MyDynamicHeader(),
),
SliverList(
delegate: SliverChildBuilderDelegate((BuildContext context, int index) {
return Container(
height: 200,
color: Color(Random().nextInt(0xffffffff)),
);
},
)
)
],
)
)
);
}
}
class MyDynamicHeader extends SliverPersistentHeaderDelegate {
int index = 0;
#override
Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
return LayoutBuilder(
builder: (context, constraints) {
final Color color = Colors.primaries[index];
final double percentage = (constraints.maxHeight - minExtent)/(maxExtent - minExtent);
if (++index > Colors.primaries.length-1)
index = 0;
return Container(
decoration: BoxDecoration(
boxShadow: [BoxShadow(blurRadius: 4.0, color: Colors.black45)],
gradient: LinearGradient(
colors: [Colors.blue, color]
)
),
height: constraints.maxHeight,
child: SafeArea(
child: Center(
child: Row(
children: <Widget>[
CircularProgressIndicator(
value: percentage,
valueColor: AlwaysStoppedAnimation<Color>(Colors.white),
),
InkWell(
onTap: (){
print('is working');
},
child: Container(
height: 50,
width: 100,
color: Palette.orelPay,
),
),
Expanded(child: TextFormField(
//controller: searchController,
decoration: InputDecoration(
contentPadding:
EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
hintText: "Search on OrelBuy",
border: OutlineInputBorder(
borderSide:
BorderSide(color: Palette.background, width: 32.0),
borderRadius: BorderRadius.circular(50.0)),
fillColor: Palette.background,
filled: true,
enabledBorder: OutlineInputBorder(
borderSide:
BorderSide(color: Palette.background, width: 32.0),
borderRadius: BorderRadius.circular(50.0)),
focusedBorder: OutlineInputBorder(
borderSide:
BorderSide(color: Palette.background, width: 32.0),
borderRadius: BorderRadius.circular(50.0))),
),)
],
),
)
),
);
}
);
}
#override
bool shouldRebuild(SliverPersistentHeaderDelegate old) => false;
#override
double get maxExtent => 250.0;
#override
double get minExtent => 80.0;
}

Answer 1

you can use physics of CustomScrollView widget to control scroll.
CustomScrollView(
physics: PageScrollPhysics(), // added
slivers: <Widget>[