scrollPercentage only 0 or 1

[mwinfomatica]

My scrollPercentage gets only 0 or 1.

%Cblue class Body extends StatelessWidget {

@OverRide
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: CustomScrollView(
slivers: [
SliverStickyHeader.builder(
builder: (context, state) => Container(
height: 60.0,
color: (state.isPinned ? Colors.pink : Colors.lightBlue)
.withOpacity(1.0 - state.scrollPercentage),
padding: EdgeInsets.symmetric(horizontal: 16.0),
alignment: Alignment.centerLeft,
child: Text(
'Header #1',
style: const TextStyle(color: Colors.white),
),
),
sliver: SliverList(
delegate: SliverChildBuilderDelegate(
(context, i) => ListTile(
leading: CircleAvatar(
child: Text('0'),
),
title: Text('List tile #$i'),
),
childCount: 4,
),
),
),
],
),
),
);
}
}

[letsar]

If you look at the example, it varies from 0 to 1. Can you provide a complete example I could just copy/paste and run to test?