如何在颤动中滚动时固定SliverAppBar中的TextField？

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: CustomScrollView(
          slivers: <Widget>[
            SliverAppBar(
              pinned: true,
              expandedHeight: 200,
              flexibleSpace: FlexibleSpaceBar(
                title: Text('Scrolling TextField'),
              ),
              bottom: PreferredSize(
                preferredSize: Size.fromHeight(48),
                child: SliverPersistentHeader(
                  delegate: _TextFieldDelegate(),
                ),
              ),
            ),
            SliverList(
              delegate: SliverChildBuilderDelegate(
                (context, index) => ListTile(
                  title: Text('Item $index'),
                ),
                childCount: 100,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class _TextFieldDelegate extends SliverPersistentHeaderDelegate {
  @override
  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Container(
      color: Colors.white,
      child: TextField(
        decoration: InputDecoration(
          hintText: 'Enter text',
          contentPadding: EdgeInsets.all(16),
        ),
      ),
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}