标签栏内容在创建带有标签的折叠工具栏时向上滚动直到状态栏

如何解决标签栏内容在创建带有标签的折叠工具栏时向上滚动直到状态栏

我正在尝试实现带有标签的折叠工具栏。滚动选项卡的内容时，不会停留在选项卡的底部，而是向上滚动直到状态栏。

我不确定我到底在做什么错。我想得到您的帮助来解决此问题。

这是代码段：

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:mobile/src/data/model/order_response.dart';
import 'package:mobile/src/widget/order_view.dart';

class OrderDetailPage extends StatefulWidget {
  final OrderResponse item;

  OrderDetailPage(this.item);

  @override
  _OrderDetailPageState createState() => _OrderDetailPageState();
}

class _OrderDetailPageState extends State<OrderDetailPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: DefaultTabController(
        length: 2,child: NestedScrollView(
            headerSliverBuilder:
                (BuildContext context,bool innerBoxIsScrolled) {
              return <Widget>[
                SliverAppBar(
                  backgroundColor: Colors.black12,elevation: 0.0,expandedHeight: 230,floating: false,pinned: true,flexibleSpace: FlexibleSpaceBar(
                    collapseMode: CollapseMode.parallax,background: Align(
                      alignment: Alignment.bottomCenter,child: Container(
                        child: Column(
                          children: [
                            SizedBox(
                              height: 90,),OrderListItemView(widget.item,null)
                          ],SliverPersistentHeader(
                  pinned: true,delegate: _SliverAppBarDelegate(
                    TabBar(
                      labelColor: Colors.black87,unselectedLabelColor: Colors.grey,tabs: [
                        new Tab(text: "Instant Match"),new Tab(text: "Requests"),],)
              ];
            },body: new TabBarView(
              children: <Widget>[
                Text(
                  'This content should stick to the bottom of tab bar',style: TextStyle(fontSize: 24),Text('This content should stick to the bottom of tab bar')
              ],)),);
  }

  void _onClickMenu(String value) {}
}

class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  _SliverAppBarDelegate(this._tabBar);

  final TabBar _tabBar;

  @override
  double get minExtent => _tabBar.preferredSize.height;

  @override
  double get maxExtent => _tabBar.preferredSize.height;

  @override
  Widget build(
      BuildContext context,double shrinkOffset,bool overlapsContent) {
    return new Container(
      child: _tabBar,);
  }

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

电流输出：

在所需的输出中，内容应粘贴在标签栏的底部。