Flutter-动画完成后滚动

Question

我已使用补间动画在容器中使用自定义应用栏设计了此布局，以实现所示效果。

通过以下代码-

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NestedScrollView(
        headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
          return [
            TransitionAppBar(
                title: Container(
                    margin: EdgeInsets.symmetric(horizontal: 20.0, vertical: 0),
                    decoration: BoxDecoration(
                        color: Colors.grey[200],
                        borderRadius: BorderRadius.all(Radius.circular(5.0))),
                    child: Row(children: <Widget>[
                      Padding(
                          padding: EdgeInsets.only(left: 20.0, right: 10.0),
                          child: Icon(Icons.search)),
                      Expanded(
                          child: TextFormField(
                              decoration: InputDecoration(
                                  hintText: "Search",
                                  border: InputBorder.none)))
                    ])))
          ];
        },
        body: ListView.builder(
          itemBuilder: (BuildContext context, int index) {
            return ListTile(
              title: Text("${index}"),
            );
          },
        ),
      ),
    );
  }

class TransitionAppBar extends StatelessWidget {
  final Widget title;

  const TransitionAppBar({this.title, Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SliverPersistentHeader(
        pinned: true, delegate: _TransitionAppBarDelegate(title: title));
  }
}

class _TransitionAppBarDelegate extends SliverPersistentHeaderDelegate {
  final _titleMarginTween = EdgeInsetsTween(
    begin: EdgeInsets.only(top: 100.0 + 5.0),
    end: EdgeInsets.only(top: 10.0 + 50.0 + 5.0),
  );
  final _titleAlignTween =
      AlignmentTween(begin: Alignment.center, end: Alignment.topCenter);

  final Widget title;

  _TransitionAppBarDelegate({this.title}) : assert(title != null);

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    final progress = shrinkOffset / 200.0;

    final titleMargin = _titleMarginTween.lerp(progress);
    final titleAlign = _titleAlignTween.lerp(progress);
    return Stack(
      children: <Widget>[
        AnimatedContainer(
          duration: Duration(milliseconds: 100),
          height: progress * 110,
          color: Colors.redAccent,
        ),
        Padding(
          padding: titleMargin,
          child: Align(
            alignment: titleAlign,
            child: title,
          ),
        )
      ],
    );
  }

  @override
  double get maxExtent => 180.0;

  @override
  double get minExtent => 150.0;

  @override
  bool shouldRebuild(_TransitionAppBarDelegate oldDelegate) {
    return title != oldDelegate.title;
  }
}

此代码可以正常工作，但是目前您可以在下面的屏幕截图中看到，列表的第一个元素（即0）位于搜索文本表单字段的后面。 但是我要实现的是在Transition App Bar动画完成后滚动列表。