Flutter sliver + tabBar + smartRefresh

源码：

import 'dart:math';
import 'package:flutter/widgets.dart';
import 'package:provider/provider.dart';
import 'package:flutter/material.dart';
import 'package:pull_to_refresh/pull_to_refresh.dart';
import 'package:***/common/widgets/nomultiges.dart';
import 'package:***/common/widgets/refreshwidget.dart';
import 'package:***/generated/l10n.dart';
import 'package:***/module/session/provider/backlog_provider.dart';
import '/basic/basic_header.dart';

class BacklogPage extends StatefulWidget {
  @override
  _BacklogPageState createState() => _BacklogPageState();
}

class _BacklogPageState extends State {
  @override
  Widget build(BuildContext context) {
    return Store.init(
      providers: [ChangeNotifierProvider(create: (ctx) => BacklogProvider())],
      child: Scaffold(
        body: _Content(),
        appBar: appBar(context,title: S.current.backlog,actions: [_SortButton()]),
      ),
    );
  }
}

class _SortButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return NoMultiGes(
      child: Container(
        width: 56,
        height: 56,
        color: Colors.transparent,
        alignment: Alignment.center,
        child: Transform.rotate(
          angle: pi/2,
          child: Image.asset(
            R.assetsImgCommonMore,
            width: 56.fitWidth(),
            height: 56.fitWidth(),
          ),
        ),
      ),
      onTap: _clickedAction(),
    );
  }

  _clickedAction() {

  }
}

class _Content extends StatefulWidget{
  @override
  State createState() => _ContentState();
}

class _ContentState extends State<_Content> {

  RefreshController _refreshController = RefreshController();

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
        length: 3,
        initialIndex: 1,
        child: NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            return [
              _searchBar(),
              _tabBar(),
            ];
          },
          body: TabBarView(
            children: [
              Container(width: double.infinity,height: 200,color: Colors.cyan,),
              Container(width: double.infinity,height: 400,color: Colors.purple,),
              RefreshWidget(
                controller: _refreshController,
                onRefresh: _refreshAction,
                child: ListView.builder(
                  itemCount: 30,
                  itemBuilder: (ctx,index) {
                    return Container(
                      height: 50,
                      color: index % 2 == 0 ? Colors.white : Colors.black12,
                      width: double.infinity,
                      alignment: Alignment.center,
                      child: Text("我是第${index}个item"),
                    );
                  },
                ),
              ),
            ],
          )
        ),
    );
  }

  Widget _searchBar() {
    return SliverToBoxAdapter(
      child: Container(height: 44,width: double.infinity,color: Colors.amberAccent,),
    );
  }

  Widget _tabBar() {
    return SliverPersistentHeader(
      pinned: true, //是否固定在顶部
      floating: true,
      delegate: _SliverAppBarDelegate(
          minHeight: 50, //收起的高度
          maxHeight: 50, //展开的最大高度
          child: Row(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              Flexible(
                fit: FlexFit.tight,
                child: TabBar(
                  tabs: [
                    Tab(
                      text: "Tab1",
                    ),
                    Tab(
                      text: "Tab2",
                    ),
                    Tab(
                      text: "Tab3",
                    ),
                  ],
                  isScrollable: false,
                  indicatorSize: TabBarIndicatorSize.label,
                  labelColor: Colors.black87,
                  unselectedLabelColor: Colors.grey,
                ),
              ),
              Container(
                width: 80,
                color: Colors.blueAccent,
              )
            ],
          ),
      ),
    );
  }


  _refreshAction() {
    _refreshController.refreshCompleted();
  }

}

class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  _SliverAppBarDelegate({
    required this.minHeight,
    required this.maxHeight,
    required this.child,
  });

  final double minHeight;
  final double maxHeight;
  final Widget child;

  @override
  double get minExtent => minHeight;

  @override
  double get maxExtent => max(maxHeight, minHeight);

  @override
  Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Container(color: Colors.white,child: child,);
  }

  @override
  bool shouldRebuild(_SliverAppBarDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}