库 extended_nested_scroll_view

https://pub.dev/packages/extended_nested_scroll_view
中文说明：https://github.com/fluttercandies/extended_nested_scroll_view/blob/master/README-ZH.md

扩展NestedScrollView来修复了下面的问题
1.pinned的Header的问题
2.body里面TabView列表滚动同步，互相影响的问题
3.下拉刷新不能工作
4.在NestedScrollView的body中不通过设置ScrollController(设置了会跟内部Controller冲突)来完成下拉刷新，增量加载，滚动到顶部

• Flutter 扩展NestedScrollView （一）Pinned头引起的bug解决
• Flutter 扩展NestedScrollView （二）列表滚动同步解决
• Flutter 扩展NestedScrollView （三）下拉刷新的解决

安装依赖

dependencies:
  extended_nested_scroll_view: ^2.0.0

导入

import 'package:extended_nested_scroll_view/extended_nested_scroll_view.dart';

示例

import 'dart:async';
import 'package:app1/utils/Base.dart';
import 'package:flutter/material.dart';
import 'package:flutter_easyrefresh/easy_refresh.dart';
import 'package:extended_nested_scroll_view/extended_nested_scroll_view.dart' as extended;
class NestedScrollViewPage extends StatefulWidget {
  @override
  _NestedScrollViewPageState createState() => _NestedScrollViewPageState();
}
class _NestedScrollViewPageState extends State<NestedScrollViewPage>
    with SingleTickerProviderStateMixin {
  TabController _tabController; //tab控制器
  int _tabIndex = 0; //Tab索引
  int _listCount = 10; //tab-列表数量
  int _gridCount = 10; //tab-表格数量
  @override
  void initState() {
    super.initState();
    _tabController = TabController(length: 2, vsync: this);
  }
  @override
  void dispose() {
    super.dispose();
    _tabController.dispose();
  }
  @override
  Widget build(BuildContext context) {
    // 在NestedScrollView当中，有2个ScrollController.
    // 一个是inner，一个outer。
    // outer是负责headerSliverBuilder里面的滚动widgets
    // inner是负责body里面的滚动widgets 当outer滚动到底了之后，就会看看inner里面是否有能滚动的东东，开始滚动。
    return extended.NestedScrollView(
      // 在pinnedHeaderSliverHeightBuilder回调中设置全部pinned的header的高度，
      // demo里面高度为 状态栏高度+SliverAppbar的高度
      pinnedHeaderSliverHeightBuilder: () {
        return MediaQuery.of(context).padding.top + kToolbarHeight;
      },
      // innerScrollPositionKeyBuilder回调中给出当前tab的key.
      innerScrollPositionKeyBuilder: () {
        if (_tabController.index == 0) {
          return Key('tab0');
        } else {
          return Key('tab1');
        }
      },
      headerSliverBuilder: (context, innerBoxIsScrolled) {
        return [
          SliverAppBar(
            title: Text("NestedScrollView"),
            pinned: true,
            expandedHeight: 120.0,
            flexibleSpace: SingleChildScrollView(
              physics: NeverScrollableScrollPhysics(),
              child: Container(),
            ),
            floating: false,
          ),
        ];
      },
      body: Column(
        children: [
          Container(
            height: 50,
            color: Colors.green,
            child: TabBar(
              controller: _tabController,
              onTap: (index) {
                setState(() {
                  _tabIndex = index;
                });
              },
              tabs: [
                Tab(text: 'List'),
                Tab(text: 'Grid'),
              ],
            ),
          ),
          Expanded(
            child: IndexedStack(
              index: _tabIndex,
              children: [
                // TabbarView里面的列表，使用NestedScrollViewInnerScrollPositionKeyWidget包住，
                // 并且设置唯一key， 这个key跟列表是第几个tab有关系。
                extended.NestedScrollViewInnerScrollPositionKeyWidget(
                  Key('Tab0'),
                  EasyRefresh(
                    child: ListView.builder(
                      padding: EdgeInsets.all(0.0),
                      itemBuilder: (context, index) {
                        return Container(
                          color: Color(Base.getRandomColor()),
                          height: 100,
                          child: Text('我是列表文本 ${index + 1}', textScaleFactor: 3),
                        );
                      },
                      itemCount: _listCount,
                    ),
                    onRefresh: () async {
                      await Future.delayed(Duration(seconds: 2), () {
                        if (mounted) {
                          setState(() {
                            _listCount = 10;
                          });
                        }
                      });
                    },
                    onLoad: () async {
                      await Future.delayed(Duration(seconds: 2), () {
                        if (mounted) {
                          setState(() {
                            _listCount += 10;
                          });
                        }
                      });
                    },
                  ),
                ),
                extended.NestedScrollViewInnerScrollPositionKeyWidget(
                  Key('Tab1'),
                  EasyRefresh(
                    child: GridView.builder(
                      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                        crossAxisCount: 2,
                        childAspectRatio: 6 / 7,
                      ),
                      itemBuilder: (context, index) {
                        return Container(
                          color: Color(Base.getRandomColor()),
                          height: 100,
                          child: Text('我是表格文本 ${index + 1}', textScaleFactor: 2),
                        );
                      },
                      itemCount: _gridCount,
                    ),
                    onRefresh: () async {
                      await Future.delayed(Duration(seconds: 2), () {
                        if (mounted) {
                          setState(() {
                            _gridCount = 10;
                          });
                        }
                      });
                    },
                    onLoad: () async {
                      await Future.delayed(Duration(seconds: 2), () {
                        if (mounted) {
                          setState(() {
                            _gridCount += 10;
                          });
                        }
                      });
                    },
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}