如果头部内容比较多的时候，下拉刷新，会导致TabBar触碰屏幕底部，这个时候报错了

[winter-tech]

          > 

如果头部内容比较多的时候，下拉刷新，会导致TabBar触碰屏幕底部，这个时候报错了：

The following assertion was thrown during layout:
A RenderFlex overflowed by 2.2 pixels on the bottom.
The relevant error-causing widget was:
  Column


The overflowing RenderFlex has an orientation of Axis.vertical.
The edge of the RenderFlex that is overflowing has been marked in the rendering with a yellow and
black striped pattern. This is usually caused by the contents being too big for the RenderFlex.
Consider applying a flex factor (e.g. using an Expanded widget) to force the children of the
RenderFlex to fit within the available space instead of being sized to their natural size.
This is considered an error condition because it indicates that there is content that cannot be
seen. If the content is legitimately bigger than the available space, consider clipping it with a
ClipRect widget before putting it in the flex, or using a scrollable container rather than a Flex,
like a ListView.
The specific RenderFlex in question is: RenderFlex#5b952 OVERFLOWING:
  needs compositing
  creator: Column ← PrimaryScrollController ← _ExtendedSliverFillRemainingWithScrollable ←
    NestedScrollViewViewport ← IgnorePointer-[GlobalKey#6a289] ← Semantics ← Listener ←
    _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#f88cd] ←
    Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#23cd8] ← ⋯
  parentData: paintOffset=Offset(0.0, -0.0)
  constraints: BoxConstraints(w=360.0, h=45.8)
  size: Size(360.0, 45.8)
  direction: vertical
  mainAxisAlignment: start
  mainAxisSize: max
  crossAxisAlignment: center
  verticalDirection: down

完整代码：

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:easy_refresh/easy_refresh.dart';
import 'package:extended_nested_scroll_view/extended_nested_scroll_view.dart';

class TabBarViewPage extends StatefulWidget {
  const TabBarViewPage({Key? key}) : super(key: key);

  @override
  TabBarViewPageState createState() {
    return TabBarViewPageState();
  }
}

class TabBarViewPageState extends State<TabBarViewPage>
    with SingleTickerProviderStateMixin {
  late TabController _tabController;
  int _listCount = 20;
  int _gridCount = 20;

  @override
  void initState() {
    super.initState();
    _tabController = TabController(length: 2, vsync: this);
  }

  @override
  void dispose() {
    super.dispose();
    _tabController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final themeData = Theme.of(context);
    return Scaffold(
      body: EasyRefresh.builder(
        header: ClassicHeader(
          clamping: true,
          position: IndicatorPosition.locator,
          mainAxisAlignment: MainAxisAlignment.end,
          dragText: 'Pull to refresh',
          armedText: 'Release ready',
          readyText: 'Refreshing...',
          processingText: 'Refreshing...',
          processedText: 'Succeeded',
          noMoreText: 'No more',
          failedText: 'Failed',
          messageText: 'Last updated at %T',
        ),
        footer: ClassicFooter(
          position: IndicatorPosition.locator,
          dragText: 'Pull to load',
          armedText: 'Release ready',
          readyText: 'Loading...',
          processingText: 'Loading...',
          processedText: 'Succeeded',
          noMoreText: 'No more',
          failedText: 'Failed',
          messageText: 'Last updated at %T',
        ),
        onRefresh: () async {
          await Future.delayed(const Duration(seconds: 2), () {
            if (mounted) {
              setState(() {
                if (_tabController.index == 0) {
                  _listCount = 20;
                } else {
                  _gridCount = 20;
                }
              });
            }
          });
        },
        onLoad: () async {
          await Future.delayed(const Duration(seconds: 2), () {
            if (mounted) {
              setState(() {
                if (_tabController.index == 0) {
                  _listCount += 10;
                } else {
                  _gridCount += 10;
                }
              });
            }
          });
        },
        childBuilder: (context, physics) {
          return ScrollConfiguration(
            behavior: const ERScrollBehavior(),
            child: ExtendedNestedScrollView(
              physics: physics,
              onlyOneScrollInBody: true,
              pinnedHeaderSliverHeightBuilder: () {
                return MediaQuery.of(context).padding.top + kToolbarHeight;
              },
              headerSliverBuilder: (context, innerBoxIsScrolled) {
                return <Widget>[
                  const HeaderLocator.sliver(clearExtent: false),
                  SliverAppBar(
                    expandedHeight: 120,
                    pinned: true,
                    flexibleSpace: FlexibleSpaceBar(
                      title: Text(
                        'TabBarView',
                        style: TextStyle(
                            color:
                            Theme.of(context).textTheme.titleLarge?.color),
                      ),
                      centerTitle: false,
                    ),
                  ),
                  SliverToBoxAdapter(
                    child: Container(
                      height: 500,
                      color: Colors.green,
                      child: const Text('其他内容'),
                    ),
                  )
                ];
              },
              body: Column(
                children: [
                  TabBar(
                    controller: _tabController,
                    labelColor: themeData.colorScheme.primary,
                    indicatorColor: themeData.colorScheme.primary,
                    tabs: const <Widget>[
                      Tab(
                        text: 'List',
                      ),
                      Tab(
                        text: 'Grid',
                      ),
                    ],
                  ),
                  Expanded(
                    child: TabBarView(
                      controller: _tabController,
                      children: <Widget>[
                        ExtendedVisibilityDetector(
                          uniqueKey: const Key('Tab0'),
                          child: _AutomaticKeepAlive(
                            child: CustomScrollView(
                              physics: physics,
                              slivers: [
                                SliverList(
                                    delegate: SliverChildBuilderDelegate(
                                            (context, index) {
                                          return SizedBox(
                                            height: 60,
                                            child: Text(index.toString()),
                                          );
                                        }, childCount: _listCount)),
                                const FooterLocator.sliver(),
                              ],
                            ),
                          ),
                        ),
                        ExtendedVisibilityDetector(
                          uniqueKey: const Key('Tab1'),
                          child: _AutomaticKeepAlive(
                            child: CustomScrollView(
                              physics: physics,
                              slivers: [
                                SliverGrid(
                                    delegate: SliverChildBuilderDelegate(
                                            (context, index) {
                                          return SizedBox(
                                            height: 60,
                                            child: Text(index.toString()),
                                          );
                                        }, childCount: _gridCount),
                                    gridDelegate:
                                    const SliverGridDelegateWithFixedCrossAxisCount(
                                      crossAxisCount: 2,
                                      childAspectRatio: 6 / 7,
                                    )),
                                const FooterLocator.sliver(),
                              ],
                            ),
                          ),
                        ),
                      ],
                    ),
                  ),
                ],
              ),
            ),
          );
        },
      ),
    );
  }
}

class _AutomaticKeepAlive extends StatefulWidget {
  final Widget child;

  const _AutomaticKeepAlive({
    Key? key,
    required this.child,
  }) : super(key: key);

  @override
  State<_AutomaticKeepAlive> createState() => _AutomaticKeepAliveState();
}

class _AutomaticKeepAliveState extends State<_AutomaticKeepAlive>
    with AutomaticKeepAliveClientMixin {
  @override
  Widget build(BuildContext context) {
    super.build(context);
    return widget.child;
  }

  @override
  bool get wantKeepAlive => true;
}

Originally posted by @lan2000 in #508 (comment)