即使有可用空间，NestedScrollView主体也会继续滚动

Question

我的要求是创建一个带有折叠的工具栏和两个选项卡的页面。为此，我使用下面的代码。

SafeArea(
        child: DefaultTabController(
          length: 2,
          child: NestedScrollView(
            headerSliverBuilder:
                (BuildContext context, bool innerBoxIsScrolled) {
              return [
                SliverPersistentHeader(
                  pinned: true,
                  delegate: _Header(),
                )
              ];
            },
            body: TabBarView(
              children: <Widget>[
                Container1(),
                Container2(),
              ],
            ),
          ),
        ),
      )

一切正常，但是一旦开始滚动并且页眉折叠，即使所有小部件都可见，主体也会继续滚动。

我如何使其表现得像Android本机，如果列表很小，则在标题折叠后列表不会滚动。

Answer 1

对于面临相同问题的任何人，这就是我解决的方法。您可以复制整个代码并运行它以进行检查和修改。该代码取自官方documentation。

import 'dart:convert';
import 'dart:math';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:flutter_module/app_constants.dart';
import 'package:flutter_module/data/local/shared_pref.dart';
import 'package:flutter_module/data/remote/api_end_points.dart';
import 'package:flutter_module/string_localization.dart';
import 'package:flutter_module/ui/router.dart';
import 'package:flutter_module/util.dart';
import 'package:http/http.dart' as http;

import 'data/local/dao/sync_dao.dart';
import 'data/remote/response_pojo/video_challenges_response.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MainCollapsingToolbar(),
    );
  }
}

class MainCollapsingToolbar extends StatefulWidget {
  @override
  _MainCollapsingToolbarState createState() => _MainCollapsingToolbarState();
}

class _MainCollapsingToolbarState extends State<MainCollapsingToolbar> {
  @override
  Widget build(BuildContext context) {
    var _tabs = ["One", "Two"];
    return Scaffold(
      body: DefaultTabController(
        length: _tabs.length, // This is the number of tabs.
        child: NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            // These are the slivers that show up in the "outer" scroll view.
            return <Widget>[
              SliverOverlapAbsorber(
                // This widget takes the overlapping behavior of the SliverAppBar,
                // and redirects it to the SliverOverlapInjector below. If it is
                // missing, then it is possible for the nested "inner" scroll view
                // below to end up under the SliverAppBar even when the inner
                // scroll view thinks it has not been scrolled.
                // This is not necessary if the "headerSliverBuilder" only builds
                // widgets that do not overlap the next sliver.
                handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                child: SliverPersistentHeader(
                  pinned: true,
                  delegate: _SliverAppBarDelegate(minHeight: 100, maxHeight: 150, child: Container(
                    color: Colors.blue,
                  )),
                ),
              ),
            ];
          },
          body: TabBarView(
            // These are the contents of the tab views, below the tabs.
            children: _tabs.map((String name) {
              return SafeArea(
                top: false,
                bottom: false,
                child: Builder(
                  // This Builder is needed to provide a BuildContext that is
                  // "inside" the NestedScrollView, so that
                  // sliverOverlapAbsorberHandleFor() can find the
                  // NestedScrollView.
                  builder: (BuildContext context) {
                    return CustomScrollView(
                      // The "controller" and "primary" members should be left
                      // unset, so that the NestedScrollView can control this
                      // inner scroll view.
                      // If the "controller" property is set, then this scroll
                      // view will not be associated with the NestedScrollView.
                      // The PageStorageKey should be unique to this ScrollView;
                      // it allows the list to remember its scroll position when
                      // the tab view is not on the screen.
                      key: PageStorageKey<String>(name),
                      slivers: <Widget>[
                        SliverOverlapInjector(
                          // This is the flip side of the SliverOverlapAbsorber
                          // above.
                          handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                        ),
                        SliverPadding(
                          padding: const EdgeInsets.all(8.0),
                          // In this example, the inner scroll view has
                          // fixed-height list items, hence the use of
                          // SliverFixedExtentList. However, one could use any
                          // sliver widget here, e.g. SliverList or SliverGrid.
                          sliver: SliverFixedExtentList(
                            // The items in this example are fixed to 48 pixels
                            // high. This matches the Material Design spec for
                            // ListTile widgets.
                            itemExtent: 48.0,
                            delegate: SliverChildBuilderDelegate(
                                  (BuildContext context, int index) {
                                // This builder is called for each child.
                                // In this example, we just number each list item.
                                return ListTile(
                                  title: Text('Item $index'),
                                );
                              },
                              // The childCount of the SliverChildBuilderDelegate
                              // specifies how many children this inner list
                              // has. In this example, each tab has a list of
                              // exactly 30 items, but this is arbitrary.
                              childCount: 1,
                            ),
                          ),
                        ),
                      ],
                    );
                  },
                ),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}