flutter - Flutter NestedScrollView 错误:断言失败:第 4944 行 pos 14:'_dependents.isEmpty':不正确
问题描述
我正在尝试使用 NestedScrollView,但遇到了问题。我已将代码简化为这个简单的示例,展示了这个问题。
var tabs = ['Tab1', 'Tab2', 'Tab3'];
@override
Widget build(BuildContext context) {
return DefaultTabController(
length: 3,
child: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
SliverAppBar(
pinned: true,
expandedHeight: 200.0,
bottom: TabBar(
tabs: tabs.map((tab) => Tab(text: tab)).toList(),
),
)
];
},
body: TabBarView(
children: [
_wrapTabWidget(Text('Tab 1')),
_wrapTabWidget(Text('Tab 2')),
_wrapTabWidget(Text('Tab 3'))
],
),
),
);
}
_wrapTabWidget(tabWidget) {
return Builder(
builder: (BuildContext context) {
return CustomScrollView(
slivers: <Widget>[
SliverOverlapInjector(
handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
),
tabWidget
],
);
},
);
}
我得到的错误是:
'package:flutter/src/widgets/framework.dart': Failed assertion: line 4944 pos 14: '_dependents.isEmpty': is not true.
The relevant error-causing widget was:
NestedScrollView
我以前没有使用过 NestedScrollView,所以我假设我缺少一些简单的东西,但我不确定是什么。
解决方案
您可以在下面复制粘贴运行完整代码
第 1 步:您需要SliverOverlapAbsorber
第SliverOverlapInjector
2 步:您需要SliverToBoxAdapter
,SliverToBoxAdapter
是一个包含单个框小部件的条子。
代码片段
_wrapTabWidget(tabWidget2(Text("Tab1"))),
Widget tabWidget2(Text text) {
return SliverToBoxAdapter(
child: text,
);
}
工作演示
完整代码
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
List<String> tabs = ['Tab1', 'Tab2', 'Tab3'];
@override
Widget build(BuildContext context) {
return Scaffold(
body: DefaultTabController(
length: tabs.length, // This is the number of tabs.
child: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return <Widget>[
SliverOverlapAbsorber(
handle:
NestedScrollView.sliverOverlapAbsorberHandleFor(context),
sliver: SliverAppBar(
title: const Text('Books'),
pinned: true,
expandedHeight: 200.0,
forceElevated: innerBoxIsScrolled,
bottom: TabBar(
// These are the widgets to put in each tab in the tab bar.
tabs: tabs.map((String name) => Tab(text: name)).toList(),
),
),
),
];
},
body: TabBarView(
children: [
_wrapTabWidget(tabWidget2(Text("Tab1"))),
_wrapTabWidget(tabWidget2(Text("Tab2"))),
_wrapTabWidget(tabWidget2(Text("Tab3"))),
],
),
),
),
);
}
Widget tabWidget2(Text text) {
return SliverToBoxAdapter(
child: text,
);
}
_wrapTabWidget(tabWidget) {
return Builder(
builder: (BuildContext context) {
return CustomScrollView(
slivers: <Widget>[
SliverOverlapInjector(
handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
),
tabWidget
],
);
},
);
}
}
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