[英]Exception Caught By Widgets Library error in Flutter
我在 Flutter 中有这个应用程序。它有两个类可以生成笔记列表。
这是主 class,MyApp class:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:notesgenerator/sala.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
List<Sala> locs = [
Sala(note: 'Study', noteDes: 'from 6pm ~ 8pm'),
Sala(note: 'Work', noteDes: 'from 8pm ~ 9pm'),
Sala(note: 'Play', noteDes: 'from 9pm ~ 9:30pm'),
Sala(note: 'Eat', noteDes: 'from 9:30pm ~ 10pm'),
];
return Scaffold(
appBar: AppBar(
title: Text('NoteIndex'),
centerTitle: true,
),
body: ListView.builder(
itemCount: 10,
itemBuilder: (context, index) {
return Card(
child: ListTile(
onTap: () {},
title: (Text(locs[index].note)),
),
);
}),
);}}
这是存储数据的class,Sala class:
class Sala {
String note;
String noteDes;
Sala({this.note, this.noteDes});
}
当我尝试运行它时,我得到这个:
I/flutter (21388): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (21388): The following assertion was thrown building MyApp:
I/flutter (21388): MediaQuery.of() called with a context that does not contain a MediaQuery.
I/flutter (21388): No MediaQuery ancestor could be found starting from the context that was passed to MediaQuery.of().
I/flutter (21388): This can happen because you do not have a WidgetsApp or MaterialApp widget (those widgets introduce
I/flutter (21388): a MediaQuery), or it can happen if the context you use comes from a widget above those widgets.
I/flutter (21388): The context used was:
I/flutter (21388): Scaffold
I/flutter (21388):
I/flutter (21388): The relevant error-causing widget was:
I/flutter (21388): MyApp file:///F:/FlutterProjects/notesgenerator/lib/main.dart:6:23
I/flutter (21388):
I/flutter (21388): When the exception was thrown, this was the stack:
I/flutter (21388): #0 MediaQuery.of (package:flutter/src/widgets/media_query.dart:798:5)
I/flutter (21388): #1 ScaffoldState.didChangeDependencies (package:flutter/src/material/scaffold.dart:1993:50)
I/flutter (21388): #2 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4376:12)
I/flutter (21388): #3 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
I/flutter (21388): #4 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter (21388): #5 Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter (21388): #6 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4243:16)
I/flutter (21388): #7 Element.rebuild (package:flutter/src/widgets/framework.dart:3947:5)
I/flutter (21388): #8 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5)
I/flutter (21388): #9 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
I/flutter (21388): #10 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
I/flutter (21388): #11 Element.updateChild (package:flutter/src/widgets/framework.dart:2988:12)
I/flutter (21388): #12 RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1028:16)
I/flutter (21388): #13 RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:999:5)
I/flutter (21388): #14 RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:942:17)
I/flutter (21388): #15 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2412:19)
I/flutter (21388): #16 RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:941:13)
I/flutter (21388): #17 WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:819:7)
I/flutter (21388): #18 WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:804:7)
I/flutter (21388): #27 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:384:19)
I/flutter (21388): #28 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:418:5)
I/flutter (21388): #29 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:174:12)
I/flutter (21388): (elided 8 frames from package dart:async and package dart:async-patch)
I/flutter (21388):
I/flutter (21388): ════════════════════════════════════════════════════════════════════════════════════════════════════
如果您能提供帮助,我将不胜感激,如果您有任何疑问,请在评论中告诉我!
用 MaterialApp 包裹你的脚手架
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: Scaffold(),
);
你需要用包裹你的脚手架
材质应用程序()
因为这是引入MediaQuery的widget
MyApp 构建的变化:
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: Scaffold(
...
),
);
解决方案
itemCount: locs.length
而不是itemCount: 10
。
对于那些对原因感到好奇的人,请阅读以下内容:
看看你的清单:
List<Sala> locs = [
Sala(note: 'Study', noteDes: 'from 6pm ~ 8pm'),
Sala(note: 'Work', noteDes: 'from 8pm ~ 9pm'),
Sala(note: 'Play', noteDes: 'from 9pm ~ 9:30pm'),
Sala(note: 'Eat', noteDes: 'from 9:30pm ~ 10pm'),
];
很明显,您的列表长度为 3。
但是,在您的ListViewBuilder中:
itemCount: 10,
您正在设置一个 static 值为 10,这将告诉构建器有 10 个项目要返回,并且超出了您列表的实际长度,明确表示,您正在返回 10 个 Card 项目,而您的列表仅包含 3 个项目,这将尝试创建 10 个从列表开始时不存在的项目,当然当迭代器返回列表的最后一个项目时它会返回索引错误,这意味着它将返回错误第 4 个索引,因为您只有 3 个项目。
如果您使用的是 Getxbuilder,请遵循以下说明:
首先,您必须验证每个 Getxbuilder 视图的 Getxbuilder<YOUR_VIEW_CONTROLER> 名称 controller。
这是我收到错误时唯一的问题。
按照代码:
GetBuilder<**RecentMatchListViewController**>(
builder: (_) => recentMatchListViewController!
.recentMatchListModel!
.data![index]
.result ==
null
? progressIndicator(1)
: Text(
recentMatchListViewController!
.recentMatchListModel!
.data![index]
.result
.toString(),
style: redHeadingTextStyle(),
textAlign: TextAlign.center,
),
)
RecentMatchListViewController 可能会更改为另一个视图 controller,例如
GetBuilder<**UpcomingMatchListViewController**>(
builder: (_) => recentMatchListViewController!
.recentMatchListModel!
.data![index]
.result ==
null
? progressIndicator(1)
: Text(
recentMatchListViewController!
.recentMatchListModel!
.data![index]
.result
.toString(),
style: redHeadingTextStyle(),
textAlign: TextAlign.center,
),
)
这是由于一些复制过去的工作,并且还通过不匹配导入了文件。
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