Exception Caught By Widgets Library error in Flutter

Question

I have this application in Flutter. It has two classes it spouses to generate a list of notes.

This is the main class, the 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)),
              ),
            );
          }),
    );}}

This is the class that stores the data, the Sala class:

class Sala {
  String note;
  String noteDes;
  Sala({this.note, this.noteDes});
}

When I try to run it, I get this:

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): ════════════════════════════════════════════════════════════════════════════════════════════════════

If you can help, I will really appreciate it! If you have any questions, please let me know in the comments!

Your code has bad formatting and this is not editable because as stackoverflow guidelines mentionned you should explain your problem, give examples and context which you didn't do. Please give us detail. — Jao

Nitesh Nitesh · Accepted Answer · 2021-02-17T10:15:21

You need to wrap your Scaffold with

MaterialApp()

because this is the widget that introduces MediaQuery

Changes in build of MyApp:

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: Scaffold(
       ...
      ),
    );

Exception Caught By Widgets Library error in Flutter

2 Answers