MediaQuery.of throws an exception inside MaterialApp-CodePudding

I'm newbie in Flutter.
I have very simple app

main.dart:

import 'package:dart_test/views/widgets/items/pack_items.dart';
import 'package:dart_test/views/widgets/items/pack_row.dart';
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print("app build");
    var pdata =
        PackData(packId: 'npack1', name: 'Pack1', name_ru: 'пак 1', nImages: 5);
    //print("~w:$contW");
    return MaterialApp(
        home: PackBody(data: pdata, offset: 0).build(context));
  }
}

PackBody.dart:

class PackBody extends ListItem {
  final PackData data;
  final int offset;
  PackBody({required this.data, required this.offset});

  @override
  Widget build(BuildContext context) {
    var ar = 896.0 / 768;
    //var contWidth=MediaQuery.of(context).size.width;
    return Container(
      width: MediaQuery.of(context).size.width,
      height: 50,
      child: Text('khkljgkjhgkjhg'),
    );
  }
}

And it throws an exception: I tried to wrap PackBody with MediaQuery - no luck
Shouldn't MaterialApp provide MediaQuery down to the hierarchy?

CodePudding user response：

What you are doing is the same as writing:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print("app build");
    var pdata = PackData(packId: 'npack1', name: 'Pack1', name_ru: 'пак 1', nImages: 5);
    //print("~w:$contW");
    return MaterialApp(
      home: Container(
        width: MediaQuery.of(context).size.width,
        height: 50,
        child: Text('khkljgkjhgkjhg'),
      ),
    );
  }
}

The MediaQuery widget establishes a subtree in which media queries resolve to the given data. MaterialApp introduces a MediaQuery and keeps it up to date with the current screen metrics as they change. In order for MediaQuery.of(context) to work it needs to be in that subtree, and from the previous code sample I provided it clearly is not.