[error record] an error is reported in the fluent interface (no mediaquery widget ancestor found. | scaffold widgets require a mediaquery)

One 、 Error message

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Flutter The application runs with the following errors :

Launching lib\main.dart on Pixel 2 in debug mode...Running Gradle task 'assembleDebug'...√ Built build\app\outputs\flutter-apk\app-debug.apk.Installing build\app\outputs\flutter-apk\app.apk...Uninstalling old version...Error: ADB exited with exit code 1Performing Streamed Installadb: failed to install D:\002_Project\002_Android_Learn\flutter_animation\build\app\outputs\flutter-apk\app.apk: Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package kim.hsl.flutter_animation signatures do not match previously installed version; ignoring!]Installing build\app\outputs\flutter-apk\app.apk...Debug service listening on ws://127.0.0.1:59548/20KwYgDmkUc=/wsSyncing files to device Pixel 2...======== Exception caught by widgets library =======================================================The following assertion was thrown building HeroAnimation:No MediaQuery widget ancestor found.Scaffold widgets require a MediaQuery widget ancestor.The specific widget that could not find a MediaQuery ancestor was: Scaffold  dirty  state: ScaffoldState#6ef6f(lifecycle state: initialized, tickers: tracking 2 tickers)The ownership chain for the affected widget is: "Scaffold ← HeroAnimation ← [root]"No MediaQuery ancestor could be found starting from the context that was passed to MediaQuery.of(). This can happen because you have not added a WidgetsApp, CupertinoApp, or MaterialApp widget (those widgets introduce a MediaQuery), or it can happen if the context you use comes from a widget above those widgets.The relevant error-causing widget was:   HeroAnimation file:///D:/002_Project/002_Android_Learn/flutter_animation/lib/main.dart:5:10When the exception was thrown, this was the stack: #0      debugCheckHasMediaQuery.<anonymous closure> (package:flutter/src/widgets/debug.dart:219:7)#1      debugCheckHasMediaQuery (package:flutter/src/widgets/debug.dart:234:4)#2      MediaQuery.of (package:flutter/src/widgets/media_query.dart:820:12)#3      ScaffoldState.didChangeDependencies (package:flutter/src/material/scaffold.dart:2820:50)#4      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4725:11)...====================================================================================================

Error code :

void main() { 
      runApp(HeroAnimation());}class HeroAnimation extends StatelessWidget{ 
      @override  Widget build(BuildContext context) { 
        //  Time expansion coefficient  ,  Used to reduce the running speed of animation     timeDilation = 10.0;    return Scaffold(      appBar: AppBar(        title: Text("Hero  The demo (  Jump to the front page  )"),      ),      body: Center(        child: HeroWidget(          imageUrl: "https://img-blog.csdnimg.cn/20210329101628636.jpg",          width: 300,        ),      ),    );  }}

Two 、 Solution

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The above problems occur , Because the root component in the interface , Not used MaterialApp Components , stay main.dart Medium main Function , The root component of the running component must be MaterialApp ;

stay Scaffold The outer layer of the component is wrapped with a layer MaterialApp , Problem solvable ;

class HeroAnimation extends StatelessWidget{ 
      @override  Widget build(BuildContext context) { 
        //  Time expansion coefficient  ,  Used to reduce the running speed of animation     timeDilation = 10.0;    return MaterialApp(      home: Scaffold(        appBar: AppBar(          title: Text("Hero  The demo (  Jump to the front page  )"),        ),        body: ,      ),    );  }}