一、报错信息

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Flutter 应用运行时报如下错误 :

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 1
Performing 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=/ws
Syncing 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: Scaffolddirtystate: 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:5:10
When 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)
...
====================================================================================================

出错代码 :

void main() {runApp(HeroAnimation());
}class HeroAnimation extends StatelessWidget{@overrideWidget build(BuildContext context) {// 时间膨胀系数 , 用于降低动画运行速度timeDilation = 10.0;return Scaffold(appBar: AppBar(title: Text("Hero 动画演示( 跳转前页面 )"),),body: Center(child: HeroWidget(imageUrl: "https://img-blog.csdnimg.cn/20210329101628636.jpg",width: 300,),),);}
}

二、解决方案

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出现上述问题 , 是因为在界面的根组件 , 没有使用 MaterialApp 组件 , 在 main.dart 中的 main 函数中 , 运行的组件的根组件必须是 MaterialApp ;

在 Scaffold 组件的外层包裹一层 MaterialApp , 即可解决问题 ;

class HeroAnimation extends StatelessWidget{@overrideWidget build(BuildContext context) {// 时间膨胀系数 , 用于降低动画运行速度timeDilation = 10.0;return MaterialApp(home: Scaffold(appBar: AppBar(title: Text("Hero 动画演示( 跳转前页面 )"),),body: ,),);}}