文章目录
一、报错信息
二、解决方案
一、报错信息
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 Install adb: 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: 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:5:10 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{ @override Widget 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
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{ @override Widget 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: , ), ); } }