无法实例化应用程序并且找不到类

Question

这是我在终端中运行flutter run 时的主要问题

Launching lib\main.dart on TECNO LB7 in debug mode...
Running Gradle task 'assembleDebug'...                                  

Running Gradle task 'assembleDebug'... Done                       178.4s (!)
√ Built build\app\outputs\flutter-apk\app-debug.apk.
Installing build\app\outputs\flutter-apk\app.apk...                31.1s
E/AndroidRuntime(17767): FATAL EXCEPTION: main
E/AndroidRuntime(17767): Process: com.example.firebasepractice, PID: 17767
E/AndroidRuntime(17767): java.lang.RuntimeException: Unable to instantiate application com.example.firebasepractice: java.lang.ClassNotFoundException: Didn't find class "com.example.firebasepractice" on path: DexPathList[[zip file "/data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/lib/arm, /data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/base.apk!/lib/armeabi-v7a, /system/lib, 
/vendor/lib]]
E/AndroidRuntime(17767):        at android.app.LoadedApk.makeApplication(LoadedApk.java:999)
E/AndroidRuntime(17767):        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5757)
E/AndroidRuntime(17767):        at android.app.ActivityThread.-wrap1(Unknown Source:0)
E/AndroidRuntime(17767):        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1691)
E/AndroidRuntime(17767):        at android.os.Handler.dispatchMessage(Handler.java:106)
E/AndroidRuntime(17767):        at android.os.Looper.loop(Looper.java:164)
E/AndroidRuntime(17767):        at android.app.ActivityThread.main(ActivityThread.java:6549)
E/AndroidRuntime(17767):        at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(17767):        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
E/AndroidRuntime(17767):        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:888)       
E/AndroidRuntime(17767): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.firebasepractice" on path: DexPathList[[zip file "/data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/lib/arm, /data/app/com.example.firebasepractice-LyPE1lNorhYSOJyU9fBj_Q==/base.apk!/lib/armeabi-v7a, /system/lib, /vendor/lib]]
E/AndroidRuntime(17767):        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
E/AndroidRuntime(17767):        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
E/AndroidRuntime(17767):        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
E/AndroidRuntime(17767):        at android.app.Instrumentation.newApplication(Instrumentation.java:1087)
E/AndroidRuntime(17767):        at android.app.LoadedApk.makeApplication(LoadedApk.java:993)
E/AndroidRuntime(17767):        ... 9 more

当我运行flutter doctor 时，它给了我这个：

[√] Flutter (Channel beta, 1.20.2, on Microsoft Windows [Version 10.0.18362.418], locale en-US)
    • Flutter version 1.20.2 at C:\flutter
    • Framework revision bbfbf1770c (3 weeks ago), 2020-08-13 08:33:09 -0700
    • Engine revision 9d5b21729f
    • Dart version 2.9.1

 
[√] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at C:\Users\FutureAlex\AppData\Local\Android\sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 48.1.2
    • Dart plugin version 193.7361
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code, 64-bit edition (version 1.48.1)
    • VS Code at C:\Program Files\Microsoft VS Code
    • Flutter extension version 3.13.2

[√] Connected device (3 available)
    • TECNO LB7 (mobile) • 043803395H000877 • android-arm    • Android 8.1.0 (API 27)
    • Web Server (web)   • web-server       • web-javascript • Flutter Tools
    • Chrome (web)       • chrome           • web-javascript • Google Chrome 84.0.4147.135

• No issues found!

Answer 1

您是否更改了您的包裹名称？它似乎在寻找不同的路径

Answer 2

/我通过在项目路径中添加 Application.kt 文件解决了我的错误，例如：“project_name\android\app\src\main\kotlin\com\example\firebasepractice\Application.kt”

    package com.example.project_name;

    import io.flutter.app.FlutterApplication;
    import io.flutter.plugin.common.PluginRegistry;
    import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback;
    import io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService;

    class Application : FlutterApplication(), PluginRegistrantCallback {
        override fun onCreate() {
            super.onCreate()
    FlutterFirebaseMessagingService.setPluginRegistrant(this);
}

    override fun registerWith(registry: PluginRegistry?) {
       registry?.registrarFor("io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin");
}

}