React Native java.lang.ClassNotFoundException：找不到类

Question

The app crashes on device on start, this is the log:

Note I replaced my original 'com.appname' with com.myappName

07-20 13:10:05.520  5376  5376 E AndroidRuntime: FATAL EXCEPTION: main
07-20 13:10:05.520  5376  5376 E AndroidRuntime: Process: com.myappName, PID: 5376
07-20 13:10:05.520  5376  5376 E AndroidRuntime: java.lang.RuntimeException: Unable to instantiate application com.myappName.MainApplication package com.myappName: java.lang.ClassNotFoundException: Didn't find class "com.myappName.MainApplication" on path: DexPathList[[zip file "/data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/base.apk"],nativeLibraryDirectories=[/data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/lib/x86_64, /data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/base.apk!/lib/x86_64, /system/lib64, /system_ext/lib64]]
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.LoadedApk.makeApplicationInner(LoadedApk.java:1463)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.LoadedApk.makeApplicationInner(LoadedApk.java:1392)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6740)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.ActivityThread.-$$Nest$mhandleBindApplication(Unknown Source:0)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2132)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.os.Handler.dispatchMessage(Handler.java:106)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.os.Looper.loopOnce(Looper.java:201)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.os.Looper.loop(Looper.java:288)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.ActivityThread.main(ActivityThread.java:7892)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at java.lang.reflect.Method.invoke(Native Method)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)
07-20 13:10:05.520  5376  5376 E AndroidRuntime: Caused by: java.lang.ClassNotFoundException: Didn't find class "com.myappName.MainApplication" on path: DexPathList[[zip file "/data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/base.apk"],nativeLibraryDirectories=[/data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/lib/x86_64, /data/app/~~jMKAsYSvEjMZSEi2dXirHg==/com.myappName-u02x8yQYisyfG6ITJEv3UA==/base.apk!/lib/x86_64, /system/lib64, /system_ext/lib64]]
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.AppComponentFactory.instantiateApplication(AppComponentFactory.java:76)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at androidx.core.app.CoreComponentFactory.instantiateApplication(CoreComponentFactory.java:52)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.Instrumentation.newApplication(Instrumentation.java:1232)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    at android.app.LoadedApk.makeApplicationInner(LoadedApk.java:1455)
07-20 13:10:05.520  5376  5376 E AndroidRuntime:    ... 11 more

It used to work fine before both on Mac and here on Linux. After installing fresh Linux distro and cloning the git repository, this started happening

Here is what I did:

1. Cloned git repository
2. npm install --save-exact
3. React Native enviroment / Android is set up properly - no errors regarding that

android/app/build.gradle

    defaultConfig {
        applicationId "com.myappName"
        minSdkVersion rootProject.ext.minSdkVersion
        targetSdkVersion rootProject.ext.targetSdkVersion
        versionCode 20
        versionName "2.0"
    }

/android/app/src/main/AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.myappName">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
      android:name=".MainApplication"
      android:label="@string/app_name"
      android:icon="@mipmap/ic_launcher"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:allowBackup="false"
      android:theme="@style/AppTheme">
      <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:configChanges="keyboard|keyboardHidden|orientation|screenSize|uiMode"
        android:launchMode="singleTask"
        android:windowSoftInputMode="adjustResize">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
      </activity>
    </application>
</manifest>

Emulator is Resizeable API 33 x86_64

Thanks

Answer 1

检查您的 MainActivity.java 和 MainApplication.java 文件的第一行，它应该是com.myappName

Answer 2

I was missing Java files. Fixed the issue by rebuilding android and ios folders with react-native-eject

npm install react-native-eject
sudo rm -rf android ios
npx react-native eject

Make sure to replace package name manually in .java files afterwards.