我在 Android 中面临 ClassNotFoundException

Question

I'm trying to create a Chat app that uses Firebase. But suddenly I'm facing this error.

02-13 10:23:02.533446   733   733 E AndroidRuntime: FATAL EXCEPTION: main
02-13 10:23:02.533446   733   733 E AndroidRuntime: Process: com.mycompany.myapp3, PID: 733
02-13 10:23:02.533446   733   733 E AndroidRuntime: java.lang.RuntimeException: Unable to instantiate application com.mycompany.myapp3.MyApplication: java.lang.ClassNotFoundException: Didn't find class "com.mycompany.myapp3.MyApplication" on path: DexPathList[[zip file "/data/app/com.mycompany.myapp3-1/base.apk"],nativeLibraryDirectories=[/data/app/com.mycompany.myapp3-1/lib/arm, /system/lib, /vendor/lib, /system/vendor/lib]]
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.LoadedApk.makeApplication(LoadedApk.java:807)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5477)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.ActivityThread.-wrap2(ActivityThread.java)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1595)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:110)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.os.Looper.loop(Looper.java:203)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:6251)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
02-13 10:23:02.533446   733   733 E AndroidRuntime: Caused by: java.lang.ClassNotFoundException: Didn't find class "com.mycompany.myapp3.MyApplication" on path: DexPathList[[zip file "/data/app/com.mycompany.myapp3-1/base.apk"],nativeLibraryDirectories=[/data/app/com.mycompany.myapp3-1/lib/arm, /system/lib, /vendor/lib, /system/vendor/lib]]
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at java.lang.ClassLoader.loadClass(ClassLoader.java:380)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.Instrumentation.newApplication(Instrumentation.java:992)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     at android.app.LoadedApk.makeApplication(LoadedApk.java:801)
02-13 10:23:02.533446   733   733 E AndroidRuntime:     ... 9 more

build.gradle:

apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'

android {
    compileSdkVersion 27
    defaultConfig {
        applicationId "com.mycompany.myapp3"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    buildTypes {
        debugg {
            debuggable true
        }
    }
}

dependencies {
    implementation 'com.google.android.gms:play-services-analytics:15+'
    implementation 'com.google.firebase:firebase-storage:15+'
    implementation 'de.hdodenhof:circleimageview:3.1.0'
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support:recyclerview-v7:27.1.1'
    implementation 'com.google.firebase:firebase-auth:15+'
    implementation 'com.google.firebase:firebase-database:15+'
}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mycompany.myapp3" >
    
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
        
    <application
        
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme" >
        <activity android:name=".StartActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".RegisterActivity" />
        <activity
            android:name=".ResetPasswordActivity" />
        <activity
            android:name=".LoginActivity" />
        <activity
            android:name=".MainActivity" />
        <activity
            android:name="ChatActivity" />
        <activity
            android:name=".UserProfileActivity" />
        <!--<activity
            android:name=".ImageActivity" />-->
        <activity
            android:name=".DebugActivity"
            android:screenOrientation="portrait"/>
        <meta-data
            android:name="android.max_aspect"
            android:value="4.0"/>
        
        <uses-library android:name="org.apache.http.legacy" android:required="false" />
    </application>

</manifest>

I don't know how Do I fix it. I will apprentice if you can help.

NOTE: Please, I'm a beginner in this feild. I really need help. If I missed to share any information, please let me know, I'll add the information.

Thanks.

Answer 1

It looks like You have not registered your Application class in AndroidManifest file.

Register like this

<application
android:name=".MyApplication">

Answer 2

For android studio 4+, you need to enable Java 8 like this in your build.gradle (app) :

android {
    defaultConfig {
            ...
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}