用于 MainActivity 的 Android API 26 上的 ClassNotFoundException（使用 API 30）答案

【问题标题】：ClassNotFoundException on Android API 26 for MainActivity (working with API 30)用于 MainActivity 的 Android API 26 上的 ClassNotFoundException（使用 API 30）
【发布时间】：2020-07-13 15:45:02
【问题描述】：

我有一个 Android Studio 项目，我在 API 30 上进行了测试，并且运行良好。现在我尝试在 API 26（这是我为项目设置的最低 SDK 版本）上运行它，但我无法启动应用程序。两次我都使用了模拟的 Pixel 3a 和一个外部设备。

错误日志：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.main.xyz, PID: 9389
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.main.xyz/com.main.xyz.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.main.xyz.MainActivity" on path: DexPathList[[zip file "/data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/lib/x86, /system/lib, /vendor/lib]]
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2718)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
    at android.app.ActivityThread.-wrap11(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
 Caused by: java.lang.ClassNotFoundException: Didn't find class "com.main.xyz.MainActivity" on path: DexPathList[[zip file "/data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/lib/x86, /system/lib, /vendor/lib]]
    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:93)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1173)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2708)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
    at android.app.ActivityThread.-wrap11(Unknown Source:0) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
    at android.os.Handler.dispatchMessage(Handler.java:105) 
    at android.os.Looper.loop(Looper.java:164) 
    at android.app.ActivityThread.main(ActivityThread.java:6541) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
    Suppressed: java.io.IOException: Failed to open dex files from /data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/base.apk because: Failure to verify dex file '/data/app/com.main.xyz-rZkYLBaLo3gdkb7oCChonQ==/base.apk': Bad method handle type 7
    at dalvik.system.DexFile.openDexFileNative(Native Method)
    at dalvik.system.DexFile.openDexFile(DexFile.java:353)
    at dalvik.system.DexFile.<init>(DexFile.java:100)
    at dalvik.system.DexFile.<init>(DexFile.java:74)
    at dalvik.system.DexPathList.loadDexFile(DexPathList.java:374)
    at dalvik.system.DexPathList.makeDexElements(DexPathList.java:337)
    at dalvik.system.DexPathList.<init>(DexPathList.java:157)
    at dalvik.system.BaseDexClassLoader.<init>(BaseDexClassLoader.java:65)
    at dalvik.system.PathClassLoader.<init>(PathClassLoader.java:64)
    at com.android.internal.os.PathClassLoaderFactory.createClassLoader(PathClassLoaderFactory.java:43)
    at android.app.ApplicationLoaders.getClassLoader(ApplicationLoaders.java:69)
    at android.app.ApplicationLoaders.getClassLoader(ApplicationLoaders.java:36)
    at android.app.LoadedApk.createOrUpdateClassLoaderLocked(LoadedApk.java:676)
    at android.app.LoadedApk.getClassLoader(LoadedApk.java:709)
    at android.app.LoadedApk.getResources(LoadedApk.java:936)
    at android.app.ContextImpl.createAppContext(ContextImpl.java:2242)
    at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5672)
    at android.app.ActivityThread.-wrap1(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1661)
            ... 6 more

我的 MainActivity.java：

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
}
//Called by Button
public void login(View v) {
    Intent intent = new Intent(MainActivity.this, Uebersicht.class);
    startActivity(intent)
}

我的 build.gradle（应用程序）：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.0"

    defaultConfig {
        applicationId "com.main.xyz"
        minSdkVersion 26
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        proguardFiles 'proguard-rules.pro'
    }

    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.android.material:material:1.1.0'
    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
    implementation 'com.google.android.gms:play-services-vision:20.1.0'

}

我的 build.grade（项目）：

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:4.0.0"

    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

还有我的 manifest.xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.main.xyz">

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

    <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"
        android:usesCleartextTraffic="true">

        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Uebersicht"
            android:label="" />
        <activity
            android:name=".ProductActivity"
            android:label="" />
        <activity
            android:name=".AddActivity"
            android:label=""/>
        <activity
            android:name=".ScanActivity"
            android:label="" />
    </application>

</manifest>

我一直在寻找解决方案已经有一段时间了。由于我对 Android 还很陌生，因此我们非常感谢所有帮助。如果你能提供它，我真的很想解释我的问题以及能够理解这里出了什么问题的解决方案。

【问题讨论】：

给你看proguard。因为minifyEnabled true
proguard 都被注释掉了。 minifyEnabled true 只是我尝试过的一次，不会改变它是否有效
然后设置minifyEnabled false
好的，谢谢（但仍然无法启动）
干净-重建-运行。如果出现不同的错误日志，则通知

标签： java android classnotfoundexception android-8.0-oreo android-10.0

【解决方案1】：

我猜是 dexing 的问题，所以尝试在你的依赖项 gradle 中添加这个库，如下所示：

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.android.material:material:1.1.0'
    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
    implementation 'com.google.android.gms:play-services-vision:20.1.0'
    implementation 'com.android.support:multidex:1.0.3' // add this library 
}

并在此处添加此代码

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.0"

    defaultConfig {
        applicationId "com.main.xyz"
        minSdkVersion 26
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        proguardFiles 'proguard-rules.pro'
        multiDexEnabled true // add this line of code 
    }

【讨论】：

感谢您的回复，遗憾的是没有帮助.. 错误消息也保持不变
在您的 logcat 错误中，您可以单击错误并查看它会将您带到哪一行？

【解决方案2】：

我查看了 dexing 错误描述并找到了another question regarding java 8 support。实施

compileOptions {
        coreLibraryDesugaringEnabled true
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

和

coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:1.0.9'

进入应用的 build.gradle 文件解决了这个问题。

More information here

【讨论】：