I am developing library and using that library as aar to my app as below sample project.

Library Project:

public class UserDevice {     private static final String TAG = "UserDevice";     private static Context mContext;     public UserDevice(final Context context) {         mContext = context.getApplicationContext();     }     private static String getAdvertisementId(Context context) {         String _myads = null;         try {             String id = com.google.android.gms.ads.identifier.AdvertisingIdClient.getAdvertisingIdInfo(context).getId();             if (id != null) {                 _myads = id;             }         } catch (Exception e) {             Log.e(TAG, "Could not get det ID.", e);         }         return _myads;     } } //build.gradle android {     compileSdkVersion 29     buildToolsVersion "29.0.3"     defaultConfig {         minSdkVersion 16         targetSdkVersion 29         versionCode 1         versionName "1.0"         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"         consumerProguardFiles 'consumer-rules.pro'     } ... } dependencies {     // default dependencies     // ...     implementation 'com.google.android.gms:play-services-base:17.2.1'     implementation 'com.google.android.gms:play-services-ads:19.0.1' } 

App Project:

class MainActivity : AppCompatActivity() {     override fun onCreate(savedInstanceState: Bundle?) {         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)         val device = UserDevice(this) //         btn_show_ads.setOnClickListener {             label_ads_id.text = device.myads             Log.d("App", "Device Ads id is: ${device.myads}")         }     } } /// build.gradle dependencies {     // default dependencies     // ...     compile(name: 'adslibrary', ext: 'aar')     // compile project(path: ':adslibrary') } 

But what happened here is that it giving error

2020-05-11 10:11:32.489 21925-21991/com.bhavdip.myadstest E/AndroidRuntime: FATAL EXCEPTION: Thread-2     Process: com.bhavdip.myadstest, PID: 21925     java.lang.NoClassDefFoundError: Failed resolution of: Lcom/google/android/gms/ads/identifier/AdvertisingIdClient;         at com.bhavdip.adslibrary.CRDevice.getAdvertisementId(Unknown Source:2)         at com.bhavdip.adslibrary.CRDevice$1.run(Unknown Source:4)         at java.lang.Thread.run(Thread.java:764)      Caused by: java.lang.ClassNotFoundException: Didn't find class "com.google.android.gms.ads.identifier.AdvertisingIdClient" on path: DexPathList[[zip file "/data/app/com.bhavdip.myadstest-fP-f0WbH8_ErVLG3QBcgkQ==/base.apk"],nativeLibraryDirectories=[/data/app/com.bhavdip.myadstest-fP-f0WbH8_ErVLG3QBcgkQ==/lib/arm, /system/lib, /vendor/lib]]         at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:134)         at java.lang.ClassLoader.loadClass(ClassLoader.java:379)

I already added and am using gms:play-services-ads dependency in library. The app again asks me to add those dependency forcefully.

If I will add the dependency to the app it works fine, but I don't want to add that dependency again. I don't want to expose my library dependency to end user or developer. Adds below dependency to my-library.

//For advertisement ID implementation 'com.google.android.gms:play-services-ads:19.1.0' implementation 'com.google.android.gms:play-services-base:17.2.1' 

Reference links: I tried this and this too. I also checked all answers in reference links.

I have tried multidex, transitive and also changed implementation to api or compile. in app project like this.

// Use transitive compile(name: 'adslibrary', ext: 'aar') {     transitive = true } 

----- EDIT for Questions -----

• What is transitive? How it works?
• How multidex works in library?

I might miss something to change. Please help me out of this problem.