AdMob Banner Ads of andorid

  implementation(group = "com.google.android.gms", name = "play-services-ads", version = "19.3.0")

 <?xml version="1.0" encoding="utf-8"?>
 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/main"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context=".MainActivity">

     <com.google.android.gms.ads.AdView
         android:id="@+id/adView"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_alignParentBottom="true"
         android:layout_centerHorizontal="true"
         app:adSize="BANNER"
         app:adUnitId="@string/admob_banner_id"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />

 </androidx.constraintlayout.widget.ConstraintLayout> 

 import android.annotation.SuppressLint
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
 import com.google.android.gms.ads.AdRequest
 import com.google.android.gms.ads.AdView
 import com.google.android.gms.ads.MobileAds


 class MainActivity : AppCompatActivity() {
     @SuppressLint("MissingInflatedId")
     lateinit var adView: AdView
     @SuppressLint("VisibleForTests")
     lateinit var adRequest: AdRequest
     @SuppressLint("VisibleForTests")
     override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
         //initialize Mobileads
          MobileAds.initialize(this)
         //create object
         adView = findViewById(R.id.adView)
         //adrequest builder
         adRequest = AdRequest.Builder().build()
         //load ads
         adView.loadAd(adRequest)
     }
 }