main.xml

<com.google.ads.AdView android:id="@+id/adView"
                               android:layout_width="wrap_content"
                               android:layout_height="wrap_content"
                               android:gravity="center"
                               ads:adUnitId="@string/admob_publisher_id"
                               ads:adSize="BANNER"
                               ads:loadAdOnCreate="false"
                               android:layout_alignParentRight="true"
                               android:layout_alignParentBottom="true"/>