The first step toward displaying a banner is to place AdView in the layout for the Activity or Fragment in which you'd like to display it. The easiest way to do this is to add one to the corresponding XML layout file. Here's an example that shows AdView at the bottom of an Activity:

main_activity.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        android:paddingBottom="@dimen/activity_vertical_margin"
        tools:context=".MainActivity">

        <TextView android:text="@string/hello_world"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <com.google.android.gms.ads.AdView
            xmlns:ads="http://schemas.android.com/apk/res-auto"
            android:id="@+id/adView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_alignParentBottom="true"
            ads:adSize="BANNER"
            ads:adUnitId="ca-app-pub-3940256099942544/6300978111">
        </com.google.android.gms.ads.AdView>

</RelativeLayout>

Note the following required attributes:

• ads:adSize - Set this to the ad size you'd like to use (see the banner size section below for details).
• ads:adUnitId - Set this to the unique identifier given to the ad unit in your app where ads are to be displayed. If you show banner ads in different activities, each would require an ad unit.