Relative layout trick

gistfile1.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        
    <RelativeLayout android:id="@+id/map_container"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent">
    </RelativeLayout>

    <Button android:id="@+id/current_location_center"
               android:layout_width="50dp"
               android:layout_height="0dp"
               android:layout_centerInParent="true"
               android:visibility="invisible"
               android:contentDescription="My location dummy"/>


    <ImageView android:id="@+id/current_location"
               android:layout_width="40dp"
               android:layout_height="40dp"
               android:src="@drawable/marker_pin"
               android:layout_centerHorizontal="true"
               android:layout_alignBottom="@id/current_location_center"

               android:contentDescription="My location"/>
</RelativeLayout>