1Let's have two buttons, @id/button1 and @id/button2.
2The constraint_referenced_ids field will reference them
3by simply having them as comma-separated list:
4
5<androidx.constraintlayout.widget.Barrier
6 android:id="@+id/barrier"
7 android:layout_width="wrap_content"
8 android:layout_height="wrap_content"
9 app:barrierDirection="bottom"
10 app:constraint_referenced_ids="button1,button2" />
11
12This way the barrier will allways be under button1 and button2.