Centering an ImageButton and a TextView in a RelativeLayout

android:layout_gravity="center" doesn't seem to work the same in a RelativeLayout as it does in a LinearLayout.

I would like both an ImageButton and a TextView to be centered in a RelativeLayout - is there a basic xml code for 开发者_开发知识库this?

android:layout_centerHorizontal="true"

Also :

android:layout_centerInParent 
android:layout_centerVertical