Spacing ImageButtons in Android

How do you space ImageButtons?

With RelativeLayout, I can have them side by side but I want a gap between them. How do I place the buttons in the center and at the 开发者_开发问答bottom of the screen?

With RelativeLayout, I can have them side by side but I want a gap between them.

Use android:layout_marginTop and related properties.

How do I place the buttons in the center and at the bottom of the screen?

android:layout_centerHorizontal="true" and android:layout_alignParentBottom="true"