How to lay out 3 buttons above 4 buttons, centered?

I need to lay out a centered row of 3 buttons above a centered row of 4 buttons:

          +------+    +------+    +------+
          |      |    |      |    |      |
          +------+    +------+    +------+

    +------+    +------+    +------+    +------+
    |      |    |      |    |      |    |      |
    +------+    +------+ 开发者_如何学C   +------+    +------+

All the buttons are the same size and the inter-button gaps should be the same on both rows. I can do this easily with nested LinearLayouts, but I'd like to do this without nesting layout views. (Aside from all the advice to avoid nested layouts, I need to traverse the buttons in code and it's a lot easier with a flat layout.)

I can do this with a RelativeLayout if the rows have the same number of buttons, but I can't figure it out when the button counts differ. Is there a way to use one of the stock layout views (it seems silly to write a custom layout view for this) to do a flat layout?

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It seems like this can't be done in single layout. You can't use relative layout because it doesn't support gravity and you need views center aligned.

Custom layout is a perfect solution for this case. It's not that hard really. I experienced a lot simpler cases that couldn't be done using single standard layout.