Skin Button as Spinner to create custom (multiselect) spinner

I'm trying to create a spinner-like widget that can support single selection, multiselect and multiselect with an "othe开发者_如何学Gor, type it in" element. To do this I'm taking a Button and attaching a popup ListView (i.e. AlertDialog with listview) which will handle the selection. However I'd like to skin the button to look like a Spinner (with the pointing down arrow) so that to a user it seems like an advanced spinner without all the hassle of extending Spinner and reimplementing a load of stuff. The problem is I can't find the resource Android uses for the spinner, i've looked at the source code and found many drawables in Platform/Frameworks/Core/core/res but nothing that resembles what I want.

Does anyone have any ideas? Or am I better off extending Spinner instead?

Thanks! :)