Android Question Frame around Spinner

Dear All

I try to get a frame around some spinners, but it will not work. Here is what I am doing ....

...
Dim cd As ColorDrawable
cd.Initialize2(Colors.Transparent, 5dip, 2dip, Colors.Gray)
spiTag.Background=cd
spiMonat.Background=cd
spiJahr.Background=cd
edtAnzahlstarts.Background=cd
edtPilotIch.Background=cd
edtPilotBegleit.Background=cd
...

Here is the result:



You can nicely see that the frame is around the editboxes, but not around the three spinners at the top.

Whay is that?

Any help is highly appeciated.
Thanks and regards
René