@Thomas
Hey, thanks a bunch. But I'm finding that method not very practical. GA_ID only uses 2 bytes of size meaning I can't put my datatype handle in there directly. So I'd have to wonder through the window's gadget list till I find a particular ID... Even then I'd still have to get the datatype handle from the gadget structure...
I thought about using GA_UserData but it doesn't show up in the IDCMPUPDATE message....
Of course, I could dynamically build my own list of datatypes with their IDs, I just thought there was a more practical way to do it...
Cheers
José