Ah, that at least explains the motivation.
Well, see what Excel does? It puts a dropdown arrow button within the header caption. So indeed every header at first glance looks like a combobox. But it isn't really a combobox. The dropdown simply is something like a form or container. You could do the latter in VFP, too. So don't use a combobox, just add a button there and let that show a container "dropping down" (you don't have to animate it, rather set it visible =.t. or create it at that moment). Then use a multiselect listbox in that container and two buttons OK and Cancel.
It's up to you what you show when the user closes that container with OK or Cancel. Maybe just change a button caption from "pick categories" to "picked categories" to indicate the column is actively filtering data and back to "pick categories" when no category is picked and data isn't filtered by that column filter control. A normal combobox - even if it had multi-select - would still not be able to show all picks in the one row in the collapsed state.
As your layout already differs from Excels idea to have that within the header make the best of that, you're free to do whatever you want. In case of a textbox for entering a filter value, it is even simpler to use as Excels way, but in this case, I'd just use a button. Maybe a textbox plus a button, and then an extra container, or even a form you position there, set without titlebar. Whatever, but you are not the owner of the dropdown portion of a combobox, so use something else.
Bye, Olaf.
Olaf Doschke Software Engineering