Catch click event in BSP-page (web interface)

Hi Folks!

In my Web Interface, I have created a planning function button of type user-exit. The function does a file upload. When the user clicks on the button I need to do a few checks in ABAP (before the actual function executes). Question is... where exactly can I catch the click-event and do these checks?

I tried a few things with the generated bsp-app in se80, but nothing seemed to catch the click event.

Thanks a lot in advance for your input!

Simon