How to run some codes before closing aspx that is opened by RadWindowManager-

[Kem Arda]

Just before closing aspx (that is opened using RadWindowManager) from X , I need to do some check outs in code behind of the same aspx( some sums and some bool controls). If all check outs are passed i wantto close the aspx from X, otherwise i wantto alert and not close the window.

How can i do that?