Hide Button on role center

Hello,

I'd like to hide a button on role center from code using visible proriety, so I declared a variable named "hideBt" with IncludeInDataset = yes.

I put hideBt in visible propriety of control to hide.

I tried to change a value to false in OnInit trigger and OnOpenPage tirgger but it doesn't work  !! 

How could I do it ?

Thank's for your help.