How to validate data when press enter or save in maintenance view

Hi all,

     How to add some validation logic into maintenance view when user inputs some data in table control then press enter or click save ?

     I need to throw up an error message when data in one column duplicates, but I do not know where to add  custom code into the auto-generated code by table maintenance generator.

     I tried the event 01 and 05, in them I throw a message , however I do not see it, am I use it in the incorrect way?

     Thank you very much.

Best regards,

Xu Chris