how to catch a checkbox event

Hello:

i would like to ask one favor i am trying to catch a checkbox event from the alv , so the question is , how can i do that ?

this the segment of code that i am using

ls_fcat-fieldname = 'CHECK'.

ls_fcat-inttype = 'C'.

ls_fcat-outputlen = '1'.

ls_fcat-coltext = 'Checkbox'.

ls_fcat-seltext = 'Checkbox'.

ls_fcat-checkbox = 'X'.

ls_fcat-edit = 'X'.

ls_fcat-auto_value = 'X'.

append ls_fcat to itfieldcat.

clear ls_fcat.

when the user give a click at the checkbox how can i save this event?