Get parameter of form

Sorry this is about my poor english:

I created table “a_table”

I created a form for it “a_table_form”

I created a menu item “a_table_form_menu” for “a_table_form”

I referred “a_table_form_menu” to formref property of “a_table”

I want to know passed value at “a_table_form”'s init.

I can learn that value by get args.record() for a specific table, but “a_table_form” is calling from different tables, different field names so I don’t want to put a switch command for every table.