>Sorry about vague title.
>
>I have a grid. When the grid is built in code I want one of the columns to have checkbox class instead of textbox. So I remove the textbox and add a checkbox-based class:
>
>

>.RemoveObject( "Text1" )	
>.AddObject( "print_it", "chk_select_to_print" )
>

>
>The following is the code that defines the "chk_select_to_print" class:
>
>

>DEFINE CLASS chk_select_to_print AS CHECKBOX
>
> PROCEDURE InteractiveChange
>
>  if this.value
>     * my code goes here
>  else
>     * my code goes here
>  endif		
> END PROCEDURE
>		
>ENDDEFINE
>

You didn't forget to set column's sparse property to .f. and set this.column3.print_it.visible = .t., right?

And you're sure, that the checkbox has logical value (because it's often 1/0 rather than .t./.f.). Finally you may put your code into valid event.