hi all<div dir="ltr">I am beginning in scheme language: I don't understant this: ;------------------------------------------------------------------------------------ #lang scheme/gui (define f (new frame% (label "test") )) (define c (new canvas% (parent f) (min-width 200) (paint-callback (ë (canvas dc) (send dc clear))))) (define dc (send c get-dc)) (send dc set-background (make-object color% "red")) (send dc draw-rectangle 0 0 50 50) (send f show #t ) ;--------------------------------------------------------------------------------------- Why set-background work : I see my canvas red; but draw-rectangle doesn't work there are no rectangle in my canvas. I try to delete set-background line but I don't see my rectangle. so I know if I put (send dc draw-rectangle 0 0 50 50) in paint-callback it will work . But i want draw a rectangle not directly in my canvas class. Thanks. </div>