I dont know enough about this stuff, other than to 'rather slavishly' follow
your code and make it work. :O)
Try this:
...
(define/override (on-paint) ; eliminate the argument
(define dc (send this get-dc)) ; 'this' is the current instance
...
On Aug 23, 2012, at 6:29 PM, Gregory Woodhouse wrote:
> I apologize in advance for the elementary nature of this question, and for
> the amount of code included below. I'm having a tough time following the
> documentation for racket/gui and racket/draw. My first attempt to create a
> Sudoku grid follows the example in the documentation rather slavishly and
> works fine
>
>
> (define frame (new frame% [label "Sudoku"]
> [width 300]
> [height 300]))
>
> (define grid-canvas (new canvas% [parent frame]
> [min-width 300]
> [min-height 300]
> [paint-callback
> (lambda (canvas dc)
> (let
> ([w (send canvas get-width)]
> [h (send canvas get-height)])
> (send dc set-pen "black" 3 'solid)
> (for ([i (in-range 3)])
> (send dc draw-line 0 (* i (/ h 3)) w (* i (/ h 3)))
> (send dc draw-line (* i (/ w 3)) 0 (* i (/ w 3)) h))
> (send dc set-pen "black" 1 'solid)
> (for ([i (in-range 9)])
> (send dc draw-line 0 (* i (/ h 9)) w (* i (/ h 9))))
> (for ([i (in-range 9)])
> (send dc draw-line (* i (/ w 9)) 0 (* i (/ w 9))
> h))))]))
>
> ; Show the frame by calling its show method
> (send frame show #t)
>
>
> But this does not work
>
> (define frame (new frame% [label "Sudoku"]
> [width 300]
> [height 300]))
>
> (define grid-canvas%
> (class canvas%
> (define/override (on-paint dc)
> (let
> ([w (send this get-width)]
> [h (send this get-height)])
> (send dc set-pen "black" 3 'solid)
> (for ([i (in-range 3)])
> (send dc draw-line 0 (* i (/ h 3)) w (* i (/ h 3)))
> (send dc draw-line (* i (/ w 3)) 0 (* i (/ w 3)) h))
> (send dc set-pen "black" 1 'solid)
> (for ([i (in-range 9)])
> (send dc draw-line 0 (* i (/ h 9)) w (* i (/ h 9))))
> (for ([i (in-range 9)])
> (send dc draw-line (* i (/ w 9)) 0 (* i (/ w 9)) h))))
> (super-new)))
>
> (define the-grid (new grid-canvas% [parent frame]
> [min-width 300]
> [min-height 300]))
>
>
> I get an arity mismatch in on-paint.
>
> The reason for not wanting in to pass in the paint-callback is that I want to
> be able to augment it somewhat in grid-canvas% (specifically, I need to draw
> in the digits based on the contents of the grid!) It's not clear (to me) how
> to do this, or if I should be taking an entirely different approach.
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