An easy fix: Let the callback ignore calls, when the slider value
is the same as the last one.
Example:
(define substrate-slider
(let ([last-value-seen -42])
(make-slider pane
"[S]" 0 slider-max
(lambda (slider event)
(let ([n (send slider get-value)])
(unless (= n last-value-seen)
(set! last-value-seen n)
(set! s0 (exact->inexact (* smax (/ slider-max) n)))
(draw))))
(λ () s0)
(λ () smax))))
/Jens Axel
2012/4/1 Jens Axel Søgaard <[email protected]>:
> Hi All,
>
> I have a little problem with the attached program.
> Maybe, I am not 100% sure, the slider% calls the call-back
> more than once (maybe 4 times?) after the release of the mouse.
> The behaviour puzzles me.
>
> Is it the intended behaviour? If so, is there a better way
> to use the slider, than the one in the attached program?
>
> I found the following program by António Leitão from June 2011
> on the mailing list, which shows this oddity.
>
> (require racket/gui)
> (define frame (new frame% [label "Example"]))
> (new slider% [parent frame]
> [label "Test"]
> [min-value 0]
> [max-value 10]
> [callback (lambda (slider event)
> (display
> (format "~a@~a: ~a~%"
> (send event get-event-type)
> (send event get-time-stamp)
> (send slider get-value))))])
>
> (send frame show #t)
>
> On my computer, if I run the program, and then move the
> slider to 5 and release the mouse, I get this output:
>
> slider@-273484745: 0
> slider@-273484095: 1
> slider@-273482097: 5
> slider@-273482096: 5
> slider@-273482096: 5
> slider@-273482096: 5
> slider@-273482096: 5
--
Jens Axel Søgaard
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