[racket] Changing the background color of a GUI button.

The idea of `set-state-normal' and `set-state-selected' sounds like a
`check-box%' rather than a `button%'.

Otherwise, there's no way to change the background color of a `button%'
instance. Classes like `button%' correspond to platform-specific GUI
widgets that typically either don't support or strongly discourage the
possibility of changing a button's background (because button colors
are normally determined by a theme). You can create a `canvas%' that
draws a custom button image, in which case you have complete control
over how the button looks and reacts, but there isn't much of an
in-between level of customization in the current toolkit.

At Tue, 21 Feb 2012 00:25:52 -0700, Kieron Hardy wrote:
> Hi all,
> 
> How do I change the background color (and/or style of border etc.) of a GUI
> button? Given the code below, what should I put in the set-state-x methods
> to indicate a difference between a normal and selected button?
> 
> Also any comments on program style and/or substance are appreciated (I
> apologize in advance if the layout offends).
> 
> Cheers,
> 
> Kieron.
> 
> ****
> 
> #lang racket/gui
> 
> (define color-button%
>   (class button%
>     (inherit refresh)
> 
>     (define toggle
>       (let ([f #f])
>         (lambda ()
>           (set! f (not f))
>           f
>           )
>         )
>       )
> 
>     (define (set-state-normal)
>       (printf "color-button%: set-state-normal:\n")
>       ; ??? ; set background color to normal
>       (refresh)
>       )
> 
>     (define (set-state-selected)
>       (printf "color-button%: set-state-selected:\n")
>       ; ??? ; set background color to red
>       (refresh)
>       )
> 
>     (define click-callback
>       (lambda (button control-event)
>         (printf "color-button%: click-callback:\n")
>         (if (toggle)
>           (set-state-selected)
>           (set-state-normal)
>           )
>         )
>       )
> 
>     (super-new (callback click-callback))
> 
>     )
>   )
> 
> (define f (new frame%
>                [label "Colored Button"]
>                [min-width 100]
>                [min-height 200]
>                )
>   )
> 
> (define b (new color-button%
>               [parent f]
>               [label "push me"]
>               )
>   )
> 
> (send f show #t)
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