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

On Feb 23, 2012, at 2:01 PM, Kieron Hardy wrote:

> Look like this will work very nicely indeed ... Thanks.
> 
> Am I correct in thinking that 'button-colors' models a 3-element ring buffer where 'cdr' advances the access window one element?

yes. 


> 
> On Thu, Feb 23, 2012 at 10:59 AM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> 
> Would this work for you:
> 
> #lang racket/gui
> 
> (define (make-colored-bm color:str)
>  [define bm (make-object bitmap% 200 200)]
>  [define dc (make-object bitmap-dc% bm)]
>  (send dc set-brush (make-object brush% color:str 'solid))
>  (send dc draw-rectangle 0 0 200 200)
>  (send dc set-bitmap #f)
>  bm)
> 
> (define frame (new frame% [label "test"] [width 200] [height 200]))
> 
> (define panel (new panel% [parent frame]))
> 
> (define button-colors
>  (shared ([c (append (map make-colored-bm '("green" "red" "blue")) c)])
>    c))
> 
> (define buttn
>  (new button%
>       [label (car button-colors)]
>       [parent panel]
>       [callback (lambda (b e)
>                   (set! button-colors (cdr button-colors))
>                   (send buttn set-label (car button-colors)))]))
> 
> (send frame show #t)
> 
>