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Re: Help with dynamic functionality

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  • Subject: [mg128824] Re: Help with dynamic functionality
  • From: Fred Simons <f.h.simons at>
  • Date: Thu, 29 Nov 2012 06:03:06 -0500 (EST)
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A further simplication shows wat is going on and how to achieve what you 
are looking for:

Grid[{{Checkbox[Dynamic[y]], Dynamic[y]},
   {Dynamic[x], Slider[Dynamic[x, (x = If[y, #, 0]) &]]}}]

Check the checkbox and move the slider. Then uncheck the checkbox. That 
changes the value of y, so the updating mechanism starts. For updating 
the the slider, the frontend  asks the kernel to evaluate the first 
argument, that is in this case  x only, which as not changed. If you 
want that unchecking the box has an effect on the slider, the first 
argument of the slider must depend on the variable y as well, e.g.

{Checkbox[Dynamic[y]], Dynamic[y],
  Slider[Dynamic[If[y, x, 0], (x = #) &]], Dynamic[x]}

Observe that the last Dynamic[x] shows that even when the the checkbox 
is unchecked, assignments to x are done when the slider is used. To 
prevent that, instead of (x=#)& you can use If[y, x=#]&.

Fred Simons
Eindhoven University of Technology

Op 28-11-2012 9:17, samid.hoda at schreef:
> My actual problem is quite involved but I am including a simple example for
>   illustrative purposes. I am trying to reproduce "Enabled"-like functionality as follows:
> Clear[y, SliderModule];
> SetAttributes[SliderModule, HoldAll];
> SliderModule[enabled_] :=
>   DynamicModule[{x = 0}, {Slider[
>      Dynamic[x, (x = If[enabled, #, 0]) &]], Dynamic[x]}]
> {Checkbox[Dynamic[y]], Dynamic[y], SliderModule[y]}
> Ideally when the checkbox is checked then the user is able to move the slider; but when it is unchecked the slider resets to zero. The problem is when I uncheck the checkbox the slider doesn't reset to zero until I click on the slider itself. Is there a way to get the slider to immediately reset when I uncheck the checkbox? Please remember that this is a simplification of my actual problem so try to keep the SliderModule structure the same.
> Cheers,
> Sam
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