Interaction between two sliders that update the same variable

Question

I'm basing this on the code found in the Introduction to Dynamics. I added one more slider which doesn't use the "round and snap" feature given in the link above:

DynamicModule[{x = 0},
 Column@{Slider[
    Dynamic[x, 
     If[Abs[# - Round[#]] < 0.3, x = Round[x], x = #] &], {0, 5}]
   , Slider[Dynamic[x], {0, 5}]
   , Dynamic[x]
   }]

When sliding the second slider, I would have though the first one one stay snapped until x > 0.3, but that is not the case: the first slider moves together with the second one.

Is the update function only evaluating when the first slider is moved?

Answer 1

You've only set the update function to snap in the first, so it will always show the current value of x and only when you dynamically change it using that slider, will the updating functionality be trickers causing it to snap. You can simply get what you are expecting by also including the snap functionality in the dynamically displayed value through:

DynamicModule[{x = 0},
 Column@{Slider[
  Dynamic[If[Abs[x- Round[x]] < 0.3, Round[x], x], 
      If[Abs[# - Round[#]] < 0.3, x = Round[x], x = #] &], {0, 5}]
, Slider[Dynamic[x], {0, 5}]
, Dynamic[x]
}]