Mouseover & Dynamic in Mathematica

Question

Could anyone point out why this is not working in Mathematica 8:

DynamicModule[{x = Pink},
 Row[
  {Style["Hello", x],
   Mouseover[
    x = Green; "World",
    x = Blue; "World"]}]]

What I expect is to see the color of "Hello" change when I mouse over "World". What I am getting is a pink "Hello" that never changes color.

Answer 1

A quick check shows that Mouseover evaluates all the expressions inside of it when you first launch it:

Mouseover[Print["One"]; 1, Print["Two"]; 2]

The idiomatic way of actually making the Mouseover modify the values of x is to use MouseAnnotation. Mr. Wizard's answer describes how to achieve this.

Answer 2

If you look at the FullForm of the result, you'll see that it only contains the last part of each compound instruction set. Apparently Mouseover evaluates its arguments and only stores the results.

Answer 3

As an alternative you could do something like

DynamicModule[{col = Pink}, 
 Row[{Style["Hello ", FontColor -> Dynamic[col]], 
   Dynamic@If[CurrentValue["MouseOver"],
     col = Green; "World", 
     col = col /. Green -> Blue; "World"]}]
] 

Answer 4

I think I have waited long enough to be fair. Here is my proposal:

DynamicModule[{x = Pink},
 Row[{
   Dynamic@Style["Hello", If[MouseAnnotation[] === 1, x = Green; Blue, x]],
   Annotation["World", 1, "Mouse"]
 }]
]

Answer 5

Try using EventHandler with "MouseEntered" and "MouseExited":

DynamicModule[{c = Pink}, Row[{
 Style["Hello", FontColor -> Dynamic[c]], 
 EventHandler[
  "World", {
   "MouseEntered" :> (c = Blue), 
   "MouseExited" :> (c = Green)
}]}]]