How can I apply a style to existing tikz node on specific slides

Question

This is what I'm trying to do

    \begin{tikzpicture}
    [node distance = 1cm, auto,font=\footnotesize,
    % STYLES
    every node/.style={node distance=1.3cm},
    comment/.style={rectangle, inner sep= 5pt, text width=4cm, node distance=0.25cm, font=},
    module/.style={rectangle, drop shadow, draw, fill=black!10, inner sep=5pt, text width=3cm, text badly centered, minimum height=0.8cm, font=\bfseries\footnotesize\sffamily,rounded corners},
    selected/.style={fill=red!40}]

    \node [module] (nodeA) {node A};
    \node [module, below of=nodeA] (nodeA) {node B};

    \only<1>{
      \node [comment, text width=6cm, right=0.25 of nodeA] {short description of Node A};
      \node [comment, text width=6cm, right=0.25 of nodeB] {short description of Node B};
     }

    \only<2>{
      \node [selected] (nodeA) {};
      \node [comment, text width=6cm, right=0.25 of nodeA] {long description of node A};
    }
    \only<3>{
      \node [selected] (nodeB) {};
      \node [comment, text width=6cm, right=0.25 of nodeA] {long description of node B};
    }
    \end{tikzpicture}

The problem is

      \node [selected] (nodeB) {};

creates a new node, but I want it to apply the style for the existing node. Is there any way to do so?

Of course I could have copies of every node in selected state and not-selected state, but I really want to have a normal solution.

Answer 1

I don't think you can do this the way you want to (assuming I understand the question correctly), because once a node is drawn, there's no way to change its appearance. I'd suggest using Beamer's \alt macro:

\alt<2>{\node[module,selected] at (nodeA) {node A};}{\node[module] at (nodeA) {node A};}
\alt<3>{\node[module,selected] at (nodeB) {node B};}{\node[module] at (nodeB) {node B};}
\node[comment,text width=6cm,right=0.25 of nodeA]{\alt<2>{short description}{long description}};
\node[comment,text width=6cm,right=0.25 of nodeB]{\alt<3>{short description}{long description}};

Or something like that (you might have to tinker with the semicolons to get it to work, I can't test that at the moment).

Another option would be to actually just draw a new node. If you include

\node[module,selected] at (nodeA) {node A};

inside \only<2>, that will draw a node that looks just like node A, except with a red background, at the same position at node A. The new node will cover up the original node A.

Answer 2

Sometimes, to avoid repetitions, it may be nice to do something like this:

% #1    Overlay specs.
% #2    Style name.
% #4    Style properties.
\def\onlystyle<#1>#2#3{%
    \alt<#1>{%
        \tikzset{#2/.style = {#3}}
    }{%
        \tikzset{#2/.style = {}}
    }%
}

Then, if you put, for example, this within a frame:

\onlystyle<2>{selected}{fill = red}

the style selected will be defined as fill = red on the second slide of the animation, and as a style with no effect whatsoever on every other slide. Then, you can write a readable figure such as:

\begin{tikzpicture}
    \node           at (0, 0) {A};
    \node[selected] at (1, 0) {B};
    \node           at (2, 0) {C};
\end{tikzpicture}

and the “B” node will be highlighted on the second slide. This way, you don't have to copy-paste tons of node definitions. Of course, it cannot be applied to every single animation need, but I like to keep this technique up my sleeve.