Using beamer overlays to set different styles in TikZ [duplicate]

Question

Possible Duplicate:
How to make beamer overlays with Tikz node

I'd like to draw a figure in TikZ for a beamer presentation, and color various nodes differently in different overlays of the same frame. I am able to use \only<> to put nodes and paths only in some overlays, using \only<>, but I can't seem to change styles using it.

Is it possible to change styles for different overlays? Can you think of a another way to color the nodes?

An example:

\documentclass{beamer}
\usepackage{pgf}
\usepackage{tikz}
\begin{document}
\begin{frame}{Frame}
  \begin{tikzpicture}
    \path (0,0) node[draw,rectangle] { 1 } --
          (2,0) node[draw,rectangle] { 2 } --
          (4,0) node[draw,rectangle] { 3 };
  \end{tikzpicture}
\end{frame}
\end{document}

Suppose I want to make the first node fill color become gray from the second overlay on, and the second node to become gray on the next overlay, and so on. How would you recommend doing it?

Answer 1

This is sort of annoying, since although the options are expanded, putting an \only in them will break; presumably, it contains some kind of non-expandable assignment. Therefore, it appears that the easiest solution is to define macros containing (or not) a color that you'd like to "uncover" on your nodes, and then conditionally redefine them using \only outside the options. To wit:

\documentclass{beamer}
%%% Unnecessary; tikz loads it
% \usepackage{pgf} 
\usepackage{tikz}
\begin{document}
\begin{frame}{Frame}
 \newcommand*\nodeonecolor{}
 \newcommand*\nodetwocolor{}
 \newcommand*\nodethreecolor{}
 \only<2->{\renewcommand*\nodeonecolor{red}}
 \only<3->{\renewcommand*\nodetwocolor{green}}
 \only<4->{\renewcommand*\nodethreecolor{blue}}
  \begin{tikzpicture}
    \path (0,0) node[draw,rectangle,\nodeonecolor] { 1 } --
          (2,0) node[draw,rectangle,\nodetwocolor] { 2 } --
          (4,0) node[draw,rectangle,\nodethreecolor] { 3 };
  \end{tikzpicture}
\end{frame}
\end{document}

See, \nodeonecolor (and others) starts empty, so the boxes are uncolored (black). Then, on slides 2, 3, and 4, these macros are defined to be other colors, so the node options are different even though the code itself is the same.