newcommand containing tikz node

Question

I am using tikz-qtree to draw a binary tree. As I need to have them labeled I wanted to ues the following macro which work in ordinary tikz:

\newcommand{\A}[1]{\node(a#1){Activity #1};}

However, this does not work; the error is that node is an undefined control sequence.

Of course this macro is used inside a tikzpicture, so basically I just want to dump \node(a1){Activity 1}; if \A{1} is called. I am pretty sure it has to do with my TeXnic. . . Maybe expansion?

Note, the tikz-qtree manual states that

\Tree specifically watches out for the token \node; do not use \path node or other equivalents.

Here is a minimal example:

\documentclass{minimal}
\usepackage{tikz,tikz-qtree}
\newcommand{\A}[1]{\node(a#1){Activity #1};}
\begin{document}
Works:\
\tikz\A{1};
\hfill
Works:
\Tree [.\node(a1){A1}; 1 2 ]
\hfill
Doesn't Work:
% \begin{tikzpicture}
%   \Tree [.\A{1} b c ]
% \end{tikzpicture}
\end{document}

Thanks,

Answer 1

As you suspected, the problem is related to expansion: \Tree is expanded first and looks for its parameters before expanding \A. The problem can be solved if \A is expanded first. The \expandafter primitive allows you to do this: the sequence

\expandafter<token1><token2>

is replaced by

<token1><expansion of token2>

and this replacement is reexamined by the expansion processor.

Since you also have to take into account the tokens [ and . you'll need three \expandafter commands:

\documentclass{article}
\usepackage{tikz,tikz-qtree}

\newcommand{\A}[1]{\node(a#1){Activity #1};}

\begin{document}

\expandafter\Tree \expandafter[\expandafter.\A{A} 1 2 ]

\begin{tikzpicture}
  \expandafter\Tree \expandafter[\expandafter.\A{1} b c ]
\end{tikzpicture}

\end{document}