Tikz incremental block diagram in beamer

beamertikz-pgf

I'm making a beamer presentation and within it I need a block diagram. I would like to incrementally generate the block diagram over multiple slides with a different text underneath it to explain what is happening. Is there a more efficient way to do this than replicating the code each frame?
Additionally is it possible to have a fixed position for the picture, rather than have it move up/down depending on the text underneath it?

MWE

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{matrix,graphs}
\usepackage{lipsum}
\begin{document}
\begin{frame}{System}
  \begin{tikzpicture}
    \matrix (m) [row sep = 2mm, column sep = 3mm, ampersand replacement=\&] {\node (A) [rectangle, draw] {A};\\
      \node (C) {\phantom{C}};\\
      };
  \end{tikzpicture}
  \begin{itemize}
  \item Now only block A is visible
  \end{itemize}
\end{frame}
\begin{frame}{System}
  \begin{tikzpicture}
    \matrix (m) [row sep = 2mm, column sep = 3mm, ampersand replacement=\&] {
      \node (A) [rectangle, draw] {A}; \& \node (B) [rectangle, draw] {B};\\
      \node (C) {\phantom{C}};\\
      };
      \graph [use existing nodes] {
        A -> B;
        };
  \end{tikzpicture}
  \begin{itemize}
  \item Block B is easy enough to add
  \end{itemize}
\end{frame}
\begin{frame}{System}
  \begin{tikzpicture}
    \matrix (m) [row sep = 2mm, column sep = 3mm, ampersand replacement=\&] {
      \node (A) [rectangle, draw] {A}; \& \node (B) [rectangle, draw] {B};\\
      \node (C) [rectangle, draw] {C};\\
      };
      \graph [use existing nodes] {
        A -> B;
        A -> C;
        };
  \end{tikzpicture}
  \begin{itemize}
  \item It's annoying to have to include \textbackslash phantom\{C\}
  \end{itemize}
\end{frame}
\begin{frame}{System}
  \begin{tikzpicture}
    \matrix (m) [row sep = 2mm, column sep = 3mm, ampersand replacement=\&] {
      \node (A) [rectangle, draw] {A}; \& \node (B) [rectangle, draw] {B};\\
      \node (C) [rectangle, draw] {C};\\
      };
      \graph [use existing nodes] {
        A -> B;
        A -> C;
        };
  \end{tikzpicture}
  \begin{itemize}
  \item Having a long text underneath also changes figure position which I don't want. \lipsum
  \end{itemize}
\end{frame}
\end{document}

Note: I won't have text as long as lipsum, my real block diagram and text should fit into one frame without any issue.

Thanks

Best Answer

Here is a solution:

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{matrix,graphs}
\usepackage{lipsum}
\begin{document}

\begin{frame}{System}
  \begin{tikzpicture}
    \matrix (m) [row sep = 2mm, column sep = 3mm, ampersand replacement=\&] {
      \node (A) [rectangle, draw] {A};
      \& \visible<2->{\node (B) [rectangle, draw] {B};}\\
      \visible<3->{\node (C) [rectangle, draw] {C};}\\
    };
    \visible<2->{\graph [use existing nodes] {A -> B;};}
    \visible<3->{\graph [use existing nodes] {A -> C;};}
  \end{tikzpicture}

  \begin{overprint}
    \onslide<1>
    \begin{itemize}
    \item Now only block A is visible
    \end{itemize}
    \onslide<2>
    \begin{itemize}
    \item Block B is easy enough to add
    \end{itemize}
    \onslide<3>
    \begin{itemize}
    \item Block C is easy enough to add
    \end{itemize}
    \onslide<4>
    \begin{itemize}
    \item \lipsum[6]
    \end{itemize}
  \end{overprint}
\end{frame}
\end{document}

enter image description here

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