Animate Line / Path using Tikz and 'animate' package

Question

I would like to animate the following path from A to B.

\begin{tikzpicture}
\draw [->, draw=black!70, line width=2.5] (8,4) -- +(1,0) node (v4) {} -- +(1,-2) -- +(0,-2);
\node at (7.5,4) {A};
\node at (7.5,2) {B};
\end{tikzpicture}

Something similar to the code AlexG provided in Animating Protocols

\documentclass{beamer}
\usepackage{tikz} 
\usepackage{animate} 
\begin{document} 
\begin{frame} 
\begin{animateinline}[autoplay,loop]{3} 
\multiframe{10}{rPos=0.1+0.1}{ 
\begin{tikzpicture}[] 
\node (s){A}; \node (r) at (1,0) {}; 
\node (t) at (1,-2) {}; 
\node (v) at (0,-2) {B}; 
\path (s) -- (r) -- (t)--(v) node[pos=\rPos,coordinate] (p) {}; 
\draw[->, draw=black!70, line width=2.5] (s) -- +(r)--+(t)--+(p); 
\end{tikzpicture} 
} 
\end{animateinline} 
\end{frame} 
\end{document}

Answer 1

Next code uses Jake's answer to How to animate a path or how to draw starting fraction of a complex but linear path? adapted to your path form A to B. It draws the start segment of a path with an arrow at the end and moving along the animation.

As soon as I can understand how to convert the animation to an animated gif, I'll upload the image. I know it's explained here, but I've never tried it.

\documentclass{beamer}
\usepackage{animate}
\usepackage{tikz}
\usetikzlibrary{calc,decorations,arrows,positioning,matrix}

% A simple empty decoration, that is used to ignore the last bit of the path
\pgfdeclaredecoration{ignore}{final}
{
\state{final}{}
}

\pgfdeclaremetadecoration{start}{initial}{
    \state{initial}[
        width={0pt},
        next state=middle
    ]
    {\decoration{moveto}}

    \state{middle}[
        width={\pgfmetadecoratedpathlength*\pgfdecorationsegmentlength},
        next state=final
    ]
    {\decoration{curveto}}

    \state{final}
    {\decoration{ignore}}
}

\tikzset{%
 start segment/.style={decoration={start,raise=2mm},decorate, segment length=#1},
}

\begin{document}

\begin{frame}
\begin{animateinline}[autoplay,loop]{3} 
\multiframe{10}{rPos=0.15+0.1}{ 
\begin{tikzpicture}[] 
\node (s){A}; \node (r) at (1,0) {}; 
\node (t) at (1,-2) {}; 
\node (v) at (0,-2) {B}; 
\draw[start segment=\rPos,->,black!70, line width=2.5] (s) -- (r.center) -- (t.center)--(v); \end{tikzpicture} 
} 
\end{animateinline} 
\end{frame} 
\end{document}

Answer 2

You can also use uncover for this job (though the code is not tidy as when using foreach)

\documentclass{beamer}
\usepackage{tikz}

\begin{document}

\begin{frame}
\begin{tikzpicture}
\node at (7.5,4) {A};
    \uncover<2->{\draw [-, draw=black!70, line width=1] (8,4) -- +(1,0) coordinate (v4) {} ;}
    \uncover<3->{\draw [-, draw=black!70, line width=1] (v4) -- +(0,-2) coordinate (v5) {} ;}
    \uncover<4->{\draw [->, draw=black!70, line width=1] (v5) -- +(-1,0) ;}
\uncover<5->{ \node at (7.5,2) {B};}
\end{tikzpicture}
\end{frame}

\end{document}

Answer 3

The one-page animation which loops:

\documentclass{beamer}
\usepackage{tikz}
\usepackage{animate}
\usepackage{fancyvrb}
\begin{VerbatimOut}{timeline.txt}
::0x0 % A
::1x0 % --
::2x0 % |
::3x0 % <--
::4   % B
\end{VerbatimOut}

\begin{document}

\begin{frame}
\begin{animateinline}[
  timeline=timeline.txt,
  begin={
    \begin{tikzpicture}
    \useasboundingbox (7.3,1.8) rectangle (9.1,4.2);
  },
  end={\end{tikzpicture}},
  loop,autoplay
]{1}
    \node at (7.5,4) {A};
\newframe
    \draw [-, draw=black!70, line width=1] (8,4) -- +(1,0) coordinate (v4) {};
\newframe
    \draw [-, draw=black!70, line width=1] (v4) -- +(0,-2) coordinate (v5) {};
\newframe
    \draw [->, draw=black!70, line width=1] (v5) -- +(-1,0);
\newframe
    \node at (7.5,2) {B};
\end{animateinline}
\end{frame}

\end{document}