Per-subsection figure numbering

Question

I want to have per-subsection figure numbering in the appendix of the following MWE: it should read "Figure A.1" instead of "Figure 2".

\documentclass{article}

\usepackage{amsmath}  
\numberwithin{equation}{section}

\usepackage[demo]{graphicx}   
\usepackage{caption}
\captionsetup[figure]{figurewithin=section}

\newcommand*{\appheading}[1][Appendix]{%
  \setcounter{secnumdepth}{0}\section{#1}\setcounter{secnumdepth}{3}%
  \renewcommand*{\thesubsection}{\Alph{subsection}}
  \numberwithin{equation}{subsection}  
}

\begin{document}

\section{Foo} 

\begin{equation}
  x = 4
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{foo}
  \caption{Fooo}
\end{figure}

\appheading
\appendix
\subsection{Baz}

\begin{equation}
  y = 3
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{baz}
  \caption{Baz}
\end{figure}

\end{document}

I tried changing the thefigure counter and also using the chngcntr package but couldn't make it work.

Answer 1

Use \numberwithin instead of the figurewithin option:

\documentclass{article}

\usepackage{amsmath}  
\numberwithin{equation}{section}

\usepackage[demo]{graphicx}   
\usepackage{caption}
\numberwithin{figure}{section}

\newcommand*{\appheading}[1][Appendix]{%
  \setcounter{secnumdepth}{0}\section{#1}\setcounter{secnumdepth}{3}%
  \renewcommand*{\thesubsection}{\Alph{subsection}}
  \numberwithin{equation}{subsection}
  \numberwithin{figure}{subsection}
}

\begin{document}

\section{Foo} 

\begin{equation}
  x = 4
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{foo}
  \caption{Fooo}
\end{figure}

\appheading
\appendix
\subsection{Baz}

\begin{equation}
  y = 3
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{baz}
  \caption{Baz}
\end{figure}

\end{document}

---

Why don't you use \part* instead of those tricks?

\documentclass{article}

\usepackage{amsmath}  
\numberwithin{equation}{section}

\usepackage[demo]{graphicx}   
\usepackage{caption}
\numberwithin{figure}{section}

\newcommand*{\appheading}[1][Appendix]{%
  \part*{#1}
  \renewcommand*{\thesection}{\Alph{section}}
}

\begin{document}

\section{Foo} 

\begin{equation}
  x = 4
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{foo}
  \caption{Fooo}
\end{figure}

\appheading
\appendix
\section{Baz}

\begin{equation}
  y = 3
\end{equation}

\begin{figure}[htbp!]
  \centering
  \includegraphics{baz}
  \caption{Baz}
\end{figure}

\end{document}

Answer 2

insert these two lines immediately after the line \subsction{Baz}:

\setcounter{figure}{0}
\setcounter{section}{1}