Keep itemize items in fixed position when changing slides with subitems

Question

I have some itemize items that I want to present sequentially. I also want to discuss each item, using for that subitems. The subitems should disappear after that item is discussed.

I can achieve this using \only commands for each batch of subitems, see the example below:

\documentclass{beamer}

\begin{document}
\begin{frame}[t]
    \begin{itemize}
        \item<1-> Item 1
        \only<2>{\begin{itemize}
            \item Subitem 1
            \item Subitem 2
        \end{itemize}}
        \item<3-> Item 2
        \only<4>{\begin{itemize}
            \item Subitem 1
            \item Subitem 2
        \end{itemize}}
        \item<5-> Item 3
        \only<6>{\begin{itemize}
            \item Subitem 1
            \item Subitem 2
        \end{itemize}}
    \end{itemize}
\end{frame}

I want the main Items (Item 1, Item 2, etc.) to have a fixed position, rather than shifting vertically as I transition from one slide to the other (this is the reason why I used the [t] specifier for the frame environment). However, whenever I transition into a slide that has a subitem (say, in slide 4), the vertical spacing between the main items gets messed up.

Is there a way of achieving what I want? I have tried using overlayarea and overprint for this, but I was not able to do it.

Answer 1

\documentclass{beamer}

\begin{document}
\begin{frame}[t]
    \begin{itemize}
        \item<1-> Item 1
        \begin{itemize}[<only@2>]
            \item Subitem 1
            \item Subitem 2
        \end{itemize}
        \item<3-> Item 2
        \begin{itemize}[<only@4>]
            \item Subitem 1
            \item Subitem 2
        \end{itemize}
        \item<5-> Item 3
        \begin{itemize}[<only@6>]
            \item Subitem 1
            \item Subitem 2
        \end{itemize}
    \end{itemize}
\end{frame}
\end{document}