Remove the vspace reserved for the disappeared items in beamer

Question

I have a list in a beamer slide and for each item there must be a figure or an inner list, shown only in one slide. The problem is that, although the figure disappears, the space it used to occupied remains reserved for it. So, there is no room for the subsequent items.

How can I fix this?

I am currently using something like this:

\begin{frame}
   \begin{itemize}[<+->]
   \item Item 1
   \begin{itemize}[<.>]
    \item Item a
    \item Item b
    \item Item c
    \item Item d
    \item Item e
    \item Item f
    \item Item g
   \end{itemize}
   \item Item 2
   \begin{itemize}[<.>]
    \item Item a
    \item Item b
    \item Item c
    \item Item d
    \item Item e
    \item Item f
    \item Item g
   \end{itemize}
   \item Item 3
   \begin{itemize}[<.>]
    \item Item a
    \item Item b
    \item Item c
    \item Item d
    \item Item e
    \item Item f
    \item Item g
   \end{itemize}
  \end{itemize}
\end{frame}

Answer 1

You could use the \only<item_no> to achieve something like that

      \begin{frame}
           \begin{itemize}[<+->]
           \item Item 1
           \only<1>{
               \begin{itemize}[<.>]
                \item Item a
                \item Item b
                \item Item c
                \item Item d
                \item Item e
                \item Item f
                \item Item g
               \end{itemize}
               }
           \item Item 2
           \only<2>{
               \begin{itemize}[<.>]
                \item Item a
                \item Item b
                \item Item c
                \item Item d
                \item Item e
                \item Item f
                \item Item g
               \end{itemize}
           }
           \item Item 3
           \only<3> {
               \begin{itemize}[<.>]
                \item Item a
                \item Item b
                \item Item c
                \item Item d
                \item Item e
                \item Item f
                \item Item g
               \end{itemize}
           }
          \end{itemize}
    \end{frame}

This will collapse the inner list once you are done with it. I shared a working demo here