Lost bullets in a custom environment

Question

I have defined two custom enumitem environments with a grey background. The first one is for an inline itemize and a second one is for a normal itemize. The second one lost the bullets and I wonder why.

\documentclass[parskip=half]{scrbook}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}

\usepackage{tcolorbox}
\usepackage[inline, shortlabels]{enumitem}

% inline itemize
\newenvironment{inlineitem}[1][]
    {% begin-Befehle
        \begin{itemize*}[%
            %before=\hspace{1em},% Abstand vor dem ersten Aufzählungspunkt
            itemjoin=\hspace{1em},% Abstand zwischen zwei Aufzählungspunkten
            #1
        ]
    }
    {% end-Befehle
        \end{itemize*}%
    }
\newenvironment{MaterialInline}[1][]
    {% begin-Befehl
        \begin{tcolorbox}[%
            grow to left by=2mm,%
            left*=0mm,%
            grow to right by=2mm,%
            right*=0mm,%
            boxrule=0pt,% keine Rahmenlinie
            arc=0mm,% keinen Rundung in den Ecken
            ]%
        Material:~%
        \begin{itemize*}[%
            itemjoin=\hspace{1em},% Abstand zwischen zwei Aufzählungspunkten
            #1
        ]
    }
    {% end-Befehle
        \end{itemize*}%
        \end{tcolorbox}%
    }
\newenvironment{Material}[1][]
    {% begin-Befehl
        \begin{tcolorbox}[%
            grow to left by=2mm,%
            left*=0mm,%
            grow to right by=2mm,%
            right*=0mm,%
            boxrule=0pt,% keine Rahmenlinie
            arc=0mm,% keinen Rundung in den Ecken
            ]%
        \subsubsection{Material}
        \begin{itemize}[%
            #1
        ]
    }
    {% end-Befehle
        \end{itemize}%
        \end{tcolorbox}%
    }
\begin{document}


Done without a custom environment:


\begin{tcolorbox}[%
  grow to left by=2mm,%
  left*=0mm,%
  grow to right by=2mm,%
  right*=0mm,%
  boxrule=0pt,% keine Rahmenlinie
  arc=0mm,% keinen Rundung in den Ecken
  ]
  Material:~%
  \begin{inlineitem}
    \item Item 1
    \item Item 2
    \item Item 3
  \end{inlineitem}
\end{tcolorbox}

The following is done with the custom environment MaterialInline:


\begin{MaterialInline}
  \item Item 1
  \item Item 2
  \item Item 3
\end{MaterialInline}


Material without a custom environment:
\begin{tcolorbox}[%
  grow to left by=2mm,%
  left*=0mm,%
  grow to right by=2mm,%
  right*=0mm,%
  boxrule=0pt,% keine Rahmenlinie
  arc=0mm,% keinen Rundung in den Ecken
  ]
  \subsubsection{Material}
  \begin{itemize}
    \item Item 1
    \item Item 2
    \item Item 3
  \end{itemize}
\end{tcolorbox}


The following is done with the custom environment Material:
\begin{Material}
  \item Item 1
  \item Item 2
  \item Item 3
\end{Material}

\end{document}

Answer 1

By using

\begin{itemize}[%
            #1
        ]

the text (#1) becomes the label, so no bullets. (try with *~#1 to see what happens).

A correct definition would be

 ...
\subsubsection{Material}
    \begin{itemize}
    }
    {% end-Befehle
    \end{itemize}%
\end{tcolorbox}%
}

I guess when you add itemjoin= ... which is intended for the inline list, is ignored with everything that follows, and the correct vertical list is used.

You can also remove the #1 from the MaterialInline environment.

This is the complete code.

% !TeX TS-program = pdflatex


\documentclass[parskip=half]{scrbook}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}

\usepackage{tcolorbox}
\usepackage[inline, shortlabels]{enumitem}

% inline itemize
\newenvironment{MaterialInline}[1][]
{% begin-Befehl
    \begin{tcolorbox}[%
        grow to left by=2mm,%
        left*=0mm,%
        grow to right by=2mm,%
        right*=0mm,%
        boxrule=0pt,% keine Rahmenlinie
        arc=0mm,% keinen Rundung in den Ecken
        ]%
        Material:~%
        \begin{itemize*}[%
            itemjoin=\hspace{1em},% Abstand zwischen zwei Aufzählungspunkten
            ]
        }
        {% end-Befehle
        \end{itemize*}%
    \end{tcolorbox}%
}
\newenvironment{Material}[1][]
{% begin-Befehl
    \begin{tcolorbox}[%
        grow to left by=2mm,%
        left*=0mm,%
        grow to right by=2mm,%
        right*=0mm,%
        boxrule=0pt,% keine Rahmenlinie
        arc=0mm,% keinen Rundung in den Ecken
        ]%
        \subsubsection{Material}
        \begin{itemize} 
        }
        {% end-Befehle
        \end{itemize}%
    \end{tcolorbox}%
}
\begin{document}    
    
    The following is done with the custom environment MaterialInline:   
    
    \begin{MaterialInline}
        \item Item 1
        \item Item 2
        \item Item 3
    \end{MaterialInline}        
    
    The following is done with the custom environment Material:
    \begin{Material}
        \item Item 1
        \item Item 2
        \item Item 3
    \end{Material}
    
\end{document}

Answer 2

In definition for environment Material, you can determine if its optional argument is empty or not, and only use \begin{itemize}[#1] if #1 is non empty. For example

\usepackage{etoolbox} % already loaded by `tcolorbox`
\newenvironment{Material}[1][]
    {% begin-Befehl
        \begin{tcolorbox}[...]%
        \subsubsection{Material}
        \ifstrempty{#1}
          {\begin{itemize}}
          {\begin{itemize}[#1]}%
    }
    {% end-Befehle
        \end{itemize}%
        \end{tcolorbox}%
    }

This solves the missing-bullets problem, but introduces a minor new one: Now \begin{Material} \item ... is indistinguishable from \begin{Material}[] \item ... and you'll never be able to set an empty list label.

To overcome this, I recommend using xparse's arg-type o. It distinguishes "missing" (\begin{Material} \item ...) from "given by user" (\begin{Material}[<any value, even emtpy>] \item ...) for an optional argument.

\NewDocumentEnvironment{Material}{o}
    {% begin-Befehl
        \begin{tcolorbox}[...]%
        \subsubsection{Material}
        \IfValueTF{#1}
          {\begin{itemize}[#1]} % optional #1 is given by user
          {\begin{itemize}}     % optional #1 has no value
    }
    {% end-Befehle
        \end{itemize}%
        \end{tcolorbox}%
    }