tcolorbox 中的条件标题：当为空时不等同于无标题框

Question

考虑以下代码：

\documentclass[10pt]{article}
\usepackage{ifmtarg}
\usepackage{xcolor-material}
\usepackage[most]{tcolorbox}
\makeatletter
\newcommand{\makeboxtitle}[1]{\@ifmtarg{#1}{}{\textsc{\textbf{#1}\strut}}}
\makeatother
\newtcolorbox{untitledbox}{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
}
\newtcolorbox{titledbox}[1]{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
    title = \makeboxtitle{#1},
}
\begin{document}
\begin{untitledbox} This is an untitled box.\end{untitledbox}
\begin{titledbox}{} This is a titled box.\end{titledbox}
\begin{titledbox}{A title} This is a titled box.\end{titledbox}
\end{document}

产生以下结果：

问题是，即使没有指定标题，第二个框也不等同于第一个框（仍然会出现红色的空标题行）。如何修改命令\makeboxtitle或titledbox环境，以便当标题为空时，看起来就像没有标题一样？

Answer 1

您希望标题成为可选参数（因为它是在您的设置中是可选的）并使用xparse库：

\documentclass[10pt]{article}

\usepackage{xcolor-material}
\usepackage[most]{tcolorbox}
\tcbuselibrary{xparse}

\newtcolorbox{untitledbox}{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
}
\NewTColorBox{titledbox}{o}{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
    fonttitle=\scshape,
    IfValueT={#1}{title = \strut#1},
}

\begin{document}

\begin{untitledbox} This is an untitled box.\end{untitledbox}

\begin{titledbox} This is a titled box.\end{titledbox}

\begin{titledbox}[A title] This is a titled box.\end{titledbox}

\end{document}

请注意，这\bfseries\scshape不是通常的组合，对于大多数字体，您只会得到\bfseries。

您可以使用强制性参数来做到这一点，但我不认为这是最好的方法。

\documentclass[10pt]{article}

\usepackage{xcolor-material}
\usepackage[most]{tcolorbox}

\newtcolorbox{untitledbox}{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
}
\tcbset{
  my title/.code{
    \if\relax\detokenize{#1}\relax\else\tcbset{title=\strut#1}\fi
  },
}
\newtcolorbox{titledbox}[1]{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
    fonttitle=\scshape,
    my title={#1},
}

\begin{document}

\begin{untitledbox} This is an untitled box.\end{untitledbox}

\begin{titledbox}{} This is a titled box.\end{titledbox}

\begin{titledbox}{A title} This is a titled box.\end{titledbox}

\end{document}

Answer 2

无需使用ifmtarg，tcolorbox将检查空标题。您设置的方式tcolorbox不会找到空标题，而是会\makeboxtitle{}在标题中查找（这不是空的），因此将产生非空标题的输出（意味着标题的红色背景显示出来）。

现在\makeboxtitle{}将使用来\@ifmtarg检查标题是否为空，如果不是，将设置一些字体命令。相反，您可以使用键fonttitle来tcolorbox指定使用的字体，并tcolorbox决定标题何时为空。这就是以下内容：

\documentclass[10pt]{article}
\usepackage{xcolor-material}
\usepackage[most]{tcolorbox}
\newtcolorbox{untitledbox}{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
}
\newtcolorbox{titledbox}[1]{
    enhanced, breakable, sharp corners, center title,
    colframe = MaterialIndigo900,
    colback = MaterialIndigo50,
    colbacktitle = MaterialRed900,
    fonttitle = \scshape\bfseries\strut,
    title = {#1},
}
\begin{document}
\begin{untitledbox} This is an untitled box.\end{untitledbox}
\begin{titledbox}{} This is a titled box.\end{titledbox}
\begin{titledbox}{A title} This is a titled box.\end{titledbox}
\end{document}