会话变量引用后的问号(?)-这是什么意思 [英] Question Mark (?) after session variable reference - What does that mean

问题描述

我有一个代码片段可以修改.在这里，我发现了这种语法.

I have had a code snippet comes to modify. In there i found this such syntax.

Session("LightBoxID")?.ToString()

我不明白问号(?)是什么意思.谷歌搜索没有帮助我任何提示

I didn't understand what is that Question mark (?) there means. No googling helped me about any hint

推荐答案

在尝试调用 .ToString()<之前，它会对 Session("LightBoxID")进行空检查./code>.

It performs a null-check on Session("LightBoxID") before attempting to call .ToString() on it.

MS Docs:

MS Docs: Null-conditional operators ?. and ?[]

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