英文:
C# - contains throws null exception
问题
如果 SegroupOf 为 null，如何处理？我已将 SegroupOf 声明为可为空 (nullable)，如何确保即使它为 null，也不会引发任何错误？
英文:
My code
string? SegroupOf;
if(SegroupOf.Contains("Team"))
{
}
If SegroupOf is null it throws an error. How to handle null? I have given SegroupOf as nullable, how to make sure even if its null it doesnot throw any error
答案1
得分: 5
你可以这样使用null-conditional-operator：
if(SegroupOf?.Contains("Team") == true)
然而，由于 SegroupOf?.Contains 返回 bool? 而不是 bool，您需要将结果与 bool 值 true 进行比较。
您还可以使用传统的空检查：
if(Segroup != null && Segroup.Contains("Team"))
然而，这与空条件操作符略有不同，因为空条件操作符是短路的，意味着 Segroup 只被访问一次，而在第二种情况下被访问两次。
英文:
You can use the null-conditional-operator like so:
if(SegroupOf?.Contains("Team") == true)
However as SegroupOf?.Contains returns a bool? instead of bool, you need to compare the result to the bool-value true.
You can also just use old-school null-check:
if(Segroup != null && Segroup.Contains("Team"))
However that is slightly different as the null-conditional is short-circuiting, meaning Segroup is only accessed once, while in the second case it's accessed two times.
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