为什么我们在 C# 中使用可空字符串？

Question

In Microsoft official Learning Module "Create a Web API with ASP.NET Core" Why some sample codes use nullable string type although we know strings are nullable in itself since it is a reference type? See Model/Pizza.cs class in this tutorial .

Answer 1

In C# 8.0, a new language feature was introduced for nullable reference types which was intended to help remove the whole class of problems around accidentally dereferencing null objects.

By assuming that all reference types are not actually nullable, the compiler can flag up suspicious code based on its own analysis of how null values may propagate through the code.

The ? annotations you see in the tutorial are indications of what fields/properties etc. are allowed to contain null and therefore need to be checked as such before doing anything with them.