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I am reading an article about the MVVP Pattern and how to implement it with WPF. In the source code there are multiple lines where I cannot figure out what the question marks in it stand for.
private DateTime? _value;
What does the ? mean in the definition? I tried to find it in the help from VS but failed.
It’s a nullable value. Structs, by default, cannot be nullable, they must have a value, so in C# 2.0, the
Nullable<T>type was introduced to the .NET Framework.C# implements the
Nullable<T>type with a piece of syntactic sugar, which places a question mark after the type name, thus making the previously non-nullable type, nullable.