List<Int16>? as an method parameter

Question

Error message cannot have non-nullable parameter

How can I pass a List? to a method?

public int RegexAutoCode(int sID, List<Int16>? valueIDs, string text, SqlCommand cmd)

Answer 1

There's no such thing as a List<>? - List is a reference type regardless of the element type, and so is already nullable:

// This is absolutely fine
List<Int16> list = null;

If you wanted a List of nullable Int16 values (so each element can be null or an Int16 ) then you want a parameter like this:

List<Int16?> valueIDs

For Nullable<T> to be valid, T has to be a non-nullable value type. That's what the T : struct constraint indicates.

Answer 2

Use List<Int16?>

You had the ? in the incorrect place.