How to check whether a method parameter is Nullable<> using reflection if it's also an "out" parameter?

Question

With method signatures like:

public interface TestInterface
{
    void SampleMethodOut(out int? nullableInt);
    void SampleMethod(int? nullableInt);
}

I'm using typeof(TestInterface).GetMethods()[1].GetParameters()[0].ParameterType to get the type, and then checking IsGenericType and Nullable.GetUnderlyingType. How can I do this with the method with the out parameter?

For the one that isn't an out parameter IsGenericType is true and Nullable.GetUnderlyingType returns Int32, but for the out parameter it's false and null. — NickL, Apr 05 '12 at 16:20
So for the non-out parameter, `ParameterType` returns `typeof(Nullable)` -- what does it return for the out parameter? — phoog, Apr 05 '12 at 16:23

score 3 · Accepted Answer · answered Apr 05 '12 at 16:15

3

Doh, ignore my previous answer.

You use Type.IsByRef, and call Type.GetElementType() if so:

var type = method.GetParameters()[0].ParameterType;
if (type.IsByRef)
{
    // Remove the ref/out-ness
    type = type.GetElementType();
}

answered Apr 05 '12 at 16:15

Jon Skeet

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score 1 · Answer 2 · answered Nov 14 '19 at 03:05

for everyone just finding this page

c# documentation pages show a concise way of doing just that
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types#how-to-identify-a-nullable-value-type

Console.WriteLine($"int? is {(IsNullable(typeof(int?)) ? "nullable" : "non nullable")} type");
Console.WriteLine($"int is {(IsNullable(typeof(int)) ? "nullable" : "non-nullable")} type");

bool IsNullable(Type type) => Nullable.GetUnderlyingType(type) != null;

// Output:
// int? is nullable type
// int is non-nullable type

Using reflection, this is how you get your parameter types:

typeof(MyClass).GetMethod("MyMethod").GetParameters()[0].ParameterType;

How to check whether a method parameter is Nullable<> using reflection if it's also an "out" parameter?

2 Answers2