CODEWITHSUNDEEP
c#genericsreflection
Simone
Simone

Reputation: 1337

How can I get an instantiated generic's parameter type?

I'm appalled I haven't found anything on the internet about this problem, but probably I'm looking for the wrong words. Here is what I need to do.

Suppose I have a generic type: List<string> works for the sake of simplicity. How do I get the parameter type (in this case typeof(string))?

Keep in mind that I need to do this from outside the generic class (not inside a class method, which is what I've seen in other SO questions). The bottom line is that I have an instance of a generic type, I need to know both its type AND its parameter type (in the example above, I would like to get both typeof(List) AND typeof(string), not anything like typeof(List<string>)). Of course, this must be done at runtime.

Thanks to everyone who will reply.

Upvotes: 3

Views: 444

Answers (4)

harpo
harpo

Reputation: 43228

It sounds like what you're looking for is Type.GetGenericArguments(). You would call it on the Type of the instance in question. It returns an array of Type (to Eric Lippert's chagrin).

Upvotes: 7

Osman Turan
Osman Turan

Reputation: 1371

typeof(List<string>).GetGenericArguments()[0]

Upvotes: 4

Krizz
Krizz

Reputation: 11552

Why won't you make your function generic? It will let compiler sort it out for you.

void your_func<T>(List<T> lst)
{
    Type list_type = typeof(List<T>);
    Type generic_list_type = typeof(List<>);
    Type generic_argument_type = typeof(T);
    // do what you need     
}

You can invoke it like normally:

var lst = new List<string>(); 
// ...
obj.your_func(lst);

Other option is to use reflection as described in other answers.

Upvotes: 1

Chris Shain
Chris Shain

Reputation: 51344

var myList = new List<String>();
var shouldBeString = myList.GetType().GetGenericArguments().FirstOrNull();
var shouldBeGenericList = myList.GetType().GetGenericTypeDefinition();

See http://msdn.microsoft.com/en-us/library/system.type.getgenericarguments.aspx and http://msdn.microsoft.com/en-us/library/system.type.getgenerictypedefinition.aspx respectively

Upvotes: 2

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