Get the Type of a generic Interface?

Question

I got a generic Interface like this :

public interface IResourceDataType<T>
{
    void SetResourceValue(T resValue);
}

Then I got this class that implements my Interface :

public class MyFont : IResourceDataType<System.Drawing.Font>
{
    //Ctor + SetResourceValue + ...
}

And finally I got a :

var MyType = typeof(MyFont);

I, now, want to get the System.Drawing.Font Type from MyType ! At the moment, I got this code :

if (typeof(IResourceDataType).IsAssignableFrom(MyType))
{
    //If test is OK
}

But I don't manage to "extract" my Type here... I tried a couple of things with GetGenericArguments() and other things but they either don't compile or return a null value/List... What do I have to do ?

EDIT : Here is the solution that fit my code for those who will get the same problem :

if (typeof(IResourceDataType).IsAssignableFrom(MyType))
{
    foreach (Type type in MyType.GetInterfaces())
    {
        if (type.IsGenericType)
            Type genericType = type.GetGenericArguments()[0];
        }
    }
}

Have you seen this post: http://stackoverflow.com/questions/557340/c-sharp-generic-list-t-how-to-get-the-type-of-t — Brad Christie, Jan 16 '12 at 14:30
Yep, and a couple of another ones, they don't answer to my question... My feeling is that I have to use GetInterfaces() and do some other things, I'm actually trying it ! — Guillaume Slashy, Jan 16 '12 at 14:32

Frédéric Hamidi · Accepted Answer · 2014-03-30T08:16:12.373

13

Since your MyFont class only implements one interface, you can write:

Type myType = typeof(MyFont).GetInterfaces()[0].GetGenericArguments()[0];

If your class implements several interfaces, you can call the GetInterface() method with the mangled name of the interface you're looking for:

Type myType = typeof(MyFont).GetInterface("IResourceDataType`1")
                            .GetGenericArguments()[0];

edited Mar 30 '14 at 08:16

answered Jan 16 '12 at 14:32

Frédéric Hamidi

258,201
41
486
479

That's what I'm trying, but I do implement multi-interfaces, that was just a snippet to expose my problem ! – Guillaume Slashy Jan 16 '12 at 14:33
I'll "EDIT" with the final solution, I'm close to it – Guillaume Slashy Jan 16 '12 at 14:34
You'll have to use `GetInterface()` then, see my updated answer. – Frédéric Hamidi Jan 16 '12 at 14:36
Used "IsGeneric", see the Solution is my question :) thanks for ur help anyway ! – Guillaume Slashy Jan 16 '12 at 14:38
In fact your solution is the good one Frederic, but is there a way to get something more robust than just a string ? I mean, if I rename my Interface, the compiler won't say anything with your code :/ – Guillaume Slashy Jan 17 '12 at 13:07
I don't know if it really qualifies as *more robust*, but [FindInterfaces()](http://msdn.microsoft.com/en-us/library/system.type.findinterfaces.aspx) takes a filter delegate and a criteria argument instead of a string, so you can implement the search algorithm yourself is you wish to do so. – Frédéric Hamidi Jan 17 '12 at 13:15

score 6 · Answer 2 · answered Jan 26 '18 at 21:37

var fontTypeParam = typeof(MyFont).GetInterfaces()
    .Where(i => i.IsGenericType)
    .Where(i => i.GetGenericTypeDefinition() == typeof(IResourceDataType<>))
    .Select(i => i.GetGenericArguments().First())
    .First()
    ;

This takes care of you concern about renaming the interface. There's no string literal, so a rename in Visual Studio should update your search expression.

Get the Type of a generic Interface?

2 Answers2