Finding out if a type implements a generic interface

user_130658 0
Viewed 22788

Let's say I have a type, MyType. I want to do the following:

  1. Find out if MyType implements the IList interface, for some T.
  2. If the answer to (1) is yes, find out what T is.

It seems like the way to do this is GetInterface(), but that only lets you search by a specific name. Is there a way to search for "all interfaces that are of the form IList" (If possible it woudl also be useful if it worked if the interface was a subinterface of IList.)

Related: How to determine if a type implements a specific generic interface type

reflection .net c#
7 Answers
// this conditional is necessary if myType can be an interface,
// because an interface doesn't implement itself: for example,
// typeof (IList<int>).GetInterfaces () does not contain IList<int>!
if (myType.IsInterface && myType.IsGenericType && 
    myType.GetGenericTypeDefinition () == typeof (IList<>))
    return myType.GetGenericArguments ()[0] ;

foreach (var i in myType.GetInterfaces ())
    if (i.IsGenericType && i.GetGenericTypeDefinition () == typeof (IList<>))
        return i.GetGenericArguments ()[0] ;

Edit: Even if myType implements IDerivedFromList<> but not directly IList<>, IList<> will show up in the array returned by GetInterfaces().

Update: added a check for the edge case where myType is the generic interface in question.

Anton_Tykhyy_777240

Using reflection (and some LINQ) you can easily do this:

public static IEnumerable<Type> GetIListTypeParameters(Type type)
{
    // Query.
    return
        from interfaceType in type.GetInterfaces()
        where interfaceType.IsGenericType
        let baseInterface = interfaceType.GetGenericTypeDefinition()
        where baseInterface == typeof(IList<>)
        select interfaceType.GetGenericArguments().First();
}

First, you are getting the interfaces on the type and filtering out only for those that are a generic type.

Then, you get the generic type definition for those interface types, and see if it is the same as IList<>.

From there, it's a simple matter of getting the generic arguments for the original interface.

Remember, a type can have multiple IList<T> implementations, which is why the IEnumerable<Type> is returned.

user_507760

If i understand your question correctly, this is what you are trying to do. If not, please explain further.

public class MyType : ISomeInterface
{
}

MyType o = new MyType();

if(o is ISomeInterface)
 {
 }

edit: if you change your question, please add the fact that you edited..because now my answer looks like it doesn't belong.

In that case, here is a very large LINQ

            var item = typeof(MyType).GetInterfaces()
                            .Where(x => x.IsGenericType && x.GetGenericTypeDefinition() == typeof(IList<>))
                            .Select(t => t.GetGenericArguments().First())
                            .FirstOrDefault();

if( item != null )
 //it has a type
user_1199290
Chris_Ballance_15510
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