Finding out if a type implements a generic interface


C# Problem Overview

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

C# Solutions

Solution 1 - C#

// 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.

Solution 2 - C#

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

public static IEnumerable<Type> GetIListTypeParameters(Type type)
    // Query.
        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.

Solution 3 - C#

    public static bool Implements<I>(this Type type) where I : class
         if (!typeof(I).IsInterface)
             throw new ArgumentException("Only interfaces can be 'implemented'.");

         return typeof(I).IsAssignableFrom(type);

Solution 4 - C#

Using Anton Tykhyy's proposal, here is a small Extension Method to check if some type implements a generic interface with one given generic type parameters:

public static class ExtensionMethods
    /// <summary>
    /// Checks if a type has a generic interface. 
    /// For example 
    ///     mytype.HasGenericInterface(typeof(IList<>), typeof(int)) 
    /// will return TRUE if mytype implements IList<int>
    /// </summary>
    public static bool HasGenericInterface(this Type type, Type interf, Type typeparameter)
        foreach (Type i in type.GetInterfaces())
            if (i.IsGenericType && i.GetGenericTypeDefinition() == interf)
                if (i.GetGenericArguments()[0] == typeparameter)
                    return true;

        return false;

Solution 5 - C#

As a helper method extension

public static bool Implements<I>(this Type type, I @interface) where I : class  
    if(((@interface as Type)==null) || !(@interface as Type).IsInterface)
        throw new ArgumentException("Only interfaces can be 'implemented'.");

    return (@interface as Type).IsAssignableFrom(type);

example usage:

var testObject = new Dictionary<int, object>();
result = testObject.GetType().Implements(typeof(IDictionary<int, object>)); // true!

Solution 6 - C#

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())

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

Solution 7 - C#

Type[] typeArray2 = c.GetInterfaces();
for (int num2 = 0; num2 < typeArray2.Length; num2++)
     if (this == typeArray2[num2])
          return true;



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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionAlex319View Question on Stackoverflow
Solution 1 - C#Anton TykhyyView Answer on Stackoverflow
Solution 2 - C#casperOneView Answer on Stackoverflow
Solution 3 - C#user989279View Answer on Stackoverflow
Solution 4 - C#KnasterbaxView Answer on Stackoverflow
Solution 5 - C#GenericProgrammerView Answer on Stackoverflow
Solution 6 - C#Stan R.View Answer on Stackoverflow
Solution 7 - C#Chris BallanceView Answer on Stackoverflow