CODEWITHSUNDEEP
c#genericsreflection
tobiak777
tobiak777

Reputation: 3365

Invoke a generic method with a subtype of the generic parameter type

I am trying to invoke a generic method via reflection using a subtype of the generic parameter type. Here's the situation : 

public abstract class MyClass<T> where T : class
{
}

public static class Caller
{
    public static void Do<T>(MyClass<T> param1, string param2 = null) where T : class
    {

    }
}

public class ConcreteClass : MyClass<string>
{

}

However when I try to do :

ConcreteClass instance = Activator.CreateInstance(typeof(ConcreteClass));
MethodInfo methodInfo = typeof(Caller).GetMethod("Do");
methodInfo = methodInfo.MakeGenericMethod(typeof(ConcreteClass));
methodInfo.Invoke(null, new object[] { instance, Type.Missing });

I am getting an exception essentially saying :

Cannot convert type 'ConcreteClass' to type 'MyClass`[ConcreteClass]'

The exception message is very clear, however I don't seem to find how I can achieve what I am after.

Edit:

The compile time equivalent for what I am trying to achieve is :

Caller.Do(new ConcreteClass());

Which compiles fine.

Upvotes: 1

Views: 216

Answers (2)

Lee
Lee

Reputation: 144206

ConcreteClass extends MyClass<string> so you need to provide typeof(string) to MakeGenericMethod:

ConcreteClass instance = (ConcreteClass)Activator.CreateInstance(typeof(ConcreteClass));
MethodInfo methodInfo = typeof(Caller).GetMethod("Do");
methodInfo = methodInfo.MakeGenericMethod(typeof(string));
methodInfo.Invoke(null, new object[] { instance, Type.Missing });

Upvotes: 1

yaakov
yaakov

Reputation: 5850

Your reflection-based code is attempting to the runtime equivalent of Caller.Do<ConcreteClass>(instance, Type.Missing).

This is invalid. The method Do<> requires matching types - for Do<ConcreteClass>, you need an instance that is or is a subclass of MyClass<ConcreteClass>.

ConcreteClass is a subclass of MyClass<string>. For this, you would need to call Do<string>(instance), or overall, Caller.Do<string>(instance, Type.Missing).

Upvotes: 0

Related Questions