Question

I have a method with a signature

string GenericMethod<T>();

Usually you’d call this simply with:

var result = GenericMethod<AType>();

However, that doesn’t work for my case because AType is passed to the parent method as a Type.

There’s code below which shows where I’ve got to. Currently it errors as //ERROR HERE.

Before the code, quick explanation: TestClass implements both ITestClass and INotTestClass. This is important because the point here is, if I am passed a TestClass, I would want to invoke the method with ITestClass, not INotTestClass.
TestClass has a method that simply returns the name of the type in its generic brackets.

Ok, here’s the code in the form of a Unit test.

using System;
using NUnit.Framework;

namespace Ian.Tests
{   
    [TestFixture]
    public class MiscTests
    {
        [Test]
        public void WhoWeCallingTest()
        {
            var i = new TestClass();
            i.TestGetTheType();
        }
    }

    public class TestClass : ITestClass, INotTestClass
    {
        public void TestGetTheType()
        {
            var t1 = typeof(ITestClass);
            var t2 = typeof(INotTestClass); 

            var t = GetType();

            // so I can make a delegate normally, but no use as I don't have this info usually.
            var dummyFunc = new MyDelegate<ITestClass>(GetTheType<ITestClass>);


            var methodInfo = t.GetMethod("GetTheType");
            var baseType = typeof(MyDelegate<>);
            var delType = baseType.MakeGenericType(t1);
            //ERROR HERE.
            var del = Delegate.CreateDelegate(delType, this, methodInfo);
            del.Method.Invoke(this, null);

        }

        public delegate string MyDelegate<T>();

        public string GetTheType<T>()
        {
            return typeof(T).Name;
        }
    }

    public interface ITestClass { }

    public interface INotTestClass { }
}

Answer 1

You need to use MethodInfo.MakeGenericMethod to construct the appropriate method:

var methodInfo = t.GetMethod("GetTheType");
var methodWithType = methodInfo.MakeGenericMethod(t1);
methodWithType.Invoke(this, null);