How to call a generic method through reflection

Question

is it possible to call with reflection a method with "explict type argument" <S> definition
e.g. oObject.Cast<S>() ?

where is:

IList <P> oObject = new List <P>();

I tried with

oObject.getType().InvokeMember( "Cast", BindingFlags.InvokeMethod, null, oObject, null)

but it does not work, does anyone know why?

Here is the complete test code but still it does not work. The last line produce always exception. Is it possible to make it work ?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;

namespace reflection_tester
{
    class CBase
    {
        public string Ja = "I am the base";
    }

    class MyClass01 : CBase
    {
        public string _ID;

        public string ID
        {
            get { return _ID; }
            set { _ID = value; }
        }
    }

    class Program
    {

        public static object wrapper()
        {
            //return a list of classes MyClass01

            IList<MyClass01> lstClass01 = new List<MyClass01>();

            MyClass01 oClass01a = new MyClass01();
            oClass01a.ID = "1";

            MyClass01 oClass01b = new MyClass01();
            oClass01b.ID = "2";

            lstClass01.Add(oClass01a);
            lstClass01.Add(oClass01b);

            return lstClass01;
        }

        static void Main(string[] args)
        {

            MyClass01 oMy1 = new MyClass01();
            oMy1._ID = "1";

            MyClass01 oMy2 = new MyClass01();
            oMy2._ID = "3";

            IList<MyClass01> oListType01 = new List<MyClass01>();

            oListType01.Add(oMy1);
            oListType01.Add(oMy2);

            object oObjectType = new object();

            oObjectType = oListType01;

            /* this works */
            IEnumerable<CBase> enumList = oListType01.Cast<CBase>();

            MethodInfo mInfo = typeof(System.Linq.Enumerable).GetMethod("Cast", new[] { typeof(System.Collections.IEnumerable) }).MakeGenericMethod(typeof(CBase));

            /* this does not work, why ? throws exception */
            IEnumerable<CBase> enumThroughObject = (IEnumerable<CBase>)mInfo.Invoke(oObjectType, null);

            return;
        }
    }
}

Rob Fonseca-Ensor · Accepted Answer · 2009-12-23T12:30:08.540

15

The Cast extension method lives on the class Enumerable, and you need to call MakeGenericMethod:

typeof(System.Linq.Enumerable)
    .GetMethod("Cast", new []{typeof(System.Collections.IEnumerable)})
    .MakeGenericMethod(typeof(S))
    .Invoke(null, new object[] { oObjectType })

update: Because the method is static, the first parameter to Invoke should be null

edited Dec 23 '09 at 12:30

answered Dec 21 '09 at 17:00

Rob Fonseca-Ensor

15,510
44
57

Invoke function does not take one parameter so if I put second parameter as "null"I am getting exception. any clue why ? – milan Dec 21 '09 at 17:52
Exception getting is: Invalid number of parameters. – milan Dec 21 '09 at 17:58
`Enumerable.Cast()` does not take any "arguments". The argument given in this case is the object you want to call the extension method Cast on. – user7116 Dec 21 '09 at 18:07
but there is no Invoke with just one parameter!? – milan Dec 21 '09 at 18:17
I must give 2 or more parameters... – milan Dec 21 '09 at 18:18
1

@milan: Apologies, it appears @Rob's code is slightly incorrect. You would call `.Invoke(null, oObject)` since Cast is static, per MSDN. http://msdn.microsoft.com/en-us/library/a89hcwhh.aspx – user7116 Dec 21 '09 at 18:26
please see below for comments it still does not work.... – milan Dec 22 '09 at 13:10
it's `.Invoke(null, oObject)` not `.Invoke(oObject, null)` – Rob Fonseca-Ensor Dec 22 '09 at 15:03
Also can I recommend that whenever you get an exception, you tell us what the exception is (exactly) and also, if you need to update your question don't add a new "answer" - just edit the old question – Rob Fonseca-Ensor Dec 22 '09 at 15:06
I dont know where to write any more :) it just does not work in any combination. If possible please try code which I copied down(because code is too big to fit this small edit box). Combination you propose is not compilable! so Invoke(null, oObject) is not compilable any more ideas? or we should just quit ? – milan Dec 22 '09 at 16:59
IT WORKS!!!! sorry for asking so much qestions, the answer is that Invoke should have list in which the only element is oObjectType. I tried always without list and failed. Many thans to all ! d.Invoke(null, new object[] { oObjectType }) br, Milan. – milan Dec 22 '09 at 17:16
Thanks Milan, i'll update my answer – Rob Fonseca-Ensor Dec 23 '09 at 12:29

score 0 · Answer 2 · answered Dec 21 '09 at 16:55

0

I think you're looking for Type.MakeGenericType

answered Dec 21 '09 at 16:55

Jamiec

133,658
13
134
193

3

I am sorry but I do not understand such short explanation, could you please write some code in order to understand it better ? – milan Dec 21 '09 at 18:02

How to call a generic method through reflection

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