c# reflection to invoke delegate method with unknown type

Question

// cant modiy this code, it's 3rd libray
public class TestClass{
    public void TestMethod(Class2 class2){
    }
    
    public void TestMethod(Class3 class3){
    }
}
public class Class2{}
public class Class3{}

var Class2Type = System.Reflection.Assembly.GetExecutingAssembly().GetType("Class2");
var TestMethodType = typeof(TestClass).GetMethod("TestMethod",new Type[] { Class2Type });
var del = TestMethodType.CreateDelegate(typeof(Action<,>).MakeGenericType(typeof(TestClass),Class2Type));
// how to invoke TestMethod using del?

if Class2 is a known type, we can invoke TestMethod using del like this:

var del = (Action<TestClass, Class2>)TestMethodType.CreateDelegate(typeof(Action<TestClass, Class2>));
del(new TestClass(), new Class2());

but if "Class2" is unkonwn dynamic string, I dont know how to do it?

sorry for my bad english.I created a code example that can be run online. https://sharplab.io/#v2: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

what do you mean with "unkonwn dynamic string"? Could you give us an example? — user3401335, Nov 13 '21 at 10:11
Well you need an instance of `Class2`. Do you have an instance of `Class2` at all? — Sweeper, Nov 13 '21 at 10:12
_".MakeGenericType"_ I don't see any generics in your example. — Jeroen van Langen, Nov 13 '21 at 10:16

Jeroen van Langen · Answer 1 · 2021-11-13T10:44:49.687

So, if I understand correctly, you are trying to invoke the right overload method, based on the type (which is not known compiletime)

In this case you cannot use generics, because the type isn't known. You will probably manage to create a generic type, based on the class2, but the next problem is calling it. So strongtyped in not the way. IMHO

You can just call Invoke on the MethodInfo.

Here is an example:

// search for the class2Type (I changed it a little so I can test it)
var class2Type = System.Reflection.Assembly.GetExecutingAssembly().GetType("TestProgram.Class2");

// Searching for the right (overloaded) method.
var testMethodType = typeof(TestProgram.TestClass).GetMethod("TestMethod", new Type[] { class2Type });

// create an instance of the TestClass (which is a known type)
var testClassInstance = new TestProgram.TestClass();

// create the instance of the class2 (which isn't a known type)
var class2Instance = Activator.CreateInstance(class2Type);

// invoke the testMethod and pass the class2 instance in it.
// you need to pass the testClassInstance also.
testMethodType.Invoke(testClassInstance, new[] { class2Instance });

yep, that's what I mean. but I want to use the CreateDelegate method instead of the Invoke method because it performs better. — tsdyy, Nov 15 '21 at 02:04
@tsdyy It would be better to create an ExpressionTree version. I have written an answer a while ago using expressiontrees. Here: https://stackoverflow.com/questions/840261/passing-arguments-to-c-sharp-generic-new-of-templated-type/39961349#39961349 — Jeroen van Langen, Nov 15 '21 at 07:31
thank you very much, but maybe I'm not understanding it right, I understand that even if you use an expression tree, you need a type-explicit delegate like ```public delegate void TestMethod(Class2 class2);```, but the 'Class2' is a dynamic string in my case. — tsdyy, Nov 16 '21 at 03:09

c# reflection to invoke delegate method with unknown type

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