Question

If I have the class name of the user defined object as a string how do I use it in a generic function as Type of the object ?

SomeGenericFunction(objectID);

Answer 1

If you have a string, then the first thing to do is to use Type.GetType(string), or (preferably) Assembly.GetType(string) to get the Type instance. From there, you need to use reflection:

Type type = someAssembly.GetType(typeName);
typeof(TypeWithTheMethod).GetMethod("SomeGenericFunction")
          .MakeGenericMethod(type).Invoke({target}, new object[] {objectID});

where {target} is the instance for instance methods, and null for static methods.

For example:

using System;
namespace SomeNamespace {
    class Foo { }
}
static class Program {
    static void Main() {
        string typeName = "SomeNamespace.Foo";
        int id = 123;
        Type type = typeof(Program).Assembly.GetType(typeName);
        object obj = typeof(Program).GetMethod("SomeGenericFunction")
            .MakeGenericMethod(type).Invoke(
                null, new object[] { id });
        Console.WriteLine(obj);
    }
    public static T SomeGenericFunction<T>(int id) where T : new() {
        Console.WriteLine("Find {0} id = {1}", typeof(T).Name, id);
        return new T();
    }
}