Reflection issue

Question

Suppose I have an interface called IVerifier

public interface IVerifier
{
  bool Validate(byte[]x, byte[]y);
}

and I had to load an assembly by reflection, and that assembly holds the same signature, how possible it is to do this:

IVerifier c = GetValidations();
c.Validate(x,y);

And inside GetValidations() is the reflection resides!

I've been thinking about this a lot, and all I get is that invoking the reflected method is going to be inside GetValidations(), but it must be away to do it like above.

Use the Assembly.CreateInstance() method to create an object of the class that implements IVerifier. You'll need a good guess at the name of the class that implements it. Or iterate the types in the assembly to find one that implements the interface. Or use a factory method. Or use a plugin framework like MEF. Etcetera. — Hans Passant, Jan 31 '13 at 15:47
What exactly does the assembly contain? Type that implements the interface? Or just type that has a method with the same signature? Do you know the name of the type (and possibly the method) you want to use? — svick, Jan 31 '13 at 16:09

score 1 · Accepted Answer · answered Jan 31 '13 at 16:20

Assuming that you don't know the type you want to instantiate in another assembly, you just know it implements IVerifier you can use a method like this:

static TInterface GetImplementation<TInterface>( Assembly assembly)
{
    var types = assembly.GetTypes();
    Type implementationType = types.SingleOrDefault(t => typeof (TInterface).IsAssignableFrom(t) && t.IsClass);


    if (implementationType != null)
    {
        TInterface implementation = (TInterface)Activator.CreateInstance(implementationType);
        return implementation;
    }

    throw new Exception("No Type implements interface.");       
}

Sample use:

using System;
using System.Linq;
using System.Reflection;

namespace ConsoleApplication9
{
    class Program
    {
        static void Main(string[] args)
        {
            IHelloWorld x = GetImplementation<IHelloWorld>(Assembly.GetExecutingAssembly());

            x.SayHello();
            Console.ReadKey();

        }
        static TInterface GetImplementation<TInterface>( Assembly assembly)
        {
            var types = assembly.GetTypes();
            Type implementationType = types.SingleOrDefault(t => typeof (TInterface).IsAssignableFrom(t) && t.IsClass);


            if (implementationType != null)
            {
                TInterface implementation = (TInterface)Activator.CreateInstance(implementationType);
                return implementation;
            }

            throw new Exception("No Type implements interface.");

        }
    }
    interface IHelloWorld
    {
        void SayHello();
    }
    class MyImplementation : IHelloWorld
    {
        public void SayHello()
        {
            Console.WriteLine("Hello world from MyImplementation!");
        }
    }

}

Great answer, wonderful explanation, deserved to be marked as answered and to have a +1 — SVI, Feb 02 '13 at 10:34

Reflection issue

1 Answers1