How to call an explicitly implemented interface-method on the base class

Question

I have a situation, where two classes (one deriving from the other) both implement the same interface explicitly:

interface I
{
  int M();
}

class A : I
{
          


        

Answer 1

It is possible using reflection.
The code follows. I added caching as a basic optimization, but it can be optimized further by using Delegate.CreateDelegate on methodInfo. Also, parameter count and type checks can be added using methodInfo.GetParameters().

interface I   
{   
    int M();   
} 

class A : I   
{   
    int I.M() { return 1; }   
} 

class B : A, I   
{   
    BaseClassExplicitInterfaceInvoker<B> invoker = new BaseClassExplicitInterfaceInvoker<B>();
    int I.M() { return invoker.Invoke<int>(this, "M") + 2; }   
}

public class BaseClassExplicitInterfaceInvoker<T>
{
    private Dictionary<string, MethodInfo> cache = new Dictionary<string, MethodInfo>();
    private Type baseType = typeof(T).BaseType;

    private MethodInfo FindMethod(string methodName)
    {
        MethodInfo method = null;
        if (!cache.TryGetValue(methodName, out method))
        {
            var methods = baseType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);

            foreach (var methodInfo in methods)
            {
                if (methodInfo.IsFinal && methodInfo.IsPrivate) //explicit interface implementation
                {
                    if (methodInfo.Name == methodName || methodInfo.Name.EndsWith("." + methodName))
                    {
                        method = methodInfo;
                        break;
                    }
                }
            }   

            cache.Add(methodName, method);
        }

        return method;
    }

    public RT Invoke<RT>(T obj, string methodName)
    {            
        MethodInfo method = FindMethod(methodName);
        return (RT)method.Invoke(obj, null);
    }

}   //public static class BaseClassExplicitInterfaceInvoker<T>

Here is the source of my inspiration.

Answer 2

Unfortunately, it isn't possible.
Not even with a helper method. The helper method has the same problems as your second attempt: this is of type B, even in the base class and will call the implementation of M in B:

interface I
{
  int M();
}
class A : I
{
  int I.M() { return 1; }
  protected int CallM() { return (this as I).M(); }
}
class B : A, I
{
  int I.M() { return CallM(); }
}

The only workaround would be a helper method in A that is used in A's implementation of M:

interface I
{
  int M();
}
class A : I
{
  int I.M() { return CallM(); }
  protected int CallM() { return 1; }
}
class B : A, I
{
  int I.M() { return CallM(); }
}

But you would need to provide a method like this also for B if there will be a class C : B, I...

Answer 3

using System;

namespace SampleTest
{
    interface IInterface1
    {
        void Run();
    }

    interface IInterface2
    {
        void Run();
    }

    public class BaseClass : IInterface1, IInterface2
    {
        public void Interface1Run()
        {
            (this as IInterface1).Run();
        }

        public void Interface2Run()
        {
            (this as IInterface2).Run();
        }

        void IInterface2.Run()
        {
            Console.WriteLine("I am from interface 2");
        }

        void IInterface1.Run()
        {
            Console.WriteLine("I am from interface 1");
        }
    }

    public class ChildClass : BaseClass
    {
        public void ChildClassMethod()
        {
            Interface1Run();
            Interface2Run();      
        }
    }
    public class Program : ChildClass
    {
        static void Main(string[] args)
        {
            ChildClass childclass = new ChildClass();
            childclass.ChildClassMethod();
        }
    }
}

Answer 4

Here is my version of Roland Pihlakas's nice solution. This version supports the entire inheritance chain instead of immediate base class. The Invoke method includes additional parameters and there is a void type Invoke for non-function methods.

public class BaseClassExplicitInterfaceInvoker<T>
{
    readonly Dictionary<string, MethodInfo> Cache = new Dictionary<string, MethodInfo>();

    MethodInfo FindMethod(string MethodName)
    {
        if (Cache.TryGetValue(MethodName, out var Result)) return Result;

        var BaseType = typeof(T);
        while (Result == null)
        {
            if ((BaseType = BaseType.BaseType) == typeof(object)) break;

            var Methods = BaseType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);
            Result = Methods.FirstOrDefault(X => X.IsFinal && X.IsPrivate && (X.Name == MethodName || X.Name.EndsWith("." + MethodName)));
        }

        if (Result != null) Cache.Add(MethodName, Result);

        return Result;
    }

    public void Invoke(T Object, string MethodName, params object[] Parameters) => FindMethod(MethodName).Invoke(Object, Parameters);
    public ReturnType Invoke<ReturnType>(T Object, string MethodName, params object[] Parameters) => (ReturnType)FindMethod(MethodName).Invoke(Object, Parameters);
}

Answer 5

On option would be to create a base class that doesn't excplicitly implement an interface, and to only implement the interface on the subclass.

public class MyBase
{
    public void MethodA()
    {
        //Do things
    }
}

public interface IMyInterface
{
    void MethodA();
    void MethodB();
}


public class MySub: MyBase, IMyInterface
{
    public void MethodB()
    {
        //Do things
    }
}

Doing this will allow you to access the base classes MethodA without having to implemnet it in MySyb.

Answer 6

it is necessary explicitly?... Can you use an abstract class or class instead of interface?

interface ISample {}
class A : ISample {}
class B : A {}
...
base.fun();
...

http://msdn.microsoft.com/en-us/library/hfw7t1ce(v=vs.71).aspx

I have no idea its not possible call base method when it comes from implementation of interface.