C # method overload

Question

I am new to C # and trying to figure out how I can easily implement the following:

I have a subscriber:

public interface ISubscriber
{
    void HandleMessage(IMessage message);
}

class TriggerSubscriber : ISubscriber
{
    public void HandleMessage(IMessage message)
    {
         //This will be called by default   
    }
    public void HandleMessage(TriggerMessage message)
    {
         //This won't work, why?    
    }
}

Attempted to process the following message:

public class TriggerMessage : IMessage
{
    string identifier { get; set; }

    public TriggerMessage(string triggerIdentifier)
    {
        identifier = triggerIdentifier;
    }
}

public interface IMessage
{

}

I expected the following to be triggered:

public void HandleMessage(TriggerMessage message)

instead

public void HandleMessage(IMessage message)

from

ISubscriber trigger = new TriggerSUbscriber();
trigger.HandleMessage(
    new TriggerMessage()
);

Am I missing something?

Answer 1

Your variable is triggerdefined as having a type ISubscriber(regardless of the type of the actual object). ISubscriberonly has one method signature:

void HandleMessage(IMessage message);

Thus, the compiler calls this method.

In fact, if you did this:

class TriggerSubscriber : ISubscriber
{
  public void HandleMessage(IMessage message)
  {
  }
  public void HandleMessage(int something)
  {
  }
}

And then try to do this:

ISubscriber trigger = new TriggerSubscriber();
trigger.HandleMessage(4);

The compiler will complain about the lack of such a method in ISubscriber, which takes a parameter int.

There are three options:

• TriggerMessage

• trigger TriggerSubscriber, ISubscriber, TriggerSubscriber HandleMessage:

  ((TriggerSubscriber)trigger).HandleMessage(new TriggerMessage());
  

• :

  class TriggerSubscriber : ISubscriber
  {
      public void HandleMessage(IMessage message)
      {
        var triggerMessage = message as TriggerMessage;
        if(triggerMessage != null)
        {
           // Casting is not necessary, but I'd still put it
           // here just to make it clear
           HandleMessage((TriggerMessage)triggerMessage);
           return;
        }
        // other code
      }
      public void HandleMessage(TriggerMessage message)
      {
      }
  }
  

# 3 ( , TriggerMessage HandleTriggerMessage ),

Answer 2

, trigger ISubscriber, HandleMessage , :

void HandleMessage(IMessage message)

, , . .

ISubscriber trigger TriggerSubscriber trigger ( !), , .