C#

An article like the one you posted that is geared to VB6 COM DLLs, rather than C++ COM DLLs is what I am looking for.

DaveyM69 wrote:

Have I got this right?
TCPConnection knows about FramingEngine.
FramingEngine knows about MessagingEngine.

DaveyM69 wrote:

If so,
TCPConnection could call a method in FramingEngine.
FramingEngine could call a method in MessagingEngine.

Dewald wrote:

So, I decided to employ this mechanism of events being raised and handled to pass the message up the chain of abstraction again. As I said, it works, but I'm not sure this is good programming. What are your opinions?

interface IFrameEngine
{
   event MessageReceived;
   void SendMessage(...);    
}

S. Senthil Kumar wrote:

The event mechanism looks ok for the receiving part, but it looks a bit awkard for the sending part.

S. Senthil Kumar wrote:

Usually, people think of events as things that are optional i.e., you can subscribe if you're interested. People also implicitly associate it with multiple listeners.

S. Senthil Kumar wrote:

But sending the message is different - you don't want to have a SendMessage event with zero subscribers, do you?

S. Senthil Kumar wrote:

Do you anticipate multiple subscribers sending messages?

S. Senthil Kumar wrote:

OTOH, I think of an interface, like

interface IFrameEngine
{
event MessageReceived;
void SendMessage(...);
}


and have message engine hold a reference to this interface. The dependencies are only one way i.e., MessageEngine depends on IFrameEngine.

Dewald wrote:

Would you mind elaborating a bit?

interface IFrameEngine
{
event MessageReceived;
void SendMessage(...);
}

class DefaultFrameEngine : IFrameEngine
{
   public event MessageReceived;

   public void SendMesssage(...) {...}

   protected void RaiseMessageReceived(...) {...}
}

class MessageEngine
{
   IFrameEngine frameEngine;

   internal MessageEngine(IFrameEngine frameEngine)
   {
       this.frameEngine = frameEngine;
       this.frameEngine.MessageReceived += ....(HandleMessageReceived)
   }

   internal void HandleMessageReceived(...)
   {
     if (mustSendMesssage)
       frameEngine.SendMessage(...);
   }
}