Where to insert an EventHandler in factory pattern

I'm quiet new in design pattern and I have a question about the abstract factory pattern. I'm trying to build a connection with a database that receives data through the network, but I have a problem with the design of this architecture. I need to attach an event to this element in order to receive the state changing, but I don't know how to draw the class diagram.

I have the main abstract class:

 public abstract class NetItem
{

    public abstract void Connect();
    public abstract void Disconnect();
    public abstract void Close();

    // THIS SHOULDN'T BE HERE
    public abstract void AttachConnectionStateChanged(IConnectionStateChanged state);

    // other methods

}


 public interface IConnectionStateChanged
{
    void StateChangedEvent(object sender, MtConnectionEventArgs e);

} 

As you can see in IConnectionStateChanged the eventargs is MtConnectionEventArgs, but I know it's the wrong place for this specialization in the abstract class.
I know I can handle this problem in the concrete class, something like this:

public class MtApiNetItem : NetItem
{
    MtApiClient mtApi = null;
    private MtApiParamsFactory mtApiParamsFactory;

    // Code for handling statechanged
}

But in the main program I would like to write something like this:

MtApiFactory factory = new MtApiFactory()
NetItem myItem = factory.CreateConnection(params...);

because I want to follow the DiP rule:
"Depend on abstractions. Do not depend on concrete classes"

How can I write my diagram class to subscribe to the StateChange event without personalizing the main abstract class?

Could you give me an advice how to manage this problem?

Thank you