CODEWITHSUNDEEP
c#eventsdelegates
nan
nan

Reputation: 585

How to raise the same event from different classes?

I have a class library that has a number of classes. Any of these classes should be able to send a message (string) to the client at any point of time . I want to have a Generic Event that can be raised from a number of classes. I don't want a separate event for each class.

Something like this:

public class GenericEvent
{
    // Here I have an event.   
}

public class LibClass1
{
    //Raise event here.
}

public class LibClass2
{
    //Raise event here
}

public class Client
{
  //Subscribe to the event here
}

Is this the right approach? If yes, how can it be achieved? The examples I looked up all have a separate event for each class.

Upvotes: 3

Views: 517

Answers (4)

Pavan Chandaka
Pavan Chandaka

Reputation: 12751

I have another approach.

Derive all of your classes from one single base class. (of course any library do that, .net or MFC or Qt or java framework).

you have a single event "event 1" in base class. In that event1 handler, raise "event 2".

Subscribe all your child classes to the "event2" of parent class and handle your business in respective child classes.

Upvotes: 0

Martin S.
Martin S.

Reputation: 142

I would work with inheritance. For example:

public class ParentClass : Form
{
    public ParentClass() {
        this.FormClosed += sendString;
    }

    private void sendString(object sender, FormClosedEventArgs e)
    {
        throw new NotImplementedException();
    }
}

public class GenericEvent : ParentClass { }
public class LibClass1 : ParentClass { }
public class LibClass2 : ParentClass { }
public class Client : ParentClass { }

Now all of you Clases have the event of the ParentClass.

Upvotes: 1

mybirthname
mybirthname

Reputation: 18127

    public class MyEventArgs : EventArgs
    {
        // class members
    }

    public abstract class Lib
    {
        public event EventHandler ShapeChanged;

        public virtual void OnShapeChanged(MyEventArgs e)
        {
            if (ShapeChanged != null)
            {
                ShapeChanged(this, e);
            }
        }
    }

    public class LibClass1 : Lib
    {
        //Raise event here.
    }

    public class LibClass2 : Lib
    {
        //Raise event here
    }

    static void Main(string[] args)
    {
        LibClass1 lib1 = new LibClass1();
        LibClass2 lib2 = new LibClass2();

        lib1.ShapeChanged += Lib1_ShapeChanged;
        lib2.ShapeChanged += Lib1_ShapeChanged;

        lib1.OnShapeChanged(new MyEventArgs());

    }

Here full example create an abstract class in which you have the event.

Upvotes: 1

Dennis
Dennis

Reputation: 37770

It depends on what this event is and use cases, but one of the options is to use inheritance:

public class GenericEvent
{
    // Here I have an event.
    protected void RaiseEvent();
}

public class LibClass1 : GenericEvent 
{
    public voidDoSomethingAndRaiseEvent()
    {
        // ...
        RaiseEvent();
    }
}

This is how INotifiPropertyChanged is usually implemented.

If inheritance is impossible and you're using aggregation, LibClass1 and LibClass2 should act as some facade/decorator for GenericEvent: they must have their own event, which re-directs calls to GenericEvent's event and method(-s) to raise it:

public class GenericEvent
{
    public event EventHandler SomeEvent;
    // ...
}

public class LibClass1
{
    private readonly GenericEvent _ge;

    // ...

    public event EventHandler SomeEvent
    {
        add { _ge.SomeEvent += value; }
        remove { _ge.SomeEvent -= value; }
    }

    public void DoSomethingAndRaiseEvent()
    {
        // ...
        SomeEvent?.Invoke(this, EventArgs.Emtpy);
    }
}

Upvotes: 3

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