CODEWITHSUNDEEP
c#events
Lasse Christiansen
Lasse Christiansen

Reputation: 10325

Is it possible to subscribe to event subscriptions in C#?

If I have an event like this:

public delegate void MyEventHandler(object sender, EventArgs e);
public event MyEventHandler MyEvent;

And adds an eventhandler like this:

MyEvent += MyEventHandlerMethod;

... is it then possible to register this somehow? In other words - is it possible to have something like:

MyEvent.OnSubscribe += MySubscriptionHandler;

Upvotes: 6

Views: 235

Answers (5)

Tigran
Tigran

Reputation: 62265

It's possible if you declare your custom event, like this pseudocode: 

class MyClass
{


    public event EventHandler MyEvent
    {
        add    {     //someone subscribed to this event  ! }
        remove {     //someone unsubscribed from this event ! }
    }


    ...
}

Upvotes: 1

Cinchoo
Cinchoo

Reputation: 6326

I guess, you are looking for event accessors. Way to customizing the references to the subscribers. Here is how you can do it

public class TestClass
{

   private event EventHandler UnderlyingEvent;
   public event EventHandler TestEvent
   {
        add
        {
             UnderlyingEvent += value;
        }
        remove
        {
             UnderlyingEvent -= value;
        }
   }
}

For more information, please visit this article

http://msdn.microsoft.com/en-us/magazine/cc163533.aspx

Upvotes: 1

Tim
Tim

Reputation: 15247

When you define your events, you can actually use the longer format to execute more code when people attach or remove themselves from your events.

Check out the info on the add and remove keywords.

Upvotes: 1

dtb
dtb

Reputation: 217411

Similar to auto-implemented properties, events are auto-implemented by default as well.

You can expand the declaration of an event as follows:

public event MyEventHandler MyEvent
{
    add
    {
        ...
    }
    remove
    {
        ...
    }
}

See, for example, How to: Use a Dictionary to Store Event Instances (C# Programming Guide)

See Events get a little overhaul in C# 4, Part I: Locks for how auto-implemented events differ between C# 3 and C# 4.

Upvotes: 11

kfuglsang
kfuglsang

Reputation: 2505

It is possible to declare the event accessors specifically, i.e., the add and remove accessors.

Doing so makes it possible to do custom logic when new event handlers are added.

Upvotes: 6

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