How to do I return an item from a custom event handler

Question

A project I'm working on requires me to be able to fire off an event everytime an item is added to a list. To achieve this, I created a custom List class inheriting from List and added a OnAdd event. I also want to return the item being added as EventArgs for which I added some more code (given below):

    public class ClientListObservable<Client>:List<Client>
    {
        public event EventHandler<EventArgs<Client>> OnAdd;

        public void Add(Client item)
        {
            if (null != OnAdd)
            {
                OnAdd(this, new EventArgs<Client>(item));
            }

            base.Add(item);
        }
    }

    public class EventArgs<Client> : EventArgs
    {
        public EventArgs(Client value)
        {
            m_value = value;
        }

        private Client m_value;

        public Client Value
        {
            get { return m_value; }
        }
    }

This is how I add a handler

clientList.OnAdd += new EventHandler<EventArgs<Client>>(clientList_OnAdd);

But, in the OnAdd method:

private void clientList_OnAdd(object sender, EventArgs e)
        {
            //want to be able to access the data members of the Client object added
        }

I can only access e.Equals, e.GetHashCode, e.GetType and e.ToString, and none of the members of Client class.

score 6 · Accepted Answer · answered Feb 09 '11 at 19:43

6

Change your event args to:

public class ClientEventArgs : EventArgs
{
    public ClientEventArgs(Client value)
    {
        m_value = value;
    }

    private Client m_value;

    public Client Value
    {
        get { return m_value; }
    }
}

Then:

    private void clientList_OnAdd(object sender, ClientEventArgs e)
    {
        Client client = e.Value;
    }

answered Feb 09 '11 at 19:43

Reed Copsey

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Thanks. This is definitely cleaner than what I was implementing. – Ayush Feb 09 '11 at 19:53

score 3 · Answer 2 · answered Feb 09 '11 at 19:42

3

Shouldn't your event handler be declared like this:

private void clientList_OnAdd(object sender, EventArgs<Client> e)

?

answered Feb 09 '11 at 19:42

Kirk Woll

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The class declaration won't work, either, there... It's not `EventHandler` here. There is no `EventArgs`. See: http://stackoverflow.com/questions/3312134/does-net-have-a-built-in-eventargst – Reed Copsey Feb 09 '11 at 19:44
@Reed, I know -- I had assumed the OP had written that variant himself (which his code shows he did.) – Kirk Woll Feb 09 '11 at 20:31

score 1 · Answer 3 · answered Feb 09 '11 at 19:42

1

you should derive your custom class from EventArgs and have a member to host your custom objects in there, then you should invoke the event passing such specialized EventArgs which you would have created and initialized as needed.

answered Feb 09 '11 at 19:42

Davide Piras

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score 1 · Answer 4 · answered Feb 09 '11 at 19:44

1

Create your own event args that extends EventArgs and has a public property of a "Client" object. Then on add populate the custom EventArgs with the new item and return it.

answered Feb 09 '11 at 19:44

William

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How to do I return an item from a custom event handler

4 Answers4