Multiple Async Operations with Delegates

Question

Code:

private delegate void NotificationDelegate(sis_company company, int days, string type, string param);

private NotificationDelegate _notDel;

private void Notifications(sys_company company, int days, string type, string param)
{
    if (*something*)
    {
        _notDel = SendEmails;
        _notDel.BeginInvoke(company, days, type, param, CallBackNotification, null);
    }
}

private void SendEmails(sys_company company, int days, string type, string param)
{
    //Here I'll send all e-mails.
}

private void CallBackNotification(IAsyncResult r)
{
    if (this.IsDisposed) return;

    try
    {
        _notDel.EndInvoke(r);
    }
    catch (Exception ex)
    {
        LogWriter.Log(ex, "EndInvoke Error");
    }
}

Expected Behaviour:

The Notifications method is called whenever a company meets the deadline. During the initialization a method loops for each company and calls Notifications inside that loop.

Problem:

As you can see, _notDel is a global variable, used later on to EndInvoke the delegate. The problem is that after the second Notifications call, the object is not the same anymore, giving me the error that says:

"The IAsyncResult object provided does not match this delegate."

Why is _notDel global? Can you make it per instance? You have to encapsulate each delegate instance for this to work — Yuval Itzchakov
– Yuval Itzchakov, Commented Feb 2, 2015 at 12:33
You simply need a transient object which holds the delegate as a field which is passed as a state parameter for later use. — Sriram Sakthivel
– Sriram Sakthivel, Commented Feb 2, 2015 at 12:34
@YuvalItzchakov How can I EndInvoke inside the CallBackNotification? — Nicke Manarin
– Nicke Manarin, Commented Feb 2, 2015 at 12:34
Just pass your _notDel as the last parameter for BeginInvoke and use r.AsyncState to get the source delegate then — Alex K.
– Alex K., Commented Feb 2, 2015 at 12:36

Nicke Manarin · Accepted Answer · 2015-02-02 13:04:01Z

1

Just pass your notDel as the last parameter for BeginInvoke and use r.AsyncState to get the source delegate then.

//Call like this:

NotificationDelegate notDel = Notifications;
notDel.BeginInvoke(company, days, type, param, CallBackNotification, notDel);

//And inside the CallBack:

var del = r.AsyncState as NotificationDelegate;

if (del != null)
    del.EndInvoke(r);

edited Feb 2, 2015 at 13:04

Nicke Manarin

3,4805 gold badges48 silver badges97 bronze badges

answered Feb 2, 2015 at 12:44

Alex K.

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