Grammar issue with respect to anonymous functiosn

Question

From m$ site. I don't get the += o,a what is that ???

private void GetResponse(Uri uri, Action<Response> callback)
{
    WebClient wc = new WebClient();

    wc.OpenReadCompleted += (o, a) =>
    {
        if (callback != null)
        {
            DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(Response));
            callback(ser.ReadObject(a.Result) as Response);
        }
    };
    wc.OpenReadAsync(uri);
}

I suggest you read up on delegates, events, and lambda expressions and that should just about cover it. — juharr, Aug 02 '17 at 19:34
Possible duplicate of [Understanding events and event handlers in C#](https://stackoverflow.com/questions/803242/understanding-events-and-event-handlers-in-c-sharp) — Andrew Sun, Aug 02 '17 at 20:12

score 1 · Answer 1 · answered Aug 02 '17 at 19:27

1

wc.OpenReadCompleted += (o, a) => { }

This is assigning an anonymous delegate to the wc.OpenReadCompleted event. The (o,a) part are the method parameters.

o is object. a is the EventArgs

answered Aug 02 '17 at 19:27

Stuart

3,949
7
29
58

Pavel Aschepkov · Answer 2 · 2017-08-02T19:33:14.393

0

As I can see from the signature of OpenReadCompletedEventHandler (which should be used to subscribe to OpenReadCompleted event), o is a sender and a is an instance of OpenReadCompletedEventArgs.

In general this approach of subscription to events is basically instantiating a delegate using a lambda expression, one can do this since C# 3.0.

edited Aug 02 '17 at 19:33

answered Aug 02 '17 at 19:24

Pavel Aschepkov

81
4

But where is the o used/consumed? – JAMES Aug 02 '17 at 22:56

Grammar issue with respect to anonymous functiosn

2 Answers2