Question

I am sending several messages over a websocket inside of a callback. The problem is, that if one sending is not completed and another one is started the function exceeds with an exception. Due to socket.SendAsync() is async I could wait for it with await. As soon as I am using await I will have to declare my lambda expression as async. But as soon as I do this the callback is never called. Does anyone know why or do have a solution/workaround for this?

Example code:

queue.QueueCompleted += async (s, eA) =>
    {
        z = dr.Start + 1;
        while (z < (dr.Start + 1 + dr.Limit))
        {
            string path = AppDomain.CurrentDomain.BaseDirectory + @"DCM\" + dr.Code.Replace('.', '_') + @"\IMAGE" + z.ToString() + ".jpg";
            Image image = null;
            image = Image.FromFile(path);
            ImageConverter ic = new ImageConverter();
            byte[] buffer = (byte[])ic.ConvertTo(image, typeof(byte[]));
            try
            {
                if (socket != null && socket.State == WebSocketState.Open)
                {
                    Debug.WriteLine("REACHED");
                    await socket.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Binary, true, CancellationToken.None);
                    image.Dispose();
                }
            }
            catch (Exception e)
            {
                image.Dispose();
                break;
            }
            z++;
        }
    };

The callback is a simple EventHandler and is called like if(QueueCompleted != null) QueueCompleted(e, null);

Answer 1

Probably not the most efficient, but here’s a pattern I use for inline async code:

queue.QueueCompleted += (s, eA) =>
            {
                Task.Run(async ()=>{
                    //blah
                });
            };