c# - Progress report using SignalR and IProgress interface

Question

I have a Hub class, which has a long running method, I need to display a progress bar while it's working.

I read this article and I think it is possible to use IProgress interface in async methods to send long running operation status.

I write a method like this:

    public async Task<string> GetServerTime(IProgress<int> prog)
    {
        await Task.Run(() => {
            for (int i = 0; i < 10; i++)
            {
                prog.Report(i * 10);
                System.Threading.Thread.Sleep(200);
            }
        });

        return DateTime.Now.ToString();
    }

And I try to invoke the method like this:

 var appHub = $.connection.appHub;
 $.connection.hub.start();
 appHub.server.getServerTime()
              .done(function (time) {
                    alert(time);
               });

But I don't know how can I get the progress reports.

Answer 1

You can use progress, as such:

var appHub = $.connection.appHub;
$.connection.hub.start().done(function() {
  appHub.server.getServerTime()
    .progress(function (update) { alert(update); })
    .done(function (time) { alert(time); });
});

On a side note, there's no point in using Task.Run over CPU-bound code on the server side. Your server-side code could just as easily be:

public string GetServerTime(IProgress<int> prog)
{
    for (int i = 0; i < 10; i++)
    {
        prog.Report(i * 10);
        System.Threading.Thread.Sleep(200);
    }

    return DateTime.Now.ToString();
}

Your server-side methods should only be async if they have true asynchronous work to do (usually I/O-bound operations). As a general rule, avoid Task.Run on the server side.