Show results from multiple async Web Request as downloaded

Question

I am trying to accomplish a task which I am stuck at and need your help on.

I have made an Web Form website in Visual Studio 2015.

I have a BUTTON on a page and a DIV which shows result from web requests.

I am calling GetAsync on three url and making 3 web requests. Lets name them Request1, Request2 and Request3.

Now let's suppose, Request1 takes 1 seconds, Request2 takes 5seconds and Request3 takes 10 seconds to get data.

What happens is that the website completes all async task first and then shows the data.

I want data to be showed as first downloaded first show basis.

private async Task PerformSearchAsync()
    {

        HttpClient client = new HttpClient();
        List<string> urlList = SetUpURLList();

        IEnumerable<Task<RootObject>> downloadTasksQuery =
            from url in urlList select ProcessURL(url, client);

        List<Task<RootObject>> downloadTasks = downloadTasksQuery.ToList();

        while (downloadTasks.Count > 0)
        {
            // Identify the first task that completes.
            Task<RootObject> firstFinishedTask = await Task.WhenAny(downloadTasks);

            // ***Remove the selected task from the list so that you don't
            // process it more than once.
            downloadTasks.Remove(firstFinishedTask);

            // Await the completed task.
            RootObject rootObject = await firstFinishedTask;
            DisplayResult(rootObject);
        }


    }

private void DisplayResult(RootObject rootObject)
    {
        string s = "Name: "+rootObject.name+ " <span><img src =\"http://"+rootObject.logo+"\" alt=\"Source Logo\" style=\"width:16px;height:16px;\"></span>";
        Source.InnerHtml += s;
    }

So what I want to do is if Request1 is completed show its result on web page immediately and then when Request2 or Request3 is completed update the webpage with that request's result

Thank you in advance

With your code first call to the `PerformSearchAsync` will return response only after all downloadTask will be completed. II meant that you create one method which "perform" only one search task. Then call that method from your client (ajax call) separatly with three different parameters — Fabio, Jul 16 '16 at 11:42
@Fabio I do not have much experience with Ajax calls. Cam you point me in right direction with some tutorial or reference? That would be a great help. Thank you. — Raunaq Patel, Jul 16 '16 at 14:40
[http://stackoverflow.com/questions/202538/using-jquery-for-ajax-with-asp-net-webforms](http://stackoverflow.com/questions/202538/using-jquery-for-ajax-with-asp-net-webforms) — Fabio, Jul 16 '16 at 14:46

score 0 · Answer 1 · edited May 23 '17 at 11:58

Task.WhenAny(downloadTasks) run different in windows GUI (WinForm) than WebForm.

In WebForm - ASP.NET knows to keep the request alive until all asynchronous operations for that request have completed.

Async Doesn't Change the HTTP Protocol.

The async operations work in the context of asp.net on the server not in the client(browser), so :

What happens is that the website completes all async task first and then shows the data :) (as you said)

if you enabled Trace, you can get a result like the following (for downloading 5 links) to know what happen:

CategoryMessageFrom First(s)From Last(s) aspx.pageBegin PreInit aspx.pageEnd PreInit0.0001290.000129 aspx.pageBegin Init0.0001430.000014 aspx.pageEnd Init0.0001680.000024 aspx.pageBegin InitComplete0.0001790.000011 aspx.pageEnd InitComplete0.0001910.000012 aspx.pageBegin LoadState0.0002050.000014 aspx.pageEnd LoadState0.0007550.000550 aspx.pageBegin ProcessPostData0.0007720.000017 aspx.pageEnd ProcessPostData0.0012780.000506 aspx.pageBegin PreLoad0.0012950.000017 aspx.pageEnd PreLoad0.0013110.000016 aspx.pageBegin Load0.0013240.000013 aspx.pageEnd Load0.0013530.000029 aspx.pageBegin ProcessPostData Second Try0.0013650.000012 aspx.pageEnd ProcessPostData Second Try0.0013750.000010 aspx.pageBegin Raise ChangedEvents0.0013860.000011 aspx.pageEnd Raise ChangedEvents0.0014000.000014 aspx.pageBegin Raise PostBackEvent0.0014100.000011 aspx.pageEnd Raise PostBackEvent0.0021300.000720 aspx.pageBegin LoadComplete0.0021500.000019 aspx.pageEnd LoadComplete0.0021620.000012 aspx.pageBegin PreRender0.0021730.000011 aspx.pageEnd PreRender0.0021930.000021 http://msdn.microsoft.com0.0301360.027942 http://msdn.microsoft.com/library/windows/apps/br211380.aspx4.5581914.528055 http://msdn.microsoft.com/en-us/library/hh290136.aspx18.06925713.511066 http://msdn.microsoft.com/en-us/library/dd470362.aspx23.2873405.218083 http://msdn.microsoft.com/en-us/library/aa578028.aspx25.5387092.251369 http://msdn.microsoft.com/en-us/library/ms404677.aspx30.5350954.996386 http://msdn.microsoft.com/en-us/library/ff730837.aspx36.9596576.424562 aspx.pageBegin PreRenderComplete41.3143724.354715 aspx.pageEnd PreRenderComplete41.3148800.000508 aspx.pageBegin SaveState41.3152210.000341 aspx.pageEnd SaveState41.3171340.001914 aspx.pageBegin SaveStateComplete41.3171850.000051 aspx.pageEnd SaveStateComplete41.3172100.000025 aspx.pageBegin Render41.3172340.000025 aspx.pageEnd Render41.3193730.002138

So the page will be rendered after Complete execution of all tasks, as you see in the trace result above.

I suggest, as commented by Fabio, use Jquery ajax call separatly with different parameters.

you can read: AsyncTask with a Updatepanel?

Show results from multiple async Web Request as downloaded

1 Answers1