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polling a webservice in .net 4.5

Posted on 2013-11-01
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I am working in vs2012 and .net 4.5.  I have an existing web application that I need to add some functionality to.  Here is one of the things I need to do:  I login to a web service and, once I have logged in, I need to poll the service for "events" on my web page, ie: url = http://thesite/events, which returns a json package.

I have done this in a desktop app using a background worker thread in c# and it works just fine, but I'm not sure how to approach this in a asp.net project.  any direction appreciated.
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Question by:dhenderson12
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Expert Comment

by:Kyle Abrahams
ID: 39616757
You can use an <asp:timer> which is loosley equivalent to a background thread.

Set a timer interval
add the timer_tick  event

in timer_tick
stop the timer
process Web service
update whatever
start the timer.

Timer lives as long as you're on the page.
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Author Comment

by:dhenderson12
ID: 39616824
thx for the response.  the site I'm polling has a timeout value attached (?timeout=60) so that if nothing happens during the 60 seconds, not event is returned and at 60 seconds it will return a response (of course, if something happens within the 60 seconds it will return a response right away).  

so, my action list is:
1. call the site for events
2. async wait for the return
3. read the return and do something
4. call site for events

how could I call the site async with the timer?  I know I sound slow (or dumb) but I'm trying to get my head around this ...
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Accepted Solution

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Kyle Abrahams earned 2000 total points
ID: 39617316
Not slow (or dumb) . . . if you're transitioning to the web from windows it's a different environment so of course you're going to have questions.

What's nice about the timer is that it's already async for you (that is to say, you can still interact with the UI on the main thread).

Think of the timer as a background thread, and then you can invoke the service synchronously.  I hope that makes sense?



Here's some code I previously wrote as an example:  

-  Web Service:

    //taskInfo is a class with a few properties.
     static TaskInfo task = new TaskInfo();

         [WebMethod]
        public TaskInfo GetTask()
        {
            return task;
        }

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-  On the page:
protected void Timer1_Tick(object sender, EventArgs e)
    {

        Timer1.Enabled = false;
         MyWS.MyProjectWSSoap ws = null;
         ws = Session["Myservice"] as MyWS.MyProjectWSSoap ;
        Panel.Visible = true;

       MyWS.MyProjectWSSoap.TaskInfo ti =  ws.GetTask();


        if (Overall_Progress.Value !=  ti.overall_progress)
            Overall_Progress.Value =  ti.overall_progress;

        if (Current_Progress.Value != ti.current_progress)
            Current_Progress.Value =  ti.current_progress;

        lblCurrentStep.Text = ti.step_name;
        
        lblRefresh.Text = "Last Refresh: " + System.DateTime.Now.ToString("MM/dd/yyyy hh:mm:ss");

        
        //The process has finished.  Cleanup
        if (Session["dw_ProcessComplete"]  != null && (bool)Session["dw_ProcessComplete"] == true)
        {
          //I had to add another timer_tick to push a file down . . . you most likely not need this but I left it to show you it can be done.
            Timer2.Enabled = true;         
        }

        if (Session["dw_ErrorMessage"] != null)
        {
            lblError.Text = Session["dw_ErrorMessage"].ToString();
            pnlError.Update();
        }
        if (string.IsNullOrEmpty(lblError.Text) && !(Session["dw_ProcessComplete"]  != null && (bool)Session["dw_ProcessComplete"] == true))
            Timer1.Enabled = true;
    }

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Feel free to ask more questions.
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Author Closing Comment

by:dhenderson12
ID: 39617621
beautiful!  thanks for the help.
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