Refreshing data using AJAX in ASP masterpage - asp.net

Question

I have some processes that run as a background job, allowing a user to continue to use a page, when the jobs are finished (which can take a few minutes) i want to display a message to the user, the best place to display this would be the masterpage AFAIK (incase they move from page to page on the site) so i have defined a div in the masterpage file.
I am trying to find the best method for displaying the data, at the moment i have a method in the masterpage vb file which polls a database to see if the job(which involves complex logic and some db access) has completed, if it has, it shows a message in the div e.g. "Job 13132 has completed" - which works fine.
The problem is this is not dynamic, and i have to refresh the page to call the function that checks if the processes have finished, how can i use AJAX to deliver this content automatically every 5 seconds?
I have tried using an asp timer with a 5 second tick time but the entire page refreshes on the timer click event every 5 seconds.
Protected Sub Timer1_Tick(Byval sender as Object, Byval e As EventArgs)
poll_results()
End Sub
Public Sub poll_results()
'database access logic
If dbtable.isCompleted = True
Dim sb As New StringBuilder()
sb.Append("$('#status').html('Job abc123 is complete');")
Page.ClientScript.RegisterStartupScript(GetType(Page), "myscript", sb.ToString(), True)
End If
End Sub
Is there a way to only refresh the div with the updated message, without a full refresh happening using this code? Or if this is not possible, is there any way to replicate the above function using jQuery and still be able to update the DIV text only if a job as finished?

Answer 1

You can easily go throw what we called, an async call, instead calling your method in the same page, just create an async folder in your website and add a new Generic Handler, call the page, for example checkPendingJobs.ashx.
in that page, add your current method:
Public Sub ProcessRequest (Byval context as HttpContext)
Dim r As String = ""
If dbtable.isCompleted = True
Dim sb As New StringBuilder()
r = "Job abc123 is complete"
End If
context.Response.ContentType = "text/plain"
context.Response.Write(r)
}
Now that you did your Server part, let's do the client part, in your page, add this jQuery code to tour masterpage, witch will fire every time some one refreshes the page, or you can use setInterval() to check it every xx seconds:
<script>
var checkJobs = true;
$(document).ready(function() {
// every time someone refreshes the page
checkPendingJobs();
// every 5 seconds...
setInterval(function(){ checkPendingJobs(); }, 5000);
});
function checkPendingJobs() {
// no need to check it if we already have a valid response
if(!checkJobs) return;
// caching issue trick
var now = new Date();
$.ajax({
url: "../async/checkPendingJobs.ashx",
type: "GET",
data: { t: now.getTime() },
success: function(data) {
// do we have text to show?
if(data.length > 0) {
alert(data);
checkJobs = false; // no need to check it more...
// $('#status').html(data);
}
},
error: function(msg) {
alert('Error found:\n' + msg);
}
});
}
</script>

Answer 2

The most common approach to this would be to create a single page that will render out either JSON or HTML. This of this as the "poll_results" method, think of it as poll_result.aspx. You can either pass a single Job ID to this page or just do a poll for any jobs that have finished since the last polling.
Your Masterpage will have a snipet of JavaScript that will use a timer (client side javascript timer) to send an AJAX request to the server, hitting your "poll_request.aspx" page. This page will return either HTML or JSON and you will write some JavaScript to show your message. If you need some code samples let me know.