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Using the .Net AJAX Update Panel - VB.Net
Language(s):VB.Net
Category(s):AJAX, ASP.Net
This article will show how to use the .Net AJAX Update Panel control to provide feedback and prevent timeout of long running processes. This article will simulate a long running process and show how we can give feedback to the user during the processing. This project was written using Visual Studio 2008 using VB.Net.

See also: Using the .Net AJAX Update Panel – C#

This article will show how to use the .Net AJAX Update Panel control to provide feedback and prevent timeout of long running processes. This article will simulate a long running process and show how we can give feedback to the user during the processing. This project was written using Visual Studio 2008 using VB.Net.

What is the AJAX Update Panel Control?

AJAX (Asynchronous JavaScript and XML) is a short acronym for a long name but a very simple concept. AJAX is simply a way of updating a portion of a web page without refreshing the entire page. Anyone who has used google lately has used an AJAX application called google suggest, which provides a dropdown of suggestions as you enter a search string. (See Figure 1).   



Figure 1 – Google Suggest in action.

If you compare pressing the Refresh button with the time it takes for google suggest to react to your key strokes, you will see the great advantage in performance over reloading the entire page.

The .Net Update Panel provides a very simple control that lets us take advantage of this basic concept without the need to use javascript or jQuery.

Creating the Web Application

To get started with this project, start Visual Studio and create a new Web Site from the menu. You will want to initially lay out the page to look something like Figure 2.

short acronym for a long name but a very simple concept. AJAX is simply a way of updating a portion of a web page without refreshing the entire page. Anyone who has used google lately has used an AJAX application called google suggest, which provides a dropdown of suggestions as you enter a search string. (See Figure 1).   

Figure 2 – AJAX Update Panel screenshot

I have also added a label at the bottom of the form with an id of “lblStatus” that will display the status as the long running process does its work. I have named the button and attached two events – one that will run on the client side to initially set the label text, and a server side method that will simulate the long running process. The HTML snippet for the button looks like this:

    <asp:Button ID="btnLongProcess" runat="server"

        Text="Long Running Process"

        onclick="btnLongProcess_Click"

        onclientclick="btnLongProcess_onclientclick()"/>

The javascript function is declared in the <head> tag and should look something like this:

    <script type="text/javascript" language="javascript">

        function btnLongProcess_onclientclick() {

            document.getElementById("lblStatus").innerText = "Processing...";

            return (true);

        }

    </script>

You can now double-click the button to bring up the code window and write the method that will simulate the long running process, which looks like the following:

    Private Const STATUS_COMPLETE = "Process Complete:"

    Private Shared _status As String

    Protected Sub btnLongProcess_Click(ByVal sender As Object, _

                                    ByVal e As System.EventArgs) _

                                        Handles btnLongProcess.Click

        Dim i As Integer

        'Simulate a long running process

        For i = 1 To 100

            _status = "Processing item: " + i.ToString()

            System.Threading.Thread.Sleep(1000)

        Next

        _status = STATUS_COMPLETE

    End Sub

Be sure to declare the _status string outside the method and declared as static. We will be using this string to send status back to the AJAX UpdatePanel control.

AJAX Extension Controls

Now let’s look at adding the AJAX Extension controls. These are found in the AJAX Extensions section of the Toolbox. To use any of these controls, you will need to place a ScriptManager control on the form. For this application, we will also add an UpdatePanel, and Timer control. Within the UpdatePanel control we need a ContentTemplate tag. The Timer and Label controls are placed inside the ContentTempate tags as shown below:

    <asp:UpdatePanel ID="UpdatePanel1" runat="server"

         UpdateMode="Conditional">

      <ContentTemplate>

        <asp:Label ID="lblStatus" runat="server" Text=""></asp:Label>

        <asp:Timer ID="Timer1" runat="server" Interval="5000"

            ontick="Timer1_Tick" />

      </ContentTemplate>

    </asp:UpdatePanel>

 Figure 3 shows a screenshot of the AJAX Extensions tools and the form: 


Figure 3 – AJAX Extensions

Now let’s add the last method – Timer_Tick. Double-click the Timer control to bring up the code window and add the following method:

    Protected Sub Timer1_Tick(ByVal sender As Object, _

                              ByVal e As System.EventArgs) _

                                Handles Timer1.Tick

        lblStatus.Text = _status

    End Sub

This method will wake up every 5 seconds = 5000 milliseconds as defined in the Interval attribute in the Timer tag. When it does, it will set the Label, (which must lie within the UpdatePanel tag) to the current status as updated by the long running process.

Check it out

Now when you run the application, pressing the Long Running Process button should cause the Label to initially display “Processing…” followed by ½ second or so updates of the current line number being processed. If you have any problems, you can download the code from the link above. 

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