The Disturbed Buddha

Simple Observations of a Self-proclaimed Novice

Wrapping ASP.NET AJAX TabContainer Tabs

Check out Nazar Rizvi’s article on how to get your tab headers to wrap onto a second row for your ASP.NET AJAX TabContainer control.  Common problem; easy fix.

http://www.narizvi.com/blog/post/Two-rows-of-tab-headers-in-TabContainer-in-Ajax-Control-Toolkit.aspx

December 19, 2007 Posted by | Ajax, ASP.NET, Web Development | 2 Comments

Handling Multiple Asynchronous Postbacks

Sometimes multiple asynchronous postbacks get triggered. Now, I’m not talking about situations where we want to disable a submit button, so that the user doesn’t click it fifty times waiting for something to happen. Instead, I’m referring to situations where we do want each postback to happen in the order it was fired.

However, when a page makes multiple asynchronous postbacks at the same time, the default action is that the PageRequestManager gives the most recent postback precedence. This cancels any prior asynchronous postback requests that have not yet been processed. (Get further explanation.)

So, let’s create a way to “queue up” our asynchronous postback requests and fire them off in order, one by one. First, let’s create an aspx page with three buttons inside of an UpdatePanel:

<asp:ScriptManager ID="ScriptManager1" runat="server" /> 
<asp:UpdatePanel ID="UpdatePanel1" runat="server"> 
    <ContentTemplate> 
        <asp:Button ID="Button1" runat="server" Text="Button" /> 
        <asp:Button ID="Button2" runat="server" Text="Button" /> 
        <asp:Button ID="Button3" runat="server" Text="Button" /> 
    </ContentTemplate> 
</asp:UpdatePanel>

There is no need to wire up any click events in the code-behind for our sample. While you could, all that we are concerned about is that they each cause a postback.

Next, let’s add some deliberate latency into the code so that our postback requests can pile up. Every postback to the server will now take 3 ½ seconds, so that is the fastest each request can be processed.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 
  System.Threading.Thread.Sleep(3500) 
End Sub

Now, let’s look at the JavaScript code that will manage the backed-up postback requests for us. Add this script block after the ScriptManager on the page but before the closing </html> tag.

<script type="text/javascript"> 
    var prm = Sys.WebForms.PageRequestManager.getInstance(); 
    prm.add_initializeRequest(InitializeRequestHandler); 
    prm.add_endRequest(EndRequestHandler);        

    var pbQueue = new Array(); 
    var argsQueue = new Array();       

    function InitializeRequestHandler(sender, args) { 
        if (prm.get_isInAsyncPostBack()) { 
            args.set_cancel(true); 
            pbQueue.push(args.get_postBackElement().id); 
            argsQueue.push(document.forms[0].__EVENTARGUMENT.value); 
        } 
    }       

    function EndRequestHandler(sender, args) { 
        if (pbQueue.length > 0) { 
            __doPostBack(pbQueue.shift(), argsQueue.shift()); 
        } 
    } 
</script>

The Code in Detail

First, we use the PageRequestManager to set up handlers for the beginning and end of each asynchronous request:

var prm = Sys.WebForms.PageRequestManager.getInstance(); 
prm.add_initializeRequest(InitializeRequestHandler); 
prm.add_endRequest(EndRequestHandler);

Queuing up the Postbacks…

Then we create an array to store the originator of each asynchronous postback that cannot be processed immediately, as well as an array to store any event arguments associated with the postback:

var pbQueue = new Array(); 
var argsQueue = new Array();

Then, at the beginning of each asynchronous postback, we check to see if the page is already in an asynchronous postback:

function InitializeRequestHandler(sender, args) { 
    if (prm.get_isInAsyncPostBack()) {...}

If it is, we cancel the new postback request, and instead, add the event target and arguments to our arrays:

args.set_cancel(true); 
pbQueue.push(args.get_postBackElement().id); 
argsQue.push(document.forms[0].__EVENTARGUMENT.value);

…and Executing Them

After each asynchronous postback completes, we check to see if there are any more queued up, and if so, we do a __doPostBack(). pbQueue.shift() pulls the first item out of the array and removes it.

function EndRequestHandler(sender, args) { 
    if (pbQueue.length > 0) { 
        __doPostBack(pbQueue.shift(), argsQueue.shift()); 
    } 
}

And that’s it. Run the page, and randomly click some buttons! If you watch the browser’s status bar, you’ll see the asynchronous postbacks piling up. Then, every 3 ½ seconds, you’ll see one of them being processed! (Remember, the 3 ½ seconds is just an arbitrary time that we added into this demonstration, and it has nothing to do with how the code really works.)

Note: If for some reason, you wanted to execute the asynchronous postbacks in reverse chronological order (i.e., the most recent requests get processed first), just replace the array.shift() command in the EndRequestHandler() with array.pop().

December 12, 2007 Posted by | Ajax, ASP.NET, Javascript, Web Development | 10 Comments

Disabling a Trigger Control During Asynchronous PostBack

Often, we want to disable the control that triggered an asynchronous postback until the postback has completed. This prohibites the user from triggering another postback until the current one is complete.

The Code

First add a ScriptManager to the page, immediately following the <form> tag.

<asp:ScriptManager ID="ScriptManager1" runat="server" />

Then add a Label wrapped in an UpdatePanel. This label will be populated with the date and time on each postback. We’ll also add a Button inside of the UpdatePanel to cause the postback.

<asp:UpdatePanel ID="UpdatePanel1" runat="server"> 
    <ContentTemplate> 
        <asp:Label ID="Label1" runat="server" Text="Label" /><br /> 
        <asp:Button ID="Button1" runat="server" Text="Update Time" OnClick="Button1_Click" /> 
    </ContentTemplate> 
</asp:UpdatePanel>

We’ll also add an UpdateProgress control and associate it with our UpdatePanel just to let the user know that something’s happening.

<asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"> 
    <ProgressTemplate> 
        Loading... 
    </ProgressTemplate> 
</asp:UpdateProgress>

Next, we’ll add a events in the code-behind to populate the Label and to introduce some latency, simulating a lengthy update to the page.

VB.NET:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 
    Label1.Text = Now.ToString 
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) 
    System.Threading.Thread.Sleep(4000)  'Pause for 4 seconds. 
End Sub

And finally we’ll add the client-side code to disable our button during the postback. The Javascript disables the button during the beginRequest event of the PageRequestManager and enables it when control has been returned to the browser in the endRequest event. The control causing the postback is returned from the get_postBackElement() method of the BeginRequestEventArgs object which is passed to the function handling the beginRequest event.

Add the follow script after the ScriptManager on the page:

<script type="text/javascript"> 
    var pbControl = null; 
    var prm = Sys.WebForms.PageRequestManager.getInstance(); 
    prm.add_beginRequest(BeginRequestHandler); 
    prm.add_endRequest(EndRequestHandler); 
    function BeginRequestHandler(sender, args) { 
        pbControl = args.get_postBackElement();  //the control causing the postback 
        pbControl.disabled = true; 
    } 
    function EndRequestHandler(sender, args) { 
        pbControl.disabled = false; 
        pbControl = null; 
    } 
</script>

And that’s it!

The Complete Source Code:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %> 
<%@ Register Assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" 
    Namespace="System.Web.UI" TagPrefix="asp" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml" > 
    <head runat="server"> 
        <title>Untitled Page</title> 
    </head> 
    <body> 
        <form id="form1" runat="server"> 
            <asp:ScriptManager ID="ScriptManager1" runat="server" /> 
            <script type="text/javascript"> 
                var pbControl = null; 
                var prm = Sys.WebForms.PageRequestManager.getInstance(); 
                prm.add_beginRequest(BeginRequestHandler); 
                prm.add_endRequest(EndRequestHandler); 
                function BeginRequestHandler(sender, args) { 
                    pbControl = args.get_postBackElement();  //the control causing the postback 
                    pbControl.disabled = true; 
                } 
                function EndRequestHandler(sender, args) { 
                    pbControl.disabled = false; 
                    pbControl = null; 
                } 
            </script> 
            <asp:UpdatePanel ID="UpdatePanel1" runat="server"> 
                <ContentTemplate> 
                    <asp:Label ID="Label1" runat="server" Text="Label" /><br /> 
                    <asp:Button ID="Button1" runat="server" Text="Update Time" OnClick="Button1_Click" /> 
                </ContentTemplate> 
            </asp:UpdatePanel> 
            <asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"> 
                <ProgressTemplate> 
                    Loading... 
                </ProgressTemplate> 
            </asp:UpdateProgress> 
        </form> 
    </body> 
</html>

December 10, 2007 Posted by | Ajax, ASP.NET, Javascript, Web Development | 23 Comments

Maintain Scroll Position after Asynchronous Postback

Do you want to maintain the scroll position of a GridView, Div, Panel, or whatever that is inside of an UpdatePanel after an asynchronous postback?  Normally, if the updatepanel posts back, the item will scroll back to the top because it has been reloaded.  What you need to do is “remember” where the item was scrolled to and jump back to there after the postback.  Place the following script after the ScriptManager on your page.  And since the _endRequest event of the PageRequestManager happens before the page is rendered, you’ll never even see your item move!

<script type="text/javascript"> 
    var xPos, yPos; 
    var prm = Sys.WebForms.PageRequestManager.getInstance(); 
    prm.add_beginRequest(BeginRequestHandler); 
    prm.add_endRequest(EndRequestHandler); 
    function BeginRequestHandler(sender, args) { 
        xPos = $get('scrollDiv').scrollLeft; 
        yPos = $get('scrollDiv').scrollTop; 
    } 
    function EndRequestHandler(sender, args) { 
        $get('scrollDiv').scrollLeft = xPos; 
        $get('scrollDiv').scrollTop = yPos; 
    } 
</script>

December 3, 2007 Posted by | Ajax, ASP.NET, Javascript, Web Development | 35 Comments