Some Ajax tips and tricks

Introduction

Microsoft Ajax 1.0 has just been released! (http://go.microsoft.com/fwlink/?LinkID=77296).

In syncronous web forms it's easier to interact with the user, because he/she sees the page flashing back and processing (which is undesirable). With Ajax, you can add an update progress panel, and put an animated gif inside. But what if you want to display an hourglass? In this article I will show 2 tricks.

Diplay an hourglass

The following javascript code snippet nicely does the job:

<scriptmanager id="ScriptManager1" runat="server" />
<script language="JavaScript">
var prm = Sys.WebForms.PageRequestManager.getInstance();
    prm.add_initializeRequest(InitializeRequest);
    prm.add_endRequest(EndRequest);
    function InitializeRequest(sender, args) {
     document.body.style.cursor = "wait";    
    }
    function EndRequest(sender, args) {
     document.body.style.cursor = "default";    
    }
</script>

I have received several criticism due to the length of this article, so I have decided to rename it as: some Ajax tips & tricks.

Click-once button control

Lots of attempts have been made to create a click once button...Some of them are quite complex (http://www.codeproject.com/aspnet/ClickOnce_Button_Control.asp).
I've been searching the internet for a click once submit button, but wihout success. Some of them cause post-back, which is undesirable, while others don't work with validation controls. And it's so useful, because it prevents users to click twice on the same button, thus leading to possible bugs and misleading behavior.

Combining the content of the first tip, we can achieve a good result, as shown in the picture below:

<scriptmanager id="ScriptManager1" runat="server" />
<script language="JavaScript">

var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_initializeRequest(InitializeRequest);
prm.add_endRequest(EndRequest);

var btn;

function InitializeRequest(sender, args) 
{
 document.body.style.cursor = "wait";                
 var btnId=args._postBackElement.id;
 btn= document.getElementById(btnId);
 if (btn.type=="button" || btn.type=="submit") 
   btn.disabled=true;
}

function EndRequest(sender, args) 
{                
 document.body.style.cursor = "default";    
 if(btn!=null) btn.disabled=false; 
}
</script>

Code explanation:

In the InitializeRequest function we retrieve the pressed button id, by retrieving the _postBackElement which is passed as an argument, and after we verify if it is a button.
We must declare the button variable as a global variable, to allow the EndRequest function to know which button fires the event.

Note that the above function will work ONLY if the button control is inside an UpdatePanel. And that's it! We have a click-once button! We can even put it in a MasterPage to propagate behavior to your content pages...