AJAX-Enabled Web-Parts: solving the problem of changing Client IDs

One of the most challenging aspects of building SharePoint-enabled web parts is using JavaScript to interact with specific controls. As a consequence of how SharePoint renders controls with id’s in Sharepoint WebParts, it’s near impossible to write clean JavaScript.

From a maintenance perspective I HATE using server-side code to render JavaScript. It’s inelegant and reeks of a lack of forethought. Yuck yuck yuck. It’s like sweeping dust under the rug.

Wherever possible, webpart-specific javascript should be held within a single .js file (stored in the 12Hive). The problem is that Sharepoint alters a control’s ID during the page rendering process.

So, a label with the ID “label1” might become “ctl00_label1”. The naming process is entirely unpredictable.

This makes interacting with a specific DIV, INPUT or any other html element very difficult because you can’t predict the rendered IDs during development. This is especially problematic if you’re looking to host several instances of a webpart on a single page.

One really terrible way of dealing with this is to render the html yourself by adding literal controls ala

	LiteralControl l = new LiteralControl();
	l.text = “
blah
”;
	this.Controls.Add(l);

This is a terrible approach which is severely limiting and unnecessary.

To tackle the problem I’ve devised the following solution which revolves around creating a Javascript class to accompany the web part:

• create properties to store the dynamically generated IDs of every html component to wish to interact with
• create pointers to every html component you wish to interact with
• create an init function. As input you pass the clientID of the webpart AND the id’s of every component you wish to interact with.

• this function will store the id’s using the properties
• this function will also attach the pointers to their respective objects
• this function should also attach any eventhandlers
• create any supporting functions (i.e. webservice calls, webservice receivers)

This approach embraces the absence of reliable identification info. It is also sympathetic to having multiple copies of a webpart on the same page.

Here’s what the javascript might look like

function UpdatingLabelWebPart()
{
	var me = this;	//required to reference the object at runtime
	this.clientID = null;	//ids
	this.labelID = null;
	this.buttonID = null;
	this.label = null;	//controls
	this.button = null;
	this.register = function (clientID, labelID, buttonID)
	{
		me.clientID = clientID;		//init the id
		me.labelID = labelID;
		me.buttonID = buttonID;
		me.attachToButton();
	}
	this.attachToButton = function()
	{
		//if the controls haven't loaded yet
		if (document.getElementById(me.buttonID) == null || document.getElementById(me.labelID) == null)
		{
			setTimeout(me.attachToButton, 50);
		}
		else
		{
			//register the controls
			me.label = document.getElementById(me.labelID);
			me.button = document.getElementById(me.buttonID);
			//attach any events
			button.AttachEvent("click", me.buttonClicked);
		}
	}
	this.buttonClicked = function(sender, args)
	{
		me.label.innerHTML = "Hello World";
	}
}

Then in your webpart you write a teeny tiny bit of javascript which you register as a clientscriptblock.

String myScriptBlock = String.Format(@"
					var tmp = new UpdatingLabelWebPart();
					tmp.register('{0}','{1}','{2}');
				    ", this.clientID
				    , this.label1.clientID
				    , this.button1.clientID);
Page.ClientScript.RegisterClientScriptBlock(typeof(Page), "UpdatingLabelWebPartJS",myScriptBlock, true);
Page.ClientScript.RegisterClientScriptInclude(GetType(), GetType().ToString(), "_layouts/1033/myJS/UpdatingLabelWebPart.js");

This approach lets you have multiple instances of the same AJAX-enabled webpart and saves you the hassle of having to write annoying javascript (having to write me.label is hardly a chore).

I came across an annoying problem when playing with the ASP.NET Ajax extensions earlier today.  I was trying to call a script-enabled web-service but kept getting a javascript error telling me my service was undefined.  It’s been a month or so since I’ve used MS Ajax and needed a refresher.

Some background:

• My project namespace is ajaxTest
• My webservice class is helloTest
• My webservice function is helloWorld

I enabled the web service using the [System.Web.Script.Services.ScriptService()] attribute

I put the script manager code block in place and included a reference to the service.

<asp:ScriptManager ID=”ScriptManager1″ runat=”server”>
<Services>
<asp:ServiceReference Path=”helloTest.asmx” />
</Services>
</asp:ScriptManager>

I then created some javascript to call the web service

function testScriptService()
{
var tmp = helloTest.helloWorld(onResult, onTimeout, onError);
}

It was at this point I received the “helloTest is undefined” message.

A quick search on google revealed two websites which helped me.  The first had the right answer (in my situation).  Strangely, the second website had a slightly different solution which seems to have helped a number of people, but I was unable to figure out why (I didn’t work for me).

So, the solution that worked:

You need to fully qualify the javascript with the namespace of your webservice.

Namespace.Class.Function >> ajaxTest.helloTest.helloWorld

The solution which didn’t work for me but has worked for others is to use the following structure:

Namespace.Services.Class.Function >> ajaxTest.Services.helloTest.helloWorld

No idea why the difference, but hey.

Credit where credit’s due, thanks to Omen’s blog and Ryan at Solutek.