Tuesday, February 06, 2007

ASP.NET Ajax, enabling/disabling Ajax on the same software project

First of all, to turn a normal ASP.NET application to Ajax takes only a few minutes with the Microsoft Ajax.Net platform. It's as easy as moving some of the content in UpdatePanels and adding a ScriptManager. Of course, you need the Ajax.Net package installed.

What I am going to talk about is a simple way to enable/disable Ajax, and keeping the entire basic functionality intact. Why would I do that? Because sometimes you need to see the project working on a computer that doesn't have the Ajax framework installed. You might even want to work on the project itself. So this is what you do:

First of all, the ScriptManager control must appear on every Ajax page in the project, so why not move it to the MasterPage? Yes. Only one ScriptManager in the MasterPage suffices. Second of all, the UpdatePanel and the UpdateProgress controls are nothing more than normal Panels with the cool Ajax functionality added to them. So enabling or disabling Ajax surmounts to nothing more than replacing these controls with normal panels.

So here is the quick method of enabling, disabling Ajax.Net whenever you want:
Start off from the Ajax enabled application and save the web.config as web.config.ajax. Remove everything from it that resembles System.Web.Extensions and all other weird things that Ajax.Net adds to the web.config except this:
<system.web>
<pages>
<controls>
<add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
</controls>

this you only replace with this:
<system.web>
<pages>
<controls>
<add tagPrefix="asp" namespace="System.Web.UI" assembly="MockAspNetAjax"/>
</controls>

Save it to Web.config.noajax

You might see where I am going already. Now create a new Visual Studio project, a class library, one that you will use for all these conversions, and call it MockAspNetAjax. Go to the project Properties and change the default namespace to System.Web.UI. Add three classes that do nothing but inherit from Panel: ScriptManager, UpdatePanel, UpdateProgress. The UpdateProgress will have some additional code:
 public UpdateProgress()
{
Init += new EventHandler(UpdateProgress_Init);
}

void UpdateProgress_Init(object sender, EventArgs e)
{
Visible = false;
}

because you don't want to see the Ajax Update Progress message continuously on your page.

In order to convert an ASP.NET Ajax application to a normal postback application you follow two simple steps:
1. overwrite the web.config with web.config.noajax
2. add MockAspNetAjax as a reference or include in the project if previously excluded.

back to Ajax:

1. overwrite the web.config with web.config.ajax
2. remove MockAspNetAjax as a reference or exclude the dll from the project, while keeping the dll there.

That's it!

Of course, Ajax has a lot more stuff to it, like for example the [ScriptService] web services that are directly accessed from Javascript. Or Ajax enabled controls or other controls which don't even work without the framework. These are more complex situations which cannot be solved with such a general solution, but the same basic principles apply: use web config to avoid Register tags in each page, replace controls with mockup controls, remove HttpHandlers and HttpModules, replace javascript code that uses Ajax with something that does nothing or emulates the same behaviour (preferably) through postbacks or hidden iframes, etc.

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