The first thing that I looked at was the method signature of the webservice. The documentation indicates that you need to use one of the following method signatures :

..OR..

What the documentation doesn’t tell you is that the name/spelling/capitalization of the method signature must match EXACTLY. If you decide that you don’t like the camelcase on the prefixText and want to use prefixtext instead….IT WON’T WORK. So make sure you have those signature matching correctly. I have seen some indications on the internet that you should use a static method such as :

DON’T DO THIS. It doesn’t work. Only the exact methods defined in the documentation and shown above will work.

Back to my project, I get these methods defined properly, compile the project, go to my textbox start to type and still I get NOTHING. So I look over the documentation and see some information about the class/method attributes that must be added. The documentation shows the following :

What they don’t show in the documentation is that you need to also add the following to the class definition

So I make these changes and run the application again, and STILL it doesn’t work. I’m stumped. I put a break at the webservice method and run again and it’s not even hitting the webservice. After a little bit of digging I come across Adding ASP.NET AJAX Configuration Elements to an Existing Web Site and a lightbulb goes on. This project was not setup as an AJAX.NET site, in fact it predates ASP.NET AJAX by a couple of years. Sure enough as I start to dig through the documentation I notice mappings to handlers for the webservice calls. So I follow the changes specified and run the site and it worked!

It took me a while to get this figured out, and I suspect there might be a few others out there that might have some problems getting this working. Below is a complete class that you can use as a reference. I haven’t included any of the code defining the AutoCompleteExtender because the documentation seems sufficient and I didn’t have any problems. There is also a video on the ASP.NET AJAX site that walks you through configuring your first AutoCompleteExtender and does a good job, as long as your site is configured properly!

Good luck!