Atlas ScriptManager Control

Very important to learn the basics in atlas ajax programming. NK's blog once agian has a sexy introduction to this

Dynamic CascadingDropDownExtender Control and Viewsate

Spent some time at work trying to get the cascadingdropdown extender control (that comes with AJAX tollkit ) to work according to my needs. The intention was not to do some thing very complicated , a simple page with dynamic controls ( parent-child chain of dropdowns) being added at runtime. Looking at the sample app that ships with the ajax toolkint tells at best the different usage of each controls\extenders.

• Preset a default value: One bit where I was challanged in the start was to get my drop downs populated with a default value ( like when you open a page in edit mode ) , it took me a while to figure out that setting SelectedValue property of the cacading extender control actually sets the default value and not by simply adding items to the dropdown , something that we would usually do. Another interesting thing to notice was that the default value gets set via an ajax call after the page is rendered on client side ( browser ).

• Viewstate: Another thing I did not get working in the first go was , persisting the dropdown viewstate after a post back. The client side script was working its job all fine with the parent-child data coming as response with the asynchronous ajax calls,etc. It was in the end ( when I thot all the hardship is over ) I realised that the selected value of the dropdowns wre not available after a postback ( dejavu... dynamically added controls ). Although I did make sure to give the same ID for the respective dropdowns to have the 'dynamic control viewstate' theory do the rest of the job for me , but not so lucky. After a bit of googling found out that if I add these controls in the OnInit function ( override OnInit and add the control dynamically here ) rather than page load it works perfect. .... i always have hate this solution. I ended up using the old asp way of getting the value from the form request bag. ( Request.Form[dropdownList1.UniqueID] )

Asp.Net link for this control. ( forum )