Just put both the dropdownlist inside different Updatepanel. ( Say Ddl1 is in inside UpdatePanel1 and ddl2 is inside update panel2 )
Now Change the UpdateMode of UpdatePanel2 to “Conditional” . And Update the UpdatePanel2 on the selectionIndex Changed of Ddl1 as UpdatePanel2.Update()
Hope Rest part you will do yourself !!!
I have a textbox with a RegularExpressionValidator and a ValidatorCallOutExtender and ontextchanged event i call RegularExpressionValidator.validate() but ValidatorCallOutExtender doesn't fire and no erro message appear.
My friend, you will need to read about User Controls and Page Life cycle as well in order to create your dynamic controls at runtime, not hard if you got the idea right, and I believe CP has some articles on creating dynamic controls at runtime in asp.net, for saving the data I don't see this as an issue ... it will be as just any other static user control.
Sincerely Samer Abu Rabie
Note: Please remember to rate this post to help others whom reading it.
You are creating dynamic controls without having proper knowledge on ASP.NET page life cycle and viewstate. ASP.NET will not maintain viewstate for your dynamic control as it is created in button click event.