Dropdown list from dataview

[SkydivingSteve]

I have two dropdown lists; Building and room number. They are both poplated from a database. So far so good. When the Building is selected, I want the Room number to relate only to the appropriate building. I can do this easy with two trips to the server. I want to do it with one trip only. So, on PageLoad a dataset is populated with all Room numbers for all buildings. On SelectedIndexChanged for Building, I want to filter the DataSet with only the appropriate rooms.

Is this, as my PE teacher used to say, "Clear as Mud"?

Any pointers or examples would be appreciated.

Thanks,

Steve

 

[RTomes]

Make the extra trip. This one I have tried over and over.
You can manipulate the dropdowns with server side java script and even get data back using a silent postback trick simular to calling a client side web service. The problem lies when you post back to the server and the server has no idea what items have been added or removed to the list boxes. It only knows what it retrieves from viewstate. You quickly start leaving .Net and go back to the past days with ASP classic.