Question

I need to develop a page which has 2 dropdownlist.

Options of dropdownlist 2 are based on selection of dropdownlist 1.

I have 2 methods to change the dropdownlist 2. What will you choose?

1:
Postback when users select dropdownlist 1 and change dropdownlist 2.
Pros:
Can use the postback feature, can use the asp.net validator
Cons:
Need to communicate with server (more traffic)
Users will see the page loading in the status bar.

2:
Get all the data (not very much data) in a JSON object when loading the page and change the dropdownlist 2 using javascript.
Pros:
Don’t need to communicate with server(less traffic)
Cons:
Can’t use the postback feature and validator and more troublesome to write server validation.

Also, I usually write the JSON object to the page as follows:

var locations = <asp:Literal runat="server" id="litLocation" text="[]" />

And then set the “litLocation” in page_load after the data is processed by datacontractjsonserializer.
Do you do it in the same way?

Answer 1

I prefer the second option, no need to reload the whole page just to refresh one dropdown list. I’d also do the client side dev in jQuery, much easier. You can do the client side validation for the change event of the first dropdown in jQuery as well, and keep the form submit validation in ASP.NET.

Have a look at the selectChain plugin for jQuery (demo’s etc here).