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Asked: 2026-05-26T13:38:45+00:00

I’m using VS2010,C# to develop my ASP.NET web app. I have some a combo

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I’m using VS2010,C# to develop my ASP.NET web app. I have some a combo box for selecting province and another combo box for selecting cities, when user selected a province, the city combo box should immediately display cities belonging to that province.
I have inserted an AJAX script manager into my page, also an AJAX update panel (both from toolbox) in which I’ve inserted my combo boxes. Then I enabled province combo box autopostback property so that when user changes his selection, I can detect it and change contents of city combo box accordingly.
It works fine, as I load province and city names from my database into a list at page startup (of course this load process is performed in a if(!IsPostback) statement so that data is loaded only once). I think the time needed to update city combo box is a bit more than what is required, as there is a postback when user changes province combo box selection, what is the best (and correct) way of performing this operation? is it ok? are there any better ways of doing it? how can I IMMEDIATELY update city combo box after province combo box selection is changed, as currently there is a short delay.

thanks

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  1. Editorial Team

    You’re always going to have a delay if you do it on the server side with an ASP.NET postback.

    Another option would be to output some JSON to your page on initial load which contains an array of all your provinces with a nested array for each province containing its respective cities.

    Then you can remove the auto postback and do everything client side with JavaScript. Whenever the selected province changes you just need to parse your JSON and add all the associated cities to the second dropdown list.

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