In this demo, the combo box in the City column (the City combo box) is populated dynamically with city names via callbacks, based on the value selected in the combo box in the Country column (the Country combo box). Only the content stored in the City combo box is updated during round-trips to the server - not the content of the page or the DevExpress ASP.NET Grid View (ASPxGridView) control.
The client-side SelectedIndexChanged event of the Country combo box is handled to update the City combo box. On the server side, the Callback event is handled to populate the City combo box with required values.