Avoid (Prevent) Page refresh (PostBack) after SelectedIndexChanged is fired in ASP.Net DropDownList

Here Mudassar Ahmed Khan has explained with an example, how to avoid (Prevent) Page refresh (reload) after SelectedIndexChanged is fired in ASP.Net DropDownList using C# and VB.Net. The only possible way is to place the DropDownList inside ASP.Net AJAX UpdatePanel so that, instead of Full PostBack which causes Page refresh (reload), a Partial PostBack will occur.