AJAX Popup extender control provides the functionality to display the list of items in the form of context for textbox control. You can use the ASP.Net repeater control, radiobutton list control or checkbox list control to display the popup menus using AJAX Popup extender that will look more interactive than old style basic Dropdownlist controls. AJAX Popup control automatically returns the selected value that can displayed on web page without refreshing the page.
Properties of AJAX Popup Control
You can learn the use of above properties and get the C# code from the tutorial of AJAX Popup control by following the link provided at the bottom of this sample.
Try the sample below to understand the functionality of AJAX Popup control. In the following sample we have used radio button list control to popup at click event of textbox control: