ASP.NET Ajax ServerControls

ASP.NET Ajax server controls consist of server and client code that integrate to produce rich client behavior. The following list describes the most frequently used Ajax server controls.

1. ScriptManager Control
2. UpdatePanel Control
3. UpdateProgress Control
4. Timer Control

The ScriptManager control is the essential core for the AJAX Extensions that makess ASP.NET AJAX possible by managing the JavaScript for you behind the scenes. There are a number of client script libraries available to ASP.NET developers, and when a ScriptManager is used, only the relevant ones are downloaded to the client. Moreover ScriptManager control supports the UpdatePanel controls to handles the asynchronous postbacks and refreshes only the regions of the page that have to be updated (partial-page rendering). The ScriptManager control will be visible in design view but will not be visible when the web site is run.

UpdatePanel control is used to visually design the part of the page that is used in partial-page rendering. Placing controls inside an UpdatePanel control enables you to refresh selected parts of the webpage instead of refreshing the whole page with a postback to the webserver. When the UpdatePanel control performs an asynchronous post, it adds a custom HTTP header. There is no limit to the number of UpdatePanel controls that can be on a page, and they can be nested. Each UpdatePanel is updated individually and asynchronously, without affecting one another or anything else on the page.

UpdateProgress control shows the status information for the progress of the download occurring in the UpdatePanel. The page can contain multiple UpdateProgress controls. Each one can be associated with a different UpdatePanel control. Alternatively, you can use one UpdateProgress control and associate it with all the UpdatePanel controls on the page.

The Timer control enables you to perform postbacks at a specified interval. It can be used to trigger automatic updates to an area of the page that is wrapped with an UpdatePanel.