The UpdatePanel control is a server control which used to achieve asynchronously postback of limited to regions of the page.
This process is coordinated by the ScriptManager server control.
By default, any postback control inside an UpdatePanel control causes an asynchronous postback and refreshes the panel’s content. However, you can also configure other controls on the page to refresh an UpdatePanel control. You do this by defining a trigger for the UpdatePanel control.
<asp:AsyncPostBackTrigger ControlID=”Button1″ />
A trigger’s control event is optional. If you do not specify an event, the trigger event is the default event of the control.
UpdateMode (Always, Conditional)
If the UpdateMode property is set to Always, the UpdatePanel control’s content is updated on every postback that originates from anywhere on the page. This includes asynchronous postbacks from controls that are inside other UpdatePanel controls, and postbacks from controls that are not inside UpdatePanel controls.
If the UpdateMode property is set to Conditional, the UpdatePanel control’s content is updated when one of the following is true:
- When the postback is caused by a trigger for that UpdatePanel control.
- When you explicitly call the UpdatePanel control’s Update() method.
- When the UpdatePanel control is nested inside another UpdatePanel control and the parent panel is updated.
To use an UpdatePanel control in a master page, you must decide how to include the ScriptManager control. If you include the ScriptManager control on the master page, it can act as the ScriptManager control for all content pages.
UpdatePanel controls can be nested. If the parent panel is refreshed, all nested panels are refreshed also.