Implement the ICallbackEventHandler interface for any custom control that needs to receive callback events. For more information, see Implementing Client Callbacks Programmatically Without Postbacks in ASP.NET Web Pages.

Examples of controls that implement the ICallbackEventHandler interface include the GridView, DetailsView, and TreeView controls. When a callback event targets a control that implements the ICallbackEventHandler interface, the RaiseCallbackEvent method is called to handle the event, passing the event argument as a parameter and the GetCallbackResult method returns the result of the callback.

Controls that retrieve data from a data source control during callback can do so synchronously or asynchronously. ASP.NET controls like GridView, DetailsView, and TreeView are implemented synchronously. Synchronous callbacks do not prevent the user from working in the browser. In synchronous mode, only one callback at a time can execute, with the last callback taking precedence. When a Web control is implemented to support asynchronous behavior, multiple callbacks can be raised simultaneously. For details on asynchronous programming, see Asynchronous Programming Design Patterns.

You can specify whether callback events originating from the user interface rendered by a control implementing the ICallbackEventHandler interface are validated. Validation of events is a good security practice. However, for performance reasons you can disable it. To control whether event validation is performed on callback events, set the enableEventValidation attribute of the @ Page directive or the enableEventValidation attribute of the pages Element (ASP.NET Settings Schema) of the Web.config file. If you set the EnableEventValidation property in code, set it in the Page_Init phase of page processing. For more information on balancing the security benefit of event validation with its performance cost, see Performance Overview.

• AspNetHostingPermission 

  for operating in a hosted environment. Demand value: LinkDemand; Permission value: Minimal.

• AspNetHostingPermission 

  for operating in a hosted environment. Demand value: InheritanceDemand; Permission value: Minimal.

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Reference