Assembly: System.Web (in System.Web.dll)
Page developers can provide custom handlers for Web Parts events by adding an OnSelectedWebPartChanging attribute, OnWebPartClosing attribute, or OnWebPartDeleting attribute to the <asp:webpartmanager> element in a page, and assigning a custom method name to the attribute. A custom handler can also be assigned programmatically. For more information on programmatically assigning an event handler, see How to: Connect Event Handler Methods to Events.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.