Assembly: System.Web (in System.Web.dll)
The method raises the WebPartClosing event to indicate that a control is in the process of being closed or removed from a page. The method also provides the option to cancel the closing process. If the control is successfully removed from the page, the WebPartClosed event follows.
Page developers can provide a custom handler for the associated event by adding the OnWebPartClosinging attribute to the <asp:webpartmanager> element on a Web page, and then assigning a custom method name to the attribute.Notes to Inheritors
Developers who create derived WebPartManager classes can override the method to customize the event handling.