Occurs during the process of changing which WebPart or server control is currently selected on a Web page.
Assembly: System.Web (in System.Web.dll)
This event can be used in conjunction with the OnSelectedWebPartChanging method. Page developers can create an event handler in their code by adding the OnSelectedWebPartChanging attribute to the <asp:webpartmanager> element in a page, and setting the value of the attribute to the name of a custom method that will handle the event.
This event is raised during the process of beginning or ending a connection between controls, and when beginning and ending an edit of a control. For details, see the OnSelectedWebPartChanging method.
Normally, when the event is raised as a direct result of a user's action that changes the selected control, the event can be cancelled. However, there is a scenario in which the event cannot be cancelled. If a WebPartZone control is deleted, the WebPart controls it contains must all be closed, otherwise they would be orphaned. In this case the WebPartManager control closes the WebPart controls, not the user, and it must determine which control is currently selected and when to change the selection without any chance of interruption, so that it can complete the process of cleaning up all the controls. Therefore, by design the method cannot be cancelled in this scenario. For a related event that can be cancelled, see the WebPartClosing event.