A System.Web.UI.Design.ViewEventHandler delegate method compares the ViewEventArgs.EventType property to the static System.Web.UI.Design.ViewEvent fields to determine which type of action raised the event. A System.Web.UI.Design.ViewEvent object is equal to ViewEvent.Click to indicate that you clicked a region on the design surface.
The System.Web.UI.Design.ControlDesigner class supplies a default System.Web.UI.Design.ViewEventHandler delegate. If the event type is ViewEvent.Click, the delegate calls the ControlDesigner.OnClick(DesignerRegionMouseEventArgs) method. Classes deriving from the System.Web.UI.Design.ControlDesigner class override the ControlDesigner.OnClick(DesignerRegionMouseEventArgs) method to handle click events on a region at design time. The event arguments indicate which designer region was clicked, if any.