A ViewEventHandler delegate method compares the EventType property to the static ViewEvent fields to determine which type of action raised the event. A ViewEvent object is equal to TemplateModeChanged to indicate that the template editing mode changed for a control on the design surface.
The ControlDesigner class supplies a default ViewEventHandler delegate. If the event type is TemplateModeChanged, the delegate sets the value for the InTemplateMode property.
Custom designers that are derived from the TemplatedControlDesigner class can override the OnTemplateModeChanged method to perform additional processing when the template editing mode changes for a control on the design surface.