what's the difference between delegates and events

Question

Hi what's the difference between delegates and events?

Vulpes · Answer

Although it may not always be apparent an event is really a special kind of 'Sub' delegate. If you don't declare an event using an existing delegate type then the VB.Net compiler creates one for you and unless you're declaring a 'custom' event it also creates methods to add handlers remove handlers and raise the event behind the scenes. Events are restricted in what can be done with them (and have special keywords to enforce these restrictions) compared to normal delegates. The only operations which you are allowed to do (without resorting to reflection) are: 1. To subscribe to the event (using WithEvents/Handles or AddHandler). 2. To unsubscribe from the event (using RemoveHandler). 3. To raise the event (using RaiseEvent) though this can only be done from the type in which the event is declared. This means that there is no easy way to examine or modify the event's invocation list and to therefore know what other methods have subscribed to the event.