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Deeksha Sharma

A delegate is a type that holds a reference to a method. A delegate is declared with a signature that shows the return type and parameters for the methods it references, and can hold references only to methods that match its signature. A delegate is thus equivalent to a type-safe function pointer or a callback. A delegate declaration is sufficient to define a delegate class.

Delegates have many uses in the .NET Framework. In the context of events, a delegate is an intermediary (or pointer-like mechanism) between the event source and the code that handles the event. You associate a delegate with an event by including the delegate type in the event declaration, as shown in the example in the previous section. For more information about delegates, see the Delegate class.

The .NET Framework provides the EventHandler and EventHandler<TEventArgs> delegates to support most event scenarios. Use the EventHandler delegate for all events that do not include event data. Use the EventHandler<TEventArgs> delegate for events that include data about the event. These delegates have no return type value and take two parameters (an object for the source of the event and an object for event data).

Delegates are multicast, which means that they can hold references to more than one event-handling method. For details, see the Delegate reference page. Delegates provide flexibility and fine-grained control in event handling. A delegate acts as an event dispatcher for the class that raises the event by maintaining a list of registered event handlers for the event.

For scenarios where the EventHandler and EventHandler<TEventArgs> delegates do not work, you can define a delegate. Scenarios that require you to define a delegate are very rare, such as when you must work with code that does not recognize generics. You mark a delegate with the delegate in (C#) and Delegate (in Visual Basic) keyword in the declaration. The following example shows how to declare a delegate named ThresholdReachedEventHandler.

public delegate void ThresholdReachedEventHandler(ThresholdReachedEventArgs e);
Posted on Friday, December 12, 2014 6:33 AM | Back to top

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