Using events

C# allows classes to notify other pieces of code when an action occurs in the class. This capability is called the event mechanism, and it enables callers to be notified when an event occurs in a C# class. You can design C# classes to notify other pieces of code when certain events take place in the class. The class can send an event notification back to the original piece of code.

You may want to use an event, for example, to inform other pieces of code when a lengthy operation completes. Suppose, for example, that you're designing a C# class that reads from a database. If the database activity is going to take a long time, it may be better for another piece of code to do other things while the database is being read. When the read is complete, the C# class can fire an event that says "the read has completed." Other pieces of code can be notified when this event is sent out, and the code can take appropriate action when the event is received from the C# class.

Cross-Reference The event-handling mechanism in C# works in conjunction with another C# concept called a delegate. You take closer look at delegates and events in Chapter 15, "Events and Delegates."

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