Module 11 - Events

Module 11: Events By SRIRAM . B

Overview 

Events 

What is an event?

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How events work?

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Defining an event

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Handling an event

Events 

Events allow an object to notify other objects that a change has occurred. The other objects can register an interest in an event, and they will be notified when the event occurs.

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How Events work? 

Publisher raises an event to alert all interested objects (subscribers)

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Subscriber provides a method to be called when the event is raised

Defining an event event mydelegate myevent; (To be declared within the class)

Events 

Subscribing to an Event obj.myevent = new mydelegate(obj.my); obj.myevent += new mydelegate(obj.my1);

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Notifying obj.myevent();

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Passing parameters to events 

Derive a class from EventArgs

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Have the necessary get methods

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Create the delegate with 2 parameters one is the sender and the other is the eventargs

Handling an event 

To handle an event we need to subscribe to the event by providing an event handler function whose signature matches that of delegate specified for use with the event.

Example - Events using System; using System.Timers; namespace events { public class EventHandler2 {

static int counter = 0;

static string str = "STG INTERNATIONAL LIMITED"; public static void WriteChar(object o, ElapsedEventArgs e) { Console.WriteLine(str[counter++ % str.Length]); }

Example - Events static void Main(string[] arg) {

Timer tm = new Timer(100); tm.Elapsed += new ElapsedEventHandler(WriteChar); tm.Start();

}

}

}

Console.ReadLine();

Session Ends

Exercise

Relax