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What is Event?

Event:-The Event model in C# finds its roots in the event programming model that is popular in asynchronous programming. The basic foundation behind this programming model is the idea of "publisher and subscribers."

            using System;
using System.IO;

namespace EventExample
      public class MyClass
     public delegate void  LHandler(string message);
        // Define an Event based on the above Delegate
        public event LHandler Log;
        // Instead of having the Process() function take a delegate
        // as a parameter, we've declared a Log event. Call the Event,
                public void Process()
            OnLog("Process() begin");
            OnLog("Process() end");
           protected void OnLog(string message)
            if (Log != null)
    // The FLog class merely encapsulates the file I/O
    public class FLog
        FileStream fileStream;
        StreamWriter streamWriter;
        // Constructor
        public FLog(string filename)
            fileStream = new FileStream(filename, FileMode.Create);
            streamWriter = new StreamWriter(fileStream);
        // Member Function which is used in the Delegate
        public void Logger(string s)
        public void Close()
       public class TestApplication
        static void Logger(string s)
        static void Main(string[] args)
            FLog fl = new FLog("process.log");
            MyClass myClass = new MyClass();
            // Subscribe the Functions Logger and fl.Logger
            myClass.Log += new MyClass.LHandler(Logger);
            myClass.Log += new MyClass.LHandler(fl.Logger);

            // The Event will now be triggered in the Process() Method
Compile an test: 
# csc EventExample.cs
# EventExapmle.exe
Process() begin
Process() end
# cat process.log
Process() begin
Process() end 

An event is a placeholder for code that is executed when the event is triggered, or fired. Events are fired by a user action, program code, or by the system.

    The following important conventions are used with events:

        * Event Handlers in the .NET Framework return void and take two parameters.
        * The first paramter is the source of the event; that is the publishing object.
        * The second parameter is an object derived from EventArgs.
        * Events are properties of the class publishing the event.
        * The keyword event controls how the event property is accessed by the subscribing classes.

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