Anonymous methods in C#

Introduction

As you may know, if the caller want to respond to any event, it must create a method -(event handler) that matches the signature of it's associated delegate. Such method is only called by the event associated delegate object.

(if you don't know about delegates and events see my articles Delegates in C#, Events in C#).

Example

public class MyClass
{
    public delegate void MyDelegate(string message);
    public event MyDelegate MyEvent;
    public void RaiseMyEvent(string msg)
    {
        if (MyEvent != null)
            MyEvent(msg);
    }
}
class Caller
{
    static void Main(string[] args)
    {
        MyClass myClass1 = new MyClass();
        myClass1.MyEvent += new MyClass.MyDelegate(myClass1_MyEvent);
        myClass1.RaiseMyEvent("Hiii");
    }
    //this method called only by MyDelegate
    public static void myClass1_MyEvent(string message)
    {
        //do some thing to respond to the event here
    }
}

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As you can see, event handler methods such as (myClass1_MyEvent) are never called by any part of the application other than the invoking delegate so you need it only to handle you event.

You can associate a delegate directly to a block of code statements at the time of event registration. Such code is named anonymous method.

The next example will show you how to handle the events using anonymous methods:

namespace AnonymousMethods
{
    public class MyClass
    {
        public delegate void MyDelegate(string message);
        public event MyDelegate MyEvent;
        public void RaiseMyEvent(string msg)
        {
            if (MyEvent != null)
                MyEvent(msg);
        }
    }
    class Caller
    {
        static void Main(string[] args)
        {
            MyClass myClass1 = new MyClass();
            //Register event handler as anonymous method.
            myClass1.MyEvent += delegate
            {
                Console.WriteLine("we don't make use of your message in the first handler");
            };
            //Register event handler as anonymous method.
            //here we make use of the incoming arguments.
            myClass1.MyEvent += delegate(string message)
            {
                Console.WriteLine("your message is: {0}", message);
            };
            //the final bracket of the anonymous method must be terminated by a semicolon.
            Console.WriteLine("Enter Your Message");
            string msg = Console.ReadLine();
            //here is we will raise the event.
            myClass1.RaiseMyEvent(msg);
            Console.ReadLine();
        }
    }
}

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Notice that when you use the anonymous methods you don't need to define any static event handlers. Rather, the anonymous methods are defined at the time the caller is handling the event.

Note: You are not required to receive the incoming arguments sent by a specific event. but if you want to make use of the incoming arguments you will need to specify the parameters defined by the delegate type (just like the second handler in the previous example).

Example

myClass1.MyEvent += delegate(string message)
{
    Console.WriteLine("your message is: {0}", message);
};

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we're done, I hope you now have a good understanding of anonymous methods in C#.