MulticastDelegates.cs

using System;

/* Multicast Delegates
 * 
 * A multicast delegate is a delegate that has a reference to more than one function.
 * When you invoke a multicast delegate, all of the functions the delegate is pointing to are invoked.
 * 
 * There are 2 approaches to create a multicast delegate (multiple instances, or the same instance)
 *      1. + or += to register a method with the delegate (SEE APPROACH ONE)
 *      2. - or -= to un-register a method with a delegate (SEE APPROACH TWO)
 * 
 * Important: A multicast delegate invokes the methods in the invocation list in the same order in which they are added
 * 
 * If the delegate has a return type other than void, and if the delegate is a multicast delegate, only the value of the last
 * invoked method will be returned.
 * 
 * If the delegate has an output parameter, the value of the output parameter will be the value assigned by the last method
 * 
 * !!Interview Question!!
 * Q. Where do you use multicast delegates? 
 * A. Multicast delegates make implementations of observer design patterns simple. (Observer pattern design is also called publish/subscribe pattern)
 * 
 */


//APPROACH ONE
/*
public delegate void SampleDelegate();

public class Program
{
    public static void Main()
    {
        SampleDelegate del1, del2, del3, del4;
        del1 = new SampleDelegate(SampleMethodOne);
        del2 = new SampleDelegate(SampleMethodTwo);
        del3 = new SampleDelegate(SampleMethodThree);

        del4 = del1 + del2 + del3; //delegate four is now pointing to all three methods
        del4(); //This is our multicast delegate

        Console.ReadKey();
    }

    public static void SampleMethodOne()
    {
        Console.WriteLine("SampleMethodOne invoked");
    }
    public static void SampleMethodTwo()
    {
        Console.WriteLine("SampleMethodTwo invoked");
    }
    public static void SampleMethodThree()
    {
        Console.WriteLine("SampleMethodThree invoked");
    }
    
}
*/

//APPROACH TWO - using the same instance of a delegate to point to multiple methods

public delegate void SampleDelegate(out int integer);

public class Program
{
    public static void Main()
    {
        SampleDelegate del = new SampleDelegate(SampleMethodOne);
        del += SampleMethodTwo;

        int DelegateOutputReturnValue = 0;

        del(out DelegateOutputReturnValue);

        Console.WriteLine("DelegateReturnedValue = {0}", DelegateOutputReturnValue); //if the delegate has an out parameter, the value of the 
                                                                                     //output parameter will be the value assigned by the last invoked method
                                                                                     //in this case, it will return the output of SampleMethodTwo
        Console.ReadKey();
    }

    public static void SampleMethodOne(out int number)
    {
        number = 1;
    }
    public static void SampleMethodTwo(out int number)
    {
        number = 2;
    }

}