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Multicast Delegates :: Advance : C# programming for c++ programmers



Defination:

A Multicast delegate is a delegate that has references to more than one function.

 When you call a multicast delegate, all the functions the delegate is pointing to, are invoked.

Example 1:

using System;
namespace demo
{
    public delegate void demoDelegate();
    
    public class demoSample
    {
        static void Main()
        {
            demoDelegate del1 = new demoDelegate(demoMethodOne);
            demoDelegate del2 = new demoDelegate(demoMethodTwo);
            demoDelegate del3 = new demoDelegate(demoMethodThree);
            
            demoDelegate del4 = del1 + del2 + del3 - del3;
            

             del4();  // del4 invokes de1 and del2, since -del3 is invoked, call to del3 is removed.
        }
        public static void demoMethodOne()
        {
            Console.WriteLine("SampleMethodOne Invoked");
        }
        public static void demoMethodTwo()
        {
            Console.WriteLine("SampleMethodTwo Invoked");
        }
        public static void demoMethodThree()
        {
            Console.WriteLine("SampleMethodThree Invoked");
        }
    }
}


Note: 

  • Delegate objects can be composed using the "+" operator.
  • The "-" operator can be used to remove a component delegate from a composed delegate.
  • 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 out parameter, the value of the output parameter, will be the value assigned by the last method.





Example 2: Instead of creating multiple delegate object, we can directly assign method through += and -=.


namespace demo
{
    public delegate void demoDelegate();
    
    public class demoSample
    {
        static void Main()
        {
            demoDelegate del = new demoDelegate(demoMethodOne);
   del += demoMethodTwo;
   del += demoMethodThree;
            del -= demoMethodTwo;
        }
        public static void demoMethodOne()
        {
            Console.WriteLine("SampleMethodOne Invoked");
        }
        public static void demoMethodTwo()
        {
            Console.WriteLine("SampleMethodTwo Invoked");
        }
        public static void demoMethodThree()
        {
            Console.WriteLine("SampleMethodThree Invoked");
        }
    }
}
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