Multicast Deletages (Multicasting)

Multicasting is the ability to create an invocation list, or chain, of methods that will be automatically called when a delegate is invoked.

Steps:

• Instantiate a delegate
• use the + or += operator to add methods to the chain
• use the – or –= operator to remove methods from the chain 

If the delegate returns a value, then the value returned by the last method in the list becomes the return value of the entire delegate invocation. 

Example:

// Multicasting Demo
using System;

// Declare a delegate type

delegate void ModifyString(ref string sTestString);

class MultiCastDemo

{

  // Replaces spaces with dollars

  static void ReplaceSpaces(ref string sTestString)

  { 

    sTestString = sTestString.Replace(' ', '$');

    Console.WriteLine("Replaced spaces with dollars.");

  }

  // Remove spaces

  static void RemoveSpaces(ref string sTestString)

  {

    string temp = "";

    int i;

    for(i=0; i < sTestString.Length; i++)

      if(sTestString[i] != ' ') temp += sTestString[i];

    sTestString = temp;

    Console.WriteLine("Removed spaces.");

  }

  // Reverse a string

  static void Reverse(ref string sTestString)

  {

    string temp = "";

    int i, j;

    for(j=0, i= sTestString.Length-1; i >= 0; i--, j++)

      temp += sTestString[i];

    sTestString = temp;

    Console.WriteLine("Reversed string.");

  }

  static void Main()

  {

    // Construct delegates

    ModifyString oModifyString;

    ModifyString oModifyStringReplaceSpaces = ReplaceSpaces;  // Method Group Conversion

    ModifyString oModifyStringRemoveSpaces = RemoveSpaces;  // Method Group Conversion

    ModifyString oModifyStringReverseString = Reverse;  // Method Group Conversion

    string sString = "This is a test for Multicast Delegates";

   

    // Set up multicast

    oModifyString = oModifyStringReplaceSpaces;

    oModifyString += oModifyStringReverseString;

   

    // Call multicast

    oModifyString(ref sString);

    Console.WriteLine("Resulting string: " + sString);

    Console.WriteLine();

   

    // Remove replace and add remove

    oModifyString -= oModifyStringReplaceSpaces;

    oModifyString += oModifyStringRemoveSpaces;

    sString = "This is a test."; // reset string

   

    // Call multicast

    oModifyString(ref sString);

    Console.WriteLine("Resulting string: " + sString);

    Console.WriteLine();

  }

}

Related Post: Delegates