MulticastDelegate Class

May 11, 2014

Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.

System.Object
  System.Delegate
    System.MulticastDelegate

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public abstract class MulticastDelegate : Delegate

The MulticastDelegate type exposes the following members.

  NameDescription
Public propertyMethodGets the method represented by the delegate. (Inherited from Delegate.)
Public propertyTargetGets the class instance on which the current delegate invokes the instance method. (Inherited from Delegate.)
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  NameDescription
Protected methodCombineImplCombines this Delegate with the specified Delegate to form a new delegate. (Overrides Delegate.CombineImpl(Delegate).)
Public methodDynamicInvokeDynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate.)
Public methodEqualsDetermines whether this multicast delegate and the specified object are equal. (Overrides Delegate.Equals(Object).)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeReturns the hash code for this instance. (Overrides Delegate.GetHashCode().)
Public methodGetInvocationListReturns the invocation list of this multicast delegate, in invocation order. (Overrides Delegate.GetInvocationList().)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodRemoveImplRemoves an element from the invocation list of this MulticastDelegate that is equal to the specified delegate. (Overrides Delegate.RemoveImpl(Delegate).)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Public operatorStatic memberEqualityDetermines whether two MulticastDelegate objects are equal.
Public operatorStatic memberInequalityDetermines whether two MulticastDelegate objects are not equal.
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  NameDescription
Public Extension MethodGetMethodInfoGets an object that represents the method represented by the specified delegate. (Defined by RuntimeReflectionExtensions.)
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MulticastDelegate is a special class. Compilers and other tools can derive from this class, but you cannot derive from it explicitly. The same is true of the Delegate class.

Using delegates to make asynchronous method calls is not supported. Calling BeginInvoke causes a NotSupportedException.

A MulticastDelegate has a linked list of delegates, called an invocation list, consisting of one or more elements. When a multicast delegate is invoked, the delegates in the invocation list are called synchronously in the order in which they appear. If an error occurs during execution of the list then an exception is thrown.

The following example demonstrates the use of the MulticastDelegate class.


using System;

// Declare a delegate class named CheckAndPrintDelegate that takes a
// string. All delegates derive from System.MulticastDelegate.
public delegate void CheckAndPrintDelegate(string str);

// This class demonstrates using Delegates, including using the Remove and
// Combine methods to create and modify delegate combinations. 
//
class Example
{
   private static System.Windows.Controls.TextBlock outputBlock;

   // A List that holds strings.
   private static System.Collections.Generic.List<string> strList = 
      new System.Collections.Generic.List<string>();

   // Iterate through the strings and invoke the method(s) that the delegate 
   // represents.
   public static void PrintAllQualified(CheckAndPrintDelegate myDelegate)
   {
      foreach (string str in strList)
      {
         myDelegate(str);
      }
   }

   // This method prints the string that is passed to it if the string 
   // starts with a consonant.
   public static void ConStart(string str)
   {
      if ("aeiou".IndexOf(str[0]) < 0)
         outputBlock.Text += str + "\n";
   }

   // This method prints the string that is passed to it if the string
   // starts with a vowel.
   public static void VowelStart(string str)
   {
      if ("aeiou".IndexOf(str[0]) > -1)
         outputBlock.Text += str + "\n";
   }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Example.outputBlock = outputBlock;

      strList.Add("this");
      strList.Add("is");
      strList.Add("a");
      strList.Add("multicast");
      strList.Add("delegate");
      strList.Add("example");

      // Create two delegates individually.
      CheckAndPrintDelegate ConStartDel =
          new CheckAndPrintDelegate(Example.ConStart);

      CheckAndPrintDelegate VowStartDel =
          new CheckAndPrintDelegate(Example.VowelStart);

      // GetInvocationList() returns an array of all delegates stored in the 
      // linked list of the MulticastDelegate. In these cases the lists will 
      // hold only one delegate.
      outputBlock.Text += "ConStartDel contains " + 
         ConStartDel.GetInvocationList().Length + " delegate(s)." + "\n";
      outputBlock.Text += "VowStartDel contains " + 
         VowStartDel.GetInvocationList().Length + " delegate(s)." + "\n";

      // Determine whether the delegates are System.Multicast delegates
      if (ConStartDel is System.MulticastDelegate && 
          VowStartDel is System.MulticastDelegate) 
      {
         outputBlock.Text += "ConStartDel and VowStartDel are System.MulticastDelegate." + "\n";
      }

      // Run the two single delegates one after the other.
      outputBlock.Text += "Using ConStartDel delegate:\n";
      PrintAllQualified(ConStartDel);

      outputBlock.Text += "\nUsing VowStartDel delegate:\n";
      PrintAllQualified(VowStartDel);

      // Delegate.Combine receives a list of MulticastDelegates as parameters 
      // and combines their invocation lists in a new Multicast delegate.
      CheckAndPrintDelegate MultiDel =
         (CheckAndPrintDelegate)Delegate.Combine(ConStartDel, VowStartDel);

      // How many delegates is this delegate holding?
      outputBlock.Text += "\nMultiDel contains " + 
         MultiDel.GetInvocationList().Length + " delegates." + "\n";

      // What happens when this mulitcast delegate is passed to 
      // PrintAllQualified?
      outputBlock.Text += "Using the Multicast delegate that combines ConStartDel and VowStartDel:" + "\n";
      PrintAllQualified(MultiDel);

      // The Remove and Combine methods create new Multicast delegates with
      // the specified delegates removed from or combined with the existing
      // invocation list. 
      MultiDel = (CheckAndPrintDelegate)Delegate.Remove(MultiDel, VowStartDel);
      MultiDel = (CheckAndPrintDelegate)Delegate.Combine(MultiDel, ConStartDel);

      // Pass the new Multicast delegate to PrintAllQualified.
      outputBlock.Text += "\nUsing the Multicast delegate that contains two copies of ConStartDel:" + "\n";
      PrintAllQualified(MultiDel);
   }  
}   

/* This example produces the following output:

ConStartDel contains 1 delegate(s).
VowStartDel contains 1 delegate(s).
ConStartDel and VowStartDel are System.MulticastDelegate.
Using ConStartDel delegate:
this
multicast
delegate

Using VowStartDel delegate:
is
a
example

Using the Multicast delegate that combines ConStartDel and VowStartDel:
this
is
a
multicast
delegate
example

Using the Multicast delegate that contains two copies of ConStartDel:
this
this
multicast
multicast
delegate
delegate
 */


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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