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MulticastDelegate Class

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)

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class MulticastDelegate _
	Inherits Delegate

The MulticastDelegate type exposes the following members.

  NameDescription
Protected methodMulticastDelegateInitializes a new instance of the MulticastDelegate class.
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  NameDescription
Public propertySupported by Silverlight for Windows PhoneSupported by Xbox 360MethodGets the method represented by the delegate. (Inherited from Delegate.)
Public propertySupported by Silverlight for Windows PhoneSupported by Xbox 360TargetGets the class instance on which the current delegate invokes the instance method. (Inherited from Delegate.)
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  NameDescription
Protected methodSupported by Silverlight for Windows PhoneSupported by Xbox 360CombineImplCombines this Delegate with the specified Delegate to form a new delegate. (Overrides Delegate.CombineImpl(Delegate).)
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360DynamicInvokeDynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate.)
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360EqualsDetermines whether this multicast delegate and the specified object are equal. (Overrides Delegate.Equals(Object).)
Protected methodSupported by Silverlight for Windows PhoneSupported by Xbox 360FinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)

In Silverlight for Windows Phone, this member is overridden by Finalize.


In XNA Framework, this member is overridden by Finalize.
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360GetHashCodeReturns the hash code for this instance. (Overrides Delegate.GetHashCode.)
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360GetInvocationListReturns the invocation list of this multicast delegate, in invocation order. (Overrides Delegate.GetInvocationList.)
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360GetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodSupported by Silverlight for Windows PhoneSupported by Xbox 360MemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodSupported by Silverlight for Windows PhoneSupported by Xbox 360RemoveImplRemoves an element from the invocation list of this MulticastDelegate that is equal to the specified delegate. (Overrides Delegate.RemoveImpl(Delegate).)
Public methodSupported by Silverlight for Windows PhoneSupported by Xbox 360ToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Public operatorStatic memberSupported by Silverlight for Windows PhoneSupported by Xbox 360EqualityDetermines whether two MulticastDelegate objects are equal.
Public operatorStatic memberSupported by Silverlight for Windows PhoneSupported by Xbox 360InequalityDetermines whether two MulticastDelegate objects are not equal.
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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.

In Silverlight, 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.


' Declare a delegate class named CheckAndPrintDelegate that takes a
' string. All delegates derive from System.MulticastDelegate.
Delegate Sub CheckAndPrintDelegate(ByVal str As String)

' This class demonstrates using Delegates, including using the Remove and
' Combine methods to create and modify delegate combinations. 
'
Class Example

   Private Shared outputBlock As System.Windows.Controls.TextBlock

   ' A List that holds strings.
   Private Shared strList As New System.Collections.Generic.List(Of String)

   ' Iterate through the strings and invoke the method(s) that the delegate 
   ' represents.
   Public Shared Sub PrintAllQualified(ByVal myDelegate As CheckAndPrintDelegate)
      For Each str As String In strList
         myDelegate(str)
      Next str
   End Sub 

   ' This method prints the string that is passed to it if the string 
   ' starts with a consonant.
   Public Shared Sub ConStart(ByVal str As String)
      If "aeiou".IndexOf(str.Chars(0)) < 0 Then 
         outputBlock.Text &= str & vbLf
      End If
   End Sub 

   ' This method prints the string that is passed to it if the string
   ' starts with a vowel.
   Public Shared Sub VowelStart(ByVal str As String)
      If "aeiou".IndexOf(str.Chars(0)) > -1 Then 
         outputBlock.Text &= str & vbLf
      End If
   End Sub 

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      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.
      Dim ConStartDel As New CheckAndPrintDelegate(AddressOf Example.ConStart)

      Dim VowStartDel As New CheckAndPrintDelegate(AddressOf 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)." & vbLf

      outputBlock.Text &= "VowStartDel contains " & _
         VowStartDel.GetInvocationList().Length & " delegate(s)." & vbLf

      ' Determine whether the delegates are System.Multicast delegates
      If TypeOf ConStartDel Is System.MulticastDelegate And _
         TypeOf VowStartDel Is System.MulticastDelegate Then

         outputBlock.Text &= "ConStartDel and VowStartDel are System.MulticastDelegate." & vbLf
      End If

      ' Run the two single delegates one after the other.
      outputBlock.Text &= "Using ConStartDel delegate:" & vbLf
      PrintAllQualified(ConStartDel)

      outputBlock.Text &= vbLf & "Using VowStartDel delegate:" & vbLf
      PrintAllQualified(VowStartDel)

      ' Delegate.Combine receives a list of MulticastDelegates as parameters 
      ' and combines their invocation lists in a new Multicast delegate.
      Dim MultiDel As CheckAndPrintDelegate = _
         CType([Delegate].Combine(ConStartDel, VowStartDel), CheckAndPrintDelegate)

      ' How many delegates is this delegate holding?
      outputBlock.Text &= vbLf & "MultiDel contains " & _
         MultiDel.GetInvocationList().Length & " delegates." & vbLf

      ' What happens when this mulitcast delegate is passed to 
      ' PrintAllQualified?
      outputBlock.Text &= "Using the Multicast delegate that combines ConStartDel and VowStartDel:" & vbLf
      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 = CType([Delegate].Remove(MultiDel, VowStartDel), CheckAndPrintDelegate)
      MultiDel = CType([Delegate].Combine(MultiDel, ConStartDel), CheckAndPrintDelegate)

      ' Pass the new Multicast delegate to PrintAllQualified.
      outputBlock.Text &= vbLf & "Using the Multicast delegate that contains two copies of ConStartDel:" & vbLf
      PrintAllQualified(MultiDel)

   End Sub 
End Class 

' 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


Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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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