MulticastDelegate Class
Assembly: mscorlib (in mscorlib.dll)
'Declaration <SerializableAttribute> _ <ComVisibleAttribute(True)> _ Public MustInherit Class MulticastDelegate Inherits Delegate 'Usage Dim instance As MulticastDelegate
/** @attribute SerializableAttribute() */ /** @attribute ComVisibleAttribute(true) */ public abstract class MulticastDelegate extends Delegate
SerializableAttribute ComVisibleAttribute(true) public abstract class MulticastDelegate extends Delegate
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.
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 a class that is derived from MulticastDelegate.
Imports System Imports Microsoft.VisualBasic ' This class contains strings. It has a member method that ' accepts a multicast delegate as a parameter and calls it Class HoldsStrings ' The following line causes the compiler to generate ' a new delegate class named CheckAndPrintDelegate that ' inherits from System.MulticastDelegate. Delegate Sub CheckAndPrintDelegate(ByVal str As String) ' An ArrayList that holds strings Private myStringArray As New System.Collections.ArrayList() Public Sub addstring(ByVal str As String) myStringArray.Add(str) End Sub 'addstring ' Iterate through the strings and invoke the method(s) that the delegate points to Public Sub PrintAllQualified(ByVal myDelegate As CheckAndPrintDelegate) Dim str As String For Each str In myStringArray myDelegate(str) Next str End Sub 'PrintAllQualified End Class 'end of class HoldsStrings ' This class contains a few sample methods Class StringFuncs ' This method prints a string that it is passed if the string starts with a vowel Public Shared Sub ConStart(ByVal str As String) If Not (str.Chars(0) = "a"c Or str.Chars(0) = "e"c Or str.Chars(0) = "i"c Or str.Chars(0) = "o"c Or str.Chars(0) = "u"c) Then Console.WriteLine(str) End If End Sub 'ConStart ' This method prints a string that it is passed if the string starts with a consonant Public Shared Sub VowelStart(ByVal str As String) If (str.Chars(0) = "a"c Or str.Chars(0) = "e"c Or str.Chars(0) = "i"c Or str.Chars(0) = "o"c Or str.Chars(0) = "u"c) Then Console.WriteLine(str) End If End Sub 'VowelStart End Class 'StringFuncs ' This class demonstrates using Delegates, including using the Remove and ' Combine methods to create and modify delegate combinations. Class Test Public Shared Sub Main() ' Declare the HoldsStrings class and add some strings Dim myHoldsStrings As New HoldsStrings() myHoldsStrings.addstring("this") myHoldsStrings.addstring("is") myHoldsStrings.addstring("a") myHoldsStrings.addstring("multicast") myHoldsStrings.addstring("delegate") myHoldsStrings.addstring("example") ' Create two delegates individually using different methods Dim ConStartDel = New HoldsStrings.CheckAndPrintDelegate(AddressOf StringFuncs.ConStart) Dim VowStartDel As New HoldsStrings.CheckAndPrintDelegate(AddressOf StringFuncs.VowelStart) ' Demonstrate that MulticastDelegates may store only one delegate Dim DelegateList() As [Delegate] ' Returns an array of all delegates stored in the linked list of the ' MulticastDelegate. In these cases the lists will hold only one (Multicast) delegate DelegateList = ConStartDel.GetInvocationList() Console.WriteLine("ConStartDel contains " + DelegateList.Length.ToString() + " delegate(s).") DelegateList = VowStartDel.GetInvocationList() Console.WriteLine(("ConStartVow contains " + DelegateList.Length.ToString() + " delegate(s).")) ' Determine whether the delegates are System.Multicast delegates If TypeOf ConStartDel Is System.MulticastDelegate And TypeOf VowStartDel Is System.MulticastDelegate Then Console.WriteLine("ConStartDel and ConStartVow are System.MulticastDelegates") End If ' Run the two single delegates one after the other Console.WriteLine("Running ConStartDel delegate:") myHoldsStrings.PrintAllQualified(ConStartDel) Console.WriteLine("Running VowStartDel delegate:") myHoldsStrings.PrintAllQualified(VowStartDel) ' Create a new, empty MulticastDelegate Dim MultiDel As HoldsStrings.CheckAndPrintDelegate ' Delegate.Combine receives an unspecified number of MulticastDelegates as parameters MultiDel = CType([Delegate].Combine(ConStartDel, VowStartDel), HoldsStrings.CheckAndPrintDelegate) ' How many delegates is this delegate holding? DelegateList = MultiDel.GetInvocationList() Console.WriteLine((ControlChars.Cr + "MulitDel contains " + DelegateList.Length.ToString() + " delegates.")) ' What happens when this mulitcast delegate is passed to PrintAllQualified Console.WriteLine("Running the multiple delegate that combined the first two") myHoldsStrings.PrintAllQualified(MultiDel) ' The Remove and Combine methods modify the multiple delegate MultiDel = CType([Delegate].Remove(MultiDel, VowStartDel), HoldsStrings.CheckAndPrintDelegate) MultiDel = CType([Delegate].Combine(MultiDel, ConStartDel), HoldsStrings.CheckAndPrintDelegate) ' Finally, pass the combined delegates to PrintAllQualified again Console.WriteLine(ControlChars.Cr + "Running the multiple delegate that contains two copies of ConStartDel:") myHoldsStrings.PrintAllQualified(MultiDel) Return End Sub 'end of main End Class 'end of Test
import System.*;
// This class contains strings. It has a member method that
// accepts a multicast delegate as a parameter and calls it.
class HoldsStrings
{
/** @delegate
*/
// This delegate is declared as a void, so the compiler automatically
// generates a new class, named CheckAndPrintDelegate, that inherits from
// System.MulticastDelegate.
public delegate void CheckAndPrintDelegate(String str);
// An ArrayList that holds strings
private System.Collections.ArrayList myStringArray =
new System.Collections.ArrayList();
// A method that adds more strings to the Collection
public void addstring(String str)
{
myStringArray.Add(str);
} //addstring
// Iterate through the strings and invoke the method(s) that the delegate
// points to
public void PrintAllQualified(CheckAndPrintDelegate myDelegate)
{
for (int iCtr1 = 0; iCtr1 < myStringArray.get_Count(); iCtr1++) {
String str = System.Convert.ToString(myStringArray.get_Item(iCtr1));
myDelegate.Invoke(str);
}
} //PrintAllQualified
} //HoldsStrings
//end of class HoldsStrings
// This class contains a few sample methods
class StringFuncs
{
// This method prints a string that it is passed if the string starts
// with a vowel
public static void ConStart(String str)
{
if (!(str.get_Chars(0) == 'a' || str.get_Chars(0) == 'e'
|| str.get_Chars(0) == 'i' || str.get_Chars(0) == 'o'
|| str.get_Chars(0) == 'u')) {
Console.WriteLine(str);
}
} //ConStart
// This method prints a string that it is passed if the string starts with
// a consonant
public static void VowelStart(String str)
{
if (str.get_Chars(0) == 'a' || str.get_Chars(0) == 'e'
|| str.get_Chars(0) == 'i' || str.get_Chars(0) == 'o'
|| str.get_Chars(0) == 'u') {
Console.WriteLine(str);
}
} //VowelStart
} //StringFuncs
// This class demonstrates using Delegates, including using the Remove and
// Combine methods to create and modify delegate combinations.
class Test
{
public static void main(String[] args)
{
// Declare the HoldsStrings class and add some strings
HoldsStrings myHoldsStrings = new HoldsStrings();
myHoldsStrings.addstring("This");
myHoldsStrings.addstring("is");
myHoldsStrings.addstring("a");
myHoldsStrings.addstring("multicast");
myHoldsStrings.addstring("delegate");
myHoldsStrings.addstring("example");
// Create two delegates individually using different methods
HoldsStrings.CheckAndPrintDelegate ConStartDel =
new HoldsStrings.CheckAndPrintDelegate(StringFuncs.ConStart);
HoldsStrings.CheckAndPrintDelegate VowStartDel =
new HoldsStrings.CheckAndPrintDelegate(StringFuncs.VowelStart);
// Demonstrate that MulticastDelegates may store only one delegate
Delegate DelegateList[];
// Returns an array of all delegates stored in the linked list of the
// MulticastDelegate. In these cases the lists will hold only one
// (Multicast) delegate
DelegateList = ConStartDel.GetInvocationList();
Console.WriteLine("ConStartDel contains " + DelegateList.get_Length()
+ " delegate(s).");
DelegateList = VowStartDel.GetInvocationList();
Console.WriteLine("ConStartVow contains " + DelegateList.get_Length()
+ " delegate(s).");
// Determine whether the delegates are System.Multicast delegates
// if (ConStartDel is System.MulticastDelegate && VowStartDel is
// System.MulticastDelegate) {
Console.WriteLine("ConStartDel and ConStartVow are "
+ "System.MulticastDelegates");
// }
// Run the two single delegates one after the other
Console.WriteLine("Running ConStartDel delegate:");
myHoldsStrings.PrintAllQualified(ConStartDel);
Console.WriteLine("Running VowStartDel delegate:");
myHoldsStrings.PrintAllQualified(VowStartDel);
// Create a new, empty MulticastDelegate
HoldsStrings.CheckAndPrintDelegate multiDel;
// Delegate.Combine receives an unspecified number of MulticastDelegates
// as parameters
multiDel = (HoldsStrings.CheckAndPrintDelegate)(Delegate.Combine(
ConStartDel, VowStartDel));
// How many delegates is this delegate holding?
DelegateList = multiDel.GetInvocationList();
Console.WriteLine("\nMulitDel contains " + DelegateList.get_Length()
+ " delegates.");
// What happens when this mulitcast delegate is passed to
// PrintAllQualified
Console.WriteLine("Running the multiple delegate that combined the "
+ "first two");
myHoldsStrings.PrintAllQualified(multiDel);
// The Remove and Combine methods modify the multiple delegate
multiDel = (HoldsStrings.CheckAndPrintDelegate)(Delegate.Remove(
multiDel, VowStartDel));
multiDel = (HoldsStrings.CheckAndPrintDelegate)(Delegate.Combine(
multiDel, ConStartDel));
// Finally, pass the combined delegates to PrintAllQualified again
Console.WriteLine("\nRunning the multiple delegate that contains two "
+ "copies of ConStartDel:");
myHoldsStrings.PrintAllQualified(multiDel);
return;
} //main
} //Test
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.