Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
Assembly: mscorlib (in mscorlib.dll)
Thetype exposes the following members.
|CombineImpl||Combines this Delegate with the specified Delegate to form a new delegate. (Overrides Delegate.CombineImpl(Delegate).)|
|DynamicInvoke||Dynamically invokes (late-bound) the method represented by the current delegate. (Inherited from Delegate.)|
|Equals||Determines whether this multicast delegate and the specified object are equal. (Overrides Delegate.Equals(Object).)|
|Finalize||Allows 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.
|GetHashCode||Returns the hash code for this instance. (Overrides Delegate.GetHashCode.)|
|GetInvocationList||Returns the invocation list of this multicast delegate, in invocation order. (Overrides Delegate.GetInvocationList.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|RemoveImpl||Removes an element from the invocation list of this that is equal to the specified delegate. (Overrides Delegate.RemoveImpl(Delegate).)|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
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 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 class.
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.
' 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
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.