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New Message on BDOTNET
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From: Akshit56491
Message 2 in Discussion
Hi Koduri, The .NET Framework distinguishes between two kinds of delegates, those
with multiple associated functions, referred to as multicast delegates, and those with
only a single associated function, called single-cast delegates. With a multicast
delegate, the .NET Framework internally builds a linked list of function pointers and
calls each of them in turn when the delegate is invoked. Methods are added to the
internal list via the Delegate class�s Combine method, which in C# is mapped to the +=
construct. To remove a method from a delegate�s invocation list, use the Remove
method, or in C#, the -= operator.
Thus, to extend our original example a bit further, if a second class method,
NotifyMeToo, also needs notification when Notifier finishes its work, you could use
code like that found in Listing D. When NotifyDelegate is invoked, Caller.Notify and
Caller.NotifyMeToo are each invoked in turn.
I should point out that the multiple methods in a delegate�s invocation list need not
be on the same object instance or even declared as part of the same class. So in this
case, NotifyMeToo doesn�t necessarily have to be a method on the same instance of
Caller and could even be declared on a separate class from the original Notify method.
Also, bear in mind this (hopefully) rather obvious point: Two different instances of
Notify will have two different internal instances of NotifyDelegate. An invocation of
one will not result in the calling of methods registered on the other.
Finally, a couple of rules govern what can and can't be a multicast delegate:
� The return type of the delegate must be void (a sub in VB.NET).
� The parameter list must not include any out parameters (byRef for VB.NET).
If these two rules are not met, any attempt to add a function to a delegate�s
invocation list will result in a compile-time error.
Regards, Akshit
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