When is it useful to have multicast delegates over singlecast delegates?
I use delegates a lot, mainly coupled with C# lambdas, but I've never felt the urge to use the multicast aspect of C# delegates, ie I've never wanted to combine multiple delegates together in a single delegate. I'm therefore very curious in what sort of situation multicast delegates are useful - I can only think of examples in which you can easily implement the functionality some other way, by, say, chaining the delegates or putting them in a list.
In particular, Eric Lippert's answer here gives the impression even the C# team sometimes forgets about the multicastiness of delegates.
Anything acting as an event is the classic answer here - then the caller doesn't need to know who is listening (just invoke it, if it is non-null). This is ideal as multiple operations can subscribe simultaneously - for example 3 separate controls observing (data-binding) to the same property on a view-model.
Any cases where the delegate is acting as function (in particular with a return value) is tricker, as you need to think how you will handle that - take the first? Last? Aggregate?
Events are a prime example for the usage of MulticastDelegates. So, probably without realizing it, you are using them every day.
来源：https://stackoverflow.com/questions/6297550/use-of-multicast-in-c-sharp-multicast-delegates