I had previously written that a delegate is a class containing a reference to a method. A delegate can actually contain a reference to multiple methods ( which can be in different classes ). When a delegate contains multiple targets, this is called a delegate chain. Typically you would only chain when the return type on the delegate is void.
How do I create a delegate chain ?
You do this by adding the target method to the invocation list of the delegate using += ( compiler syntactic sugar ). In the example below, I’m going to add 3 methods to my delegate:
Can I invoke the same delegate more than once in my chain ?
Yes, simply add it again using the += construct. In the example below, I add the method Foo twice.
How do I remove a delegate item from my chain ?
Use the -= construct to remove a delegate from the chain. Removal operates on a LIFO basis ( last in first out )
What do += and -= actually do ?
Each delegate object holds a collection of the target/methods it is supposed to call. This is called the “invocation list”. With +=, you are adding to the collection. With -= you are removing from the collection
+= calls the Combine method of the static delegate class. As delegates are immutable, the call to the static Combine method creates a new delegate chain and the reference is refreshed to point to this new object heap
-= calls the Remove method of the static delegate class. As delegates are immutable, the call to the static Remove method creates a new delegate chain and the reference is refreshed to point to this new object heap
C#/SQL Notes 
Leave a comment