Question

I am confused by the syntax for removing event handlers in C#.

Something += new MyHandler(HandleSomething); // add
Something -= new MyHandler(HandleSomething); // remove

The “new” creates a new object on each line, so you add one object
and then ask it to remove a different object.

What is really going on under the covers that this can work?
It sure isn’t obvious from the syntax.

Answer 1

The += and the -= are syntax shortcuts for built-in internal methods named Add(), and Remove(), which add or remove a pointer to an internal linked list of delegates that the delegate has as a private field. When you run Remove, it starts at the head of the linked list and examines each delegate in the list one at a time until it finds one that is “equal” to the one you passed to the Remove() method. ( using -= syntax)

Then, it removes that one from the linked list, and patches the linked list to retain it’s connectivity…

In this context, the ‘equals’ method (for a delegate()) is overridden so that it only compares the target of the delegate, and the methodPtr, which will be the same even though you have created a new delegate to pass to Remove…