how does PropertyChangedEventHandler work?

Question

This is a really simple question, but I was wondering if someone could explain what the 4th line is actually doing? so the first line gives an event to the handler. I don\'t

Answer 1

PropertyChanged is the event that was declared like this, according to its definition in the interface:

public event PropertyChangedEventHandler PropertyChanged;

Events that are defined like that are actually a syntactic sugar for a list of event handlers you can add a delegate (that is a reference to a function) to by subscribing, or remove a delegate by unsubscribing.

Now, when you call an event, i.e. PropertyChanged(...), then what happens internally is that every delegate in that internal list is called separately with the parameters. This will tell all the subscribers of your event that the event happened.

Now, the reason for the whole thing with the handler variable is, that PropertyChanged can be null. If nothing subscribed to it, then calling the event (or rather the event handler list) would not work, so this is just a way to ensure that you can actually execute the handler.