When checking if an event handler is null, is this done on a per-thread basis?
Ensuring someone is listening to the event is done like this:
EventSeven += new DivBySevenHandler(dbsl.ShowOnScreen);
If I add code following this pattern above where I check for null, then why would I need a null check (code taken from this site). What am I missing?
Also, what's the rule with events and GC?
If you mean this:
public static void OnEventSeven(DivBySevenEventArgs e)
{
if(EventSeven!=null)
EventSeven(new object(),e);
}
piece of code, then the answer is:
If nobody subscribes to the "EventSeven" event handler then you'll get a null-reference exception on "EventSeven(new object(),e);"
And the rule:
The subscriber is responsible for adding a handler (+=) and removing it (-=) when he doesn't want to receive the events any longer. Garbage collection goes by the default rules, if an object is no longer referenced it can be cleaned.