问题
The gods have parachuted many habits into my isolated jungle village, such as:
- (void) dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
[super dealloc];
}
Their ways are strange to me, yet I still seek to understand them.
Why bother cleaning loose ends up if the instance is going away? Will the reference/retain count to that instance not be decremented? Will it clutter some sort of Notification Hash Table lurking out there that holds a list of all the listeners?
回答1:
NSNotificationCenter doesn't retain observers. If you don't remove the observer, and the observer is deallocated, then NSNotificationCenter is left holding a dangling pointer which will (most often) crash when it next tries to notify the observer.
回答2:
Although in practice many of your uninitiated younglings will get away without following the rites, because it has pleased St. Jobs to bestow a removeObserver incantation upon many of your super classes. Such as UINavigationController. Although this is not found in any the Writings I have found this to be true.
来源：https://stackoverflow.com/questions/3964041/nsnotificationcenter-why-bother-calling-removeobserver