What's the better way to addObserver/removeObserver with NSNotificationCenter?

Question

I used to addObserver in viewDidLoad: and removeObserver in dealloc:. Code:

- (void)viewDidLoad {     [super viewDidLoad];      [[NSNotificationCenter defaultCenter] addObserver:self                                              selector:@selector(refreshData)                                                  name:AnyNotification                                                object:nil]; }  - (void)dealloc {     [[NSNotificationCenter defaultCenter] removeObserver:self                                                     name:AnyNotification                                                   object:nil]; } 

But according to some articles said, it's better to addObserver in viewDidAppear: and removeObserver in viewDidDisappear:. Code:

- (void)viewDidAppear:(BOOL)animated {     [super viewDidAppear:animated];      [[NSNotificationCenter defaultCenter] addObserver:self                                              selector:@selector(refreshData)                                                  name:AnyNotification                                                object:nil]; }  - (void)viewDidDisappear:(BOOL)animated {     [super viewDidDisappear:animated];      [[NSNotificationCenter defaultCenter] removeObserver:self                                                     name:AnyNotification                                                   object:nil]; } 

So, what's the better way to addObserver/removeObserver?

Answer 1

this depends on your scenario, usually the best approach is to add in viewDidLoad and remove in dealloc and in viewDidUnload (deprecated in iOS 9.0, use dealloc only), but there are some cases when you have same method in different classes like UI effects and want to call only current screen's method using notification, then you will have to add the observer in viewWillAppear and remove it in viewWillDisappear or viewDidAppear/viewDidDisappear

Edit: A note from comments, thanks @honey.

Though now since iOS 9, you no longer need to care about removing the observer. See Apple release notes: "In OS X 10.11 and iOS 9.0 NSNotificationCenter and NSDistributedNotificationCenter will no longer send notifications to registered observers that may be deallocated..