Correct way of using removeObserver in Master/Detail application

Question

In a master-detail application, I have the following layout;

Master Let's assume we have a UITableView here

Detail Shows more information about a item from the Master. We setup a observer in NSNotificationCenter here

DetailModal Shows something, is shown from Detail

Where is the correct way of calling removeObserver if I still want to receive notifications when Detail or DetailModal is shown but remove it when we go back to Master?

The way I see it, I would set a flag to not remove the observer when showing the DetailModal and check for that flag in viewWillDissapear. Is this a good approach?

score 2 · Accepted Answer · edited May 23 '17 at 10:25

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Not dealloc - see this question for a discussion.

It's best to do it in ViewWillDisappear. I usually have a boolean "isObserving" flag that is set when observing starts and then checked when ViewWillDisappear is called.

eta- best practice suggests it should actually be done in both, but the dealloc is only a backstop.

eta#2: With ARC, dealloc is only called when the reference count falls to zero. If it's observing, a reference still exists and so dealloc never gets called.

edited May 23 '17 at 10:25

Community

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answered Sep 06 '13 at 09:00

Will Jenkins

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Sounds like my idea of a flag and check in viewWillDisappear would be the way then. – hank Sep 06 '13 at 09:05
the selected answer in the link you pasted is actually saying to use dealloc – Nimrod Gutman Sep 06 '13 at 09:09
The discussion is spread out over that question, this is perhaps a better link: http://www.cocoabuilder.com/archive/cocoa/311831-arc-and-dealloc.html – Will Jenkins Sep 06 '13 at 09:16

score 0 · Answer 2 · answered Sep 06 '13 at 08:57

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I usually call removeObserver on the - (void)dealloc method of my subview / subview controller. After popping the DetailModal it should be released.

answered Sep 06 '13 at 08:57

Nimrod Gutman

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Correct way of using removeObserver in Master/Detail application

2 Answers2