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I would like to observe changes to settings values in [NSUserDefaults standardDefaults]. I am using the InAppSettingsKit to access and change settings in the program. Until now, I have just assumed all values have changed and sent notifications to all observers to update based on new values. This is not efficient and I only want to send notifications to observers when a relevant change has occurred.

Can someone suggest an efficient way to do this?

Can I assume that the value for any key from [NSUserDefaults standardDefaults] is never an array, set, or a dictionary? (Working with settings is new for me. This would probably help if I had to do a brute force scan for changes, comparing a before-dictionary with an after-dictionary. And it would not require any recursion.)

If this is already in the InAppSettingsKit, I haven't seen it, and I would be glad if someone could point it out.

Jim
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  • http://stackoverflow.com/questions/1141388/cocoa-notification-on-nsuserdefaults-value-change – M.Y. May 22 '12 at 11:16

2 Answers2

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There is no system notification that holds the details of which default value was changed. I can't speak for inappsettings kit as I have not used it.

Your individual objects that are responding to the changes should hold local values for their relevant default settings and only perform expensive operations if necessary. Therefore responding to the notification should be a simple operation. If you have two separate objects that respond to different sub-objects within a single dafaults key then you may want to re-think how your defaults are organised. If you've got some specific examples please include them in your question.

Before rewriting your whole app to have some sort of defaults manager object in the name of "efficiency" do test to make sure that you are actually wasting significant, user-experience impacting amounts of time having lots of objects respond to the notification, otherwise you are optimising prematurely and you know what they say about that.

In answer to the second part of your question, you can't make that assumption. Any property list objects can be stored in user defaults.

jrturton
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  • I'm going to take your advice. There are a handful of settings that affect the predicates used for searches and the data displayed. I'll assume only these have changed and fire a notification that can get them updated before the settings panel is dismissed (so the user doesn't notice the changes as they are occurring). I'll check for changes to other settings the lazy way. – Jim Nov 06 '11 at 16:54
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    +1 for "test to make sure that you are actually wasting significant, user-experience impacting amounts of time". Too much code written in the name of "performance" should never have been written, especially on iOS. It should be noted, however, that even if the user doesn't notice performance problems, their battery might ;) – Chris McCall Oct 24 '12 at 14:51
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Binding is not yet available in iOS.

jemeshsu
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