UserDefaults in IOS 10 is sometimes showing old value

Question

I am testing something on my app where I save the current used theme as a string: "Light" vs "Dark".

I just realized that at some point when I keep switching from light to dark (reading and writing the string to UserDefaults) I sometimes get on old value:

Light -> Dark -> Light -> Dark -> Light -> Light

I have added logs to where I read and write the value and its doing it correctly. This is how I test:

 1. Start app 
 2. Change theme (save string to UserDefaults)
 3. Stop app
 4. Start app (read string from UserDefaults)

I saw some other posts which says there is a problem with UserDefaults in IOS 10 and the solution is to restart device or mac.

I get this, but doesn't this mean the issue will appear on the user device as well ? Has anyone encounter this kind of issue ? Any solution ?

I am using Xcode 8.2.1 with IOS 10, Swift 3. And I am testing on my real device, not simulator.

Are you sure the value does write itself into userdefalts? I mean, you can try the syncronize thing. They doesn't recommend it however for me it seems like it don't write the value so fast into disk. — Tarvo Mäesepp, Feb 11 '17 at 10:21
I did some more testing and I just realized that this issue occurs when I restart quickly, right after the item is saving. If I pause for two seconds, it seems I don't have the issue. — Adrian, Feb 11 '17 at 10:36
Then my solution is for you. Use syncronize to immediately save the value. — Tarvo Mäesepp, Feb 11 '17 at 11:00
'.synchronise()' returns a bool which indicates whether it was saved — saurabh, Feb 11 '17 at 11:51

score 3 · Accepted Answer · answered Feb 11 '17 at 11:25

3

Are you sure that you call [[NSUserDefaults standardUserDefaults] synchronize]; after saving Data?

answered Feb 11 '17 at 11:25

Chris8447

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UserDefaults in IOS 10 is sometimes showing old value

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