Failed to read values in CFPrefsPlistSource iOS 10
This is actually a spurious warning that was introduced in iOS 10 and macOS 10.12:
NSUserDefaults tip: in the current OSs there's a logged error "…with a container is only allowed for System Containers…".
This is spurious.
Trying to catch a particular failure mode, caught a normal operation case at the same time.
My successor on UserDefaults also has not figured out a way to make this less alarming without making the symptomatic case impossible to debug :/
https://twitter.com/Catfish_Man/status/784460565972332544 [thread]
The advice of prepending your team ID will silence the warning, but will also create a new empty user defaults. This will result in any previously stored data being unreadable.
For the time being, the solution is just to ignore it.
Also, Apple staff member CFM on the forums:
The logged message is spurious unless you're doing very specific things that I don't think are possible without using private functions (it was added to catch misuse of those functions, but unfortunately also caught a normal usage case).
NSUserDefaults errors in logs
Lot of people are finding this issue on Xcode 8.
"As crazy as it sounds try rebooting phone and host, sometimes Xcode can get stuck for sum reason only restart helps.
build with Xcode 8.1 Beta and you will see the same warning, but you will also get the value. "
reference : https://forums.developer.apple.com/thread/51348
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