I need to set up user proof time keeping in my current project. I have found a lot of different question around this, but none that seem to have the answer I am looking for. These are the questions i have looked at so far:
XCODE: How to get/verify ACCURATE timestamp from device
Is it possible to get the atomic clock timestamp from the iphone GPS?
How can I get the real time in iPhone, not the time set by user in Settings?
I have several options for getting a time from a server connection but I need to have an offline solution too.
1. It seems that using CLLocation gets the same time as as the device clock. Is there away to get the actual GPS time?
2. I know the system time settings are not a public API thus can't be changed. Is it possible to find out if the device has the auto time setting turned on? If the auto time is on then I can rely on the system time for my purposes and if it's off then record that so I know that the time recorded is not to be trusted?
Just wanted to post my solution, incase some one else has the same issue.
After much research i found that getting GPS time of time setting info was not possible.
This solution isn't perfect nor real time but works for my purpose.
I have implemented a time check using cloud time each time the app comes on line. When the device re-establishes a server connection to sync events created off line i have put a verification that takes the last object device time and the new object device time and calculates the elapsed time between the two. (using NSdates so that daylight savings is covered) then do the same with the last available server time and the most recent server time. I then compare the results and if they are not within my margin of error the events are marked as invalid.
Hope that makes sense and is helpful for others.
来源：https://stackoverflow.com/questions/36232672/check-if-system-time-is-auto-or-user-set