What To Do Now?
It has just come to light that the UIDevice uniqueIdentifier property is deprecated in iOS5 and above. No alternative method or property appears to be available or forthcoming.
Many of our existing apps are tightly dependent on this property for uniquely identifying a particular device. Can anyone suggest any ideas how we might handle this problem going forward?
The suggestion from the documentation is...
Special Considerations
Do not use the uniqueIdentifier property. To create a unique identifier specific to your app, you can call the CFUUIDCreate function to create a UUID , and write it to the defaults database using the NSUserDefaults class.
However this value won't be the same if a user uninstalls and re-installs the app.
A UUID created by CFUUIDCreate is unique if a user uninstalls and re-installs the app: you will get a new one each time.
But you might want it to be not unique, ie it should stay the same when the user uninstalls and re-installs the app. This requires a bit of effort, since the most reliable per-device-identifier seems to be the MAC address. You could query the MAC and use that as UUID.
Edit: One needs to always query the MAC of the same interface, of course. I guess the best bet is with en0 . The MAC is always present, even if the interface has no IP/is down.
Edit 2: As was pointed out by others, the preferred solution since iOS 6 is -[UIDevice identifierForVendor]. In most cases, you should be able use it as a drop-in replacement to the old -[UIDevice uniqueIdentifier] (but a UUID that is created when the app starts for the first time is what Apple seems to want you to use).
Edit 3: So this major point doesn't get lost in the comment noise: do not use the MAC as UUID, create a hash using the MAC. That hash will always create the same result every time, even across reinstalls and apps (if the hashing is done in the same way). Anyways, nowadays (2013) this isn't necessary any more except if you need a "stable" device identifier on iOS < 6.0.
Edit 4: In iOS 7, Apple now always returns a fixed value when querying the MAC to specifically thwart the MAC as base for an ID scheme. So you now really should use -[UIDevice identifierForVendor] or create a per-install UUID.
You can use your alternative for Apple UDID already. Kind guy gekitz wrote category on UIDevice which will generate some kind of UDID based on device mac-address and bundle identifier.
You can find code on github
Based on the link proposed by @moonlight, i did several tests and it seems to be the best solution. As @DarkDust says the method goes to check en0 which is always available.
There are 2 options:
uniqueDeviceIdentifier (MD5 of MAC+CFBundleIdentifier)
and uniqueGlobalDeviceIdentifier (MD5 of the MAC), these always returns the same values.
Below the tests i've done (with the real device):
#import "UIDevice+IdentifierAddition.h"
NSLog(@"%@",[[UIDevice currentDevice] uniqueDeviceIdentifier]);
NSLog(@"%@",[[UIDevice currentDevice] uniqueGlobalDeviceIdentifier]);
XXXX21f1f19edff198e2a2356bf4XXXX - (WIFI)UDID
XXXX7dc3c577446a2bcbd77935bdXXXX - (WIFI)GlobalAppUDID
XXXX21f1f19edff198e2a2356bf4XXXX - (3G)UDID
XXXX7dc3c577446a2bcbd77935bdXXXX - (3G)GlobalAppUDID
XXXX21f1f19edff198e2a2356bf4XXXX - (GPRS)UDID
XXXX7dc3c577446a2bcbd77935bdXXXX - (GPRS)GlobalAppUDID
XXXX21f1f19edff198e2a2356bf4XXXX - (AirPlane mode)UDID
XXXX7dc3c577446a2bcbd77935bdXXXX - (AirPlane mode)GlobalAppUDID
XXXX21f1f19edff198e2a2356bf4XXXX - (Wi-Fi)after removing and reinstalling the app XXXX7dc3c577446a2bcbd77935bdXXXX (Wi-Fi) after removing and installing the app
Hope it's useful.
EDIT:
As others pointed out, this solution in iOS 7 is no longer useful since uniqueIdentifier is no longer available and querying for MAC address now returns always 02:00:00:00:00:00
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