Tells the delegate that the protected files are about to become unavailable.
- iOS 4.0+
- tvOS 9.0+
Your singleton app object.
On a device that uses content protection, protected files are stored in an encrypted form and made available only at certain times, usually when the device is unlocked. This notification lets your app know that the device is about to be locked and that any protected files it is currently accessing might become unavailable shortly.
If your app is currently accessing a protected file, you can use this method to release any references to that file. Although it is not an error to access the file while the device is locked, any attempts to do so will fail. Therefore, if your app depends on the file, you might want to take steps to avoid using that file while the device is locked.