Since iOS app extensions run as part of a host application rather than as part of their containing app (i.e. your app’s extensions run in somebody else’s app), data sharing isn’t automatic. When you create a shared container for use by an app extension and its containing app in iOS 8, you are obliged to write to that container in a coordinated manner to avoid data corruption. When you create a shared container for use by an app extension and its containing app in iOS 8.0 or later, you are obliged to write to that container in a coordinated manner to avoid data corruption.