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Editorial Team
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Asked: 2026-06-03T05:00:23+00:00

I’ve looked around at answers to questions regarding executing core data saves in the

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I’ve looked around at answers to questions regarding executing core data saves in the background, but none that I’ve found have directly addressed the following scenario:

I’ve set up core data so that when my app launches for the first time, core data is populated from a plist and then saved to the persistent store (all on a background thread). During this time, the app displays a “please wait” popup with an animating activity indicator. This seems to work nicely and generally the app will finish the population even if the user hits the home button during the population, pushing the app to the background. However, it is possible that the app could be completely terminated before this population finishes (I’ve successfully done this by hitting home, double-tapping home, and removing the app from the multi-tasking tray really really fast). In this scenario, the app quits without saving the data to the store. On the next launch of the app, the app recognizes that the store already exists, so it doesn’t populate, thus leaving the user with a completely empty database. So the question(s) is/are:

  • Is there a way to completely remove the store on app termination if the population hasn’t finished? I attempted to do this in -applicationWillTerminate: which didn’t seem to properly recognize if the app was in the middle of populating.

  • Or, is there a better way to recognize when the store requires population? E.g., can I determine if the store is empty upon launch?

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1 Answer

  1. Editorial Team

    I would suggest this general approach to your problem:

    1. at the end of the population phase, write a flag to your core data base or to your app defaults (NSUserDefaults);

    2. (now, when the app is terminated before finishing the population phase, the flag will not be stored);

    3. at startup, check for that flag; if it is there, you know that the population phase completed, otherwise you know something went wrong.

    Of course, there is a slight chance that the app is terminated just after the population phase is done and before the flag is stored; aside from this event to be pretty unlikely, in any case, if that happened, it would only force your app to populate the data once again at the next launch, but will not be cause of any data consistency issue.

    A more specific approach is base on the use of beginBackgroundTaskWithExpirationHandler:

    Your app delegate’s applicationDidEnterBackground: method has approximately 5 seconds to finish any tasks and return. In practice, this method should return as quickly as possible. If the method does not return before time runs out, your app is killed and purged from memory. If you still need more time to perform tasks, call the beginBackgroundTaskWithExpirationHandler: method to request background execution time and then start any long-running tasks in a secondary thread. Regardless of whether you start any background tasks, the applicationDidEnterBackground: method must still exit within 5 seconds.

    This will allow you to get more time to complete the population phase before the app is terminated in any “non-pathological” case (i.e., it will not work if the user kills the app like you did in your test, and will not be safe in case something goes wrong in the app itself and it crashes while the background thread is doing the population).

    Hope this helps.

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