CODEWITHSUNDEEP
iosobjective-cios5core-dataios6
user2081064
user2081064

Reputation:

CoreData - when do I save?

I understand how to use CoreData, but I'm confused when it's best to save the data. When they press the home button? On every interaction in case the app crashes?

Upvotes: 2

Views: 149

Answers (3)

Marcus Adams
Marcus Adams

Reputation: 53880

The reason why saving data is a separate call is so that you can batch multiple smaller changes that comprise a larger operation and save all at once, rather than saving at each step along the way.

You should save the data after each atomic operation, and never have committed data sitting only in memory for any significant period of time.

Each time the user commits a change to the data, they will expect the data to be there the next time they run the app, so it's your job to make sure it's there.

After your user submits a change to the data, your app is likely going to be waiting for the user do something else anyway, so save the data while the user decides what to do next.

If you wait to save data in the applicationDidEnterBackground, there is no guarantee that it will ever be called.

Obviously, not all data is critical, for example, data that a user has entered on a form, but hasn't submitted, is not critical. However, any submitted data is critical.

Upvotes: 4

Dan Shelly
Dan Shelly

Reputation: 6011

If you save in the background, you can do it very often without harming UX much. Remember though that you probably need to update you UI and that will have its impact (merge after save to main will be done on the main thread).
Keep you saves small (small number of objects) so not to stall the main thread.
it is very dependant on your CoreData stack architecture.
You will want to save on critical moments like entering background, or user important data/demand.

Upvotes: 0

arnoapp
arnoapp

Reputation: 2486

I don't think its a good idea to save on every interaction(Honestly your App shouldn't be able to crash on "every" Interaction ;) ). I only save in my app in

- (void)applicationDidEnterBackground:(UIApplication *)application

In fact you are right regarding crashes. But what if an invalid Data causes the crash? So you will reload in the worst case the data so that it crashes every time.

But to be honest that is just an educated guess - I think it depends on how sensitive your Data/App is

edit: This answer provides a similar opinion Saving Core Data Context before Crashing

But there's is a really good point I missed:

you should save whenever the user performs critical operations

Upvotes: 0

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