For a basic app with nonconsumable in-app purchases, has anyone figured out best practices for using SKPaymentQueue's restoreCompletedTransactions
?
Observations
I know it's recommended to always register a transaction observer to receive pending transactions that make their way back to the app, but this is a different question. It looks like restoreCompletedTransactions
is something the app has to actively decide when to call to poll for all the purchases the customer has already made.
From what I can tell, the method is designed to retrieve purchases that may have been lost. For example a customer might install or move an app to a new device in such a way where the app's local records of previous payments are lost or reset.
Concerns
What's not clear to me is how to automatically detect this condition (i.e. how to decide when to poll for missing purchases) in a reliable way. I don't want to screw this up and risk denying a customer access to functionality they've already paid for.
At the same time, I don't want to call restoreCompletedTransactions
every single time the app launches just to be safe and basically get back transactions I already know about 99.9% of the time. (Except for in-app purchasing, my app doesn't really require any network connectivity.)
Notes
Apple documentation clarifies that customers are not charged again for any nonconsumable purchases they have already made. If they try to re-purchase, a payment transaction is still supposedly sent to the app.
Worst-case, a customer could recover purchases this way but I'd still like to avoid walking them down a path that resembles re-purchasing something they've already paid for.
Best Answer
Update (June 2019)
Apple's documentation on this topic was updated in 2018 and is quite comprehensive. Many of its recommendations are consistent with what we ended up figuring out here. The biggest development since this question was first posted in 2009 is the App Store receipt in iOS 7.
In case the link goes stale at some point in the future, I'll quote some of the documentation here.
Previous Answer (2009-2012)
After writing out the question and thinking about it, I came up with a couple solutions.
Automatic (Not Recommended)
One option is to record in user defaults whether
restoreCompletedTransactions
has been called (and successfully completed) yet in the app. If not, the app calls it once on start-up. Since this flag could be stored in the same place as the nonconsumable payments, if user defaults get wiped later on then the restore method would get called again when the app starts.This way, if an existing costumer is somehow doing a fresh install of the app they still get their purchases restored automatically. If they are a new customer that has never launched the app before, then the restore operation returns nothing.
In either case,
restoreCompletedTransactions
is only called once instead of at every launch.Manual (Recommended)
Another option is to offer the customer a "Restore Purchases" button somewhere, hook it up to
restoreCompletedTransactions
and let them decide if and when it might be needed.(The comments below go into why a manual restore is probably better than attempting to do it automatically.)