I'm using StoreKit for in-app purchases. I'm finding that the API is quirky in its behavior when the user presses the "Cancel" button.
For example, if I push Cancel on the "Confirm Your In App Purchase" screen, I get a SKPaymentTransactionStateFailed transaction with error.code == SKErrorPaymentCancelled as I'd expect.
But if I push Buy and then press Cancel, I get a Failed transaction with error.code == 0. The error.localizedDescription is "Cannot connect to iTunes Store" which is clearly a lie.
It's tempting to treat all Failed transactions as ignorable cancellations, but I can also clearly see that if the device is offline in airplane mode, I get a Failed transaction with no alert popup; I should really notify the user to explain the problem in that case.
I note that MKStoreKit assumes all failures are cancellations. MKStoreManager's failedTransaction method is never called; MKStoreObserver always calls transactionCanceled for all Failed transactions. The MKStoreManager.h comments recommend no error message for transactionCanceled, which makes sense, but then who will notify the user about Failed non-cancelled transactions?
What's the best practice for handling these failures? Should I swallow errors? Always show an error, even if it's redundant?
We have a pretty substantial user base buying stuff over mobile connections and only show alerts for
code != SKErrorPaymentCancelled && code != SKErrorPaymentNotAllowed
Apparently, it's the best you can do. I've also seen the weird behavior on cancellation that you mention, which is a framework bug as far as I can tell.