iOS: previously purchased in-app product is restored while purchasing, but transactions are not updated

Question

I have a Xamarin app for iOS with in-app purchases. During testing I've purchased one consumable product but did not finished the transction (crashed on error). Now if I reinstall the app it allows to purchase this product but of course restores it instead and show message "the product was restored for free".

This behaviour is expected, but UpdatedTransactions of queue listener was not fired. I could check the queue directly via StoreKit.SKPaymentQueue.DefaultQueue.Transactions, but I need to know when user interaction finishes (user presses OK in that message dialog). But no listener methods are fired. As I understand from Apple docs there must be transactions' update after this. Maybe it is fired BEFORE I try to purchase. But then, should I check the queue manually before the purchase?

Answer 1

I'm not using Xamarin, but StoreKit is underlaying iOS feature, therefore it cannot work otherwise in Xamarin. The event must be fired earlier. As soon as you add transaction observer ([[SKPaymentQueue defaultQueue] addTransactionObserver:self]), you will receive update callback with all pending transactions. If this is done when app is launched (and it should be), by the time you reach purchase screen you will have transactions updated. For me, this is the trickiest part of IAP development as you have to handle them on application start as well as in all of the screens where you have them and callbacks can happen anytime.

Please also note, that this pending transaction might appear multiple times on the transaction list (I was mainly using non-consumables, so new transaction is added every time you relaunch the app without closing all the pending transactions). For that purpose I had component that is being added as transaction observer as soon as app starts, listens for updated transactions and stores them in instance variable for later use. Before starting a new purchase, I would check if there's a pending transaction with same product id and act accordingly.

Hope this helps.