gistfile1.m

// AppDelegate.m

- (void)applicationDidFinishLaunching {
    ...
    if ([SKPaymentQueue canMakePayments]) {
        [[SKPaymentQueue defaultQueue] addObserver:self];
    }
    ...
}


- (void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions {
    // processing code
    [[NSNotificationCenter defaultCenter] postNotificationName:@"MyPurchaseNotification" object:self];
}

// MyPurchaseClass.m
- (void)viewDidLoad {
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(gotTransactionNotification:) name:@"MyPurchaseNotification" object:nil];
}