Question

When user tap the purchase a product button, i wanna show loading indicator before

In-App-Purchase window pops up.

But i don’t know which delegate method i stop the indicator.

Answer 1

you could possible show it when you add the payment to SKPaymentque

    SKPayment *newPayment = [SKPayment paymentWithProduct:aPakage.storeProduct];
   [[SKPaymentQueue defaultQueue] addPayment:newPayment];

For removing you could implement a method for

- (void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions {

[transactionsArray addObjectsFromArray:transactions];
for (SKPaymentTransaction *currentTransaction in transactions) {
    switch (currentTransaction.transactionState) {
        case SKPaymentTransactionStatePurchasing: {
            break;
        }
        case SKPaymentTransactionStatePurchased: {
            [self completeTransaction:currentTransaction];
            break;
        }
        case SKPaymentTransactionStateFailed: {
            [self failedTransaction:currentTransaction];
            break;
        }
        default:
            break;
    }

}

}

you can remove your loading screen when this delegate method is called according to state of the purchase.Me personally implemented two separate functions for failed and succeeded transactions.