In app purchase SKPaymentTransactionStatePurchased

[SkyWalkerDev]

Hello everyone, I'n an italian developer, so excuse me for my English.
I just added one in-app purchase to my app.
When a user click on the "purchase" button and the transaction ends, the "purchase" button is replaced by another button to access to the new features.
But everytime I come back to that page or I close and open again the app, there is again the "purchase" button.
How can I do to have always the new button if the user has purchased the new contents?
Here is my code:

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

    for (SKPaymentTransaction *transaction in transactions) {

		switch (transaction.transactionState) {

			case SKPaymentTransactionStatePurchasing:

				break;

			case SKPaymentTransactionStatePurchased:

			[[SKPaymentQueue defaultQueue] finishTransaction:transaction];

                           UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

                              [button addTarget:self 

                               action:@selector(myaction)

                               forControlEvents:UIControlEventTouchUpInside];

                    [button setTitle:@"mytitle" forState:UIControlStateNormal];

                    

                    button.frame = CGRectMake(156.0, 248.0, 129.0, 36.0);

                    [self.view addSubview:button];

                    break;

			case SKPaymentTransactionStateRestored:

				[[SKPaymentQueue defaultQueue] finishTransaction:transaction];
                         break;

			case SKPaymentTransactionStateFailed:

				if (transaction.error.code != SKErrorPaymentCancelled) {

					NSLog(@"Errorr");

				}

				[[SKPaymentQueue defaultQueue] finishTransaction:transaction];

				
		}

	}

}