App crashes with in-app purchase error - ios

Question

I use this code to create my in-app purchase:
import UIKit
import StoreKit
class ViewController: UIViewController, SKProductsRequestDelegate, SKPaymentTransactionObserver, SKStoreProductViewControllerDelegate {
var product_id: String?
#IBOutlet weak var buyButton: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
product_id = "product_id"
SKPaymentQueue.default().add(self)
}
#IBAction func unlockAction(sender: AnyObject) {
print("About to fetch the product...")
// Can make payments
if (SKPaymentQueue.canMakePayments())
{
let productID:NSSet = NSSet(object: self.product_id!);
let productsRequest:SKProductsRequest = SKProductsRequest(productIdentifiers: productID as! Set<String>);
productsRequest.delegate = self;
productsRequest.start();
print("Fetching Products");
}else{
print("Can't make purchases");
}
}
func buyProduct(product: SKProduct){
print("Sending the Payment Request to Apple");
let payment = SKPayment(product: product)
SKPaymentQueue.default().add(payment);
}
func productsRequest (_ request: SKProductsRequest, didReceive response: SKProductsResponse) {
let count : Int = response.products.count
if (count>0) {
let validProduct: SKProduct = response.products[0] as SKProduct
if (validProduct.productIdentifier == self.product_id) {
buyProduct(product: validProduct);
} else {
print(validProduct.productIdentifier)
}
} else {
print("nothing")
}
}
But if I click on button(unlockAction) twice or click once, move on different controller, return and click once more my app crashes on this line:
SKPaymentQueue.default().add(payment);
with error (lldb)
How to fix it?

Answer 1

You have to use viewWillDissappear() function for that in your billing controller. Try that one .
override func viewWillDisappear(_ animated: Bool) {
SKPaymentQueue.default().remove(self)
}
I was also getting that problem and that has been resolve my problem.
The error was with SKPaymentQueue.default().add(payment) line in the code. So try this solution and be reliable productive programmer.
Happy Coding