Example - Custom UIViewController with StoreKit & SwiftyStoreKit

BaseViewController.InApp.swift

//
//  BaseViewController.InApp.swift
//  CrazyMath
//
//  Created by Tien Le P. on 4/4/19.
//  Copyright © 2019 Fx Studio All rights reserved.
//

import StoreKit
import SwiftyStoreKit
import UIKit
import SVProgressHUD

// MARK: User facing alerts
extension BaseViewController {
    //MARK: Get Infor Products
    func getInforAllProducts(identifiers: Set<String>, completed: @escaping (Bool, Set<SKProduct>?) -> ()) {
        SVProgressHUD.show()
        SwiftyStoreKit.retrieveProductsInfo(identifiers) { result in
            SVProgressHUD.dismiss()
            if let error = result.error {
                completed(false, nil)
                self.showAlert(message: error.localizedDescription)
            } else {
                completed(true, result.retrievedProducts)
            }
        }
    }
    
    func getInfor(productIdentifier: String, completed: @escaping (Bool, SKProduct?) -> ()) {
        SVProgressHUD.show()
        SwiftyStoreKit.retrieveProductsInfo([productIdentifier]) { result in
            SVProgressHUD.dismiss()
            if let product = result.retrievedProducts.first {
                completed(true, product)
            }
            else if let invalidProductId = result.invalidProductIDs.first {
                completed(false, nil)
                self.showAlert(message: "Invalid product identifier: \(invalidProductId)")
            }
            else {
                completed(false, nil)
                self.showAlert(message: result.error!.localizedDescription)
            }
        }
    }
    
    //MARK: Purchase
    func buyProduct(productIdentifier: String, completed: @escaping (Bool) -> ()) {
        SVProgressHUD.show()
        SwiftyStoreKit.purchaseProduct(productIdentifier, quantity: 1, atomically: true) { result in
            SVProgressHUD.dismiss()
            switch result {
            case .success(let purchase):
                print("♦️♦️ Purchase Success: \(purchase.productId)")
                completed(true)
            case .error(let error):
                completed(false)
                switch error.code {
                case .unknown:
                    self.showAlert(message:"Unknown error. Please contact support")
                case .clientInvalid:
                    self.showAlert(message:"Not allowed to make the payment")
                case .paymentCancelled: break
                case .paymentInvalid:
                    self.showAlert(message:"The purchase identifier was invalid")
                case .paymentNotAllowed:
                    self.showAlert(message:"The device is not allowed to make the payment")
                case .storeProductNotAvailable:
                    self.showAlert(message:"The product is not available in the current storefront")
                case .cloudServicePermissionDenied:
                    self.showAlert(message:"Access to cloud service information is not allowed")
                case .cloudServiceNetworkConnectionFailed:
                    self.showAlert(message:"Could not connect to the network")
                case .cloudServiceRevoked:
                    self.showAlert(message:"User has revoked permission to use this cloud service")
                default:
                    self.showAlert(message:(error as NSError).localizedDescription)
                }
            }
        }
    }
    
    //MARK: Restore
    func restorePurchases(completed: @escaping (Bool, [String]?) -> ()) {
        SVProgressHUD.show()
        SwiftyStoreKit.restorePurchases(atomically: true) { results in
            SVProgressHUD.dismiss()
            if results.restoreFailedPurchases.count > 0 {
                completed(false, nil)
                print("♦️♦️ Restore Failed: \(results.restoreFailedPurchases)")
                self.showAlert(message: "Restore Failed")
            }
            else if results.restoredPurchases.count > 0 {
                print("♦️♦️ Restore Success: \(results.restoredPurchases)")
                var productIDs: [String] = []
                for purchase in results.restoredPurchases {
                    productIDs.append(purchase.productId)
                }
                completed(true, productIDs)
            }
            else {
                completed(false, nil)
                print("♦️♦️ Nothing to Restore")
            }
        }

    }
}

HomeViewController.swift

        // get info purchase
        self.getInfor(productIdentifier: "YOUR_PRODUCT_IDENTIFIER") { (done, product) in
            // your code
        }
        
        // get info of array products
        self.getInforAllProducts(identifiers: ["YOUR_PRODUCT_IDENTIFIER_1",
                                               "YOUR_PRODUCT_IDENTIFIER_2",
                                               "YOUR_PRODUCT_IDENTIFIER_3"]) { (done, products) in
            // your code
        }
        
        // buy product
        self.buyProduct(productIdentifier: "YOUR_PRODUCT_IDENTIFIER") { (done) in
            // your code
        }
        
        // restore product
        self.restorePurchases { (done, productIDs) in
            // your code
        }

Podfile

  pod 'SwiftyStoreKit'
  pod 'SVProgressHUD'