在Swift中启动之前如何查看收据（应用内购买）

Question

我想在Swift中启动应用程序之前检查收据。最初，我在didFinishLaunchingWithOptions，AppDelegate中编写了代码。但是它在第一个ViewController出现后就完成了检查。 我要更改举动取决于应用程序内购买（订阅）是否有效。

我该如何实施？

AppDelegate

import StoreKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, SKPaymentManagerDelegate {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        SKProductManager.getSubscriptionProduct()

        SKPaymentManager.shared().delegate = self
        SKPaymentQueue.default().add(SKPaymentManager.shared())

        SKPaymentManager.checkReceipt(handler: { valid in
            receiptValidation()
            isSubscriptionValid = valid
            hideBlock(isValid: isSubscriptionValid) //if subscription is valid, hide all "block" objects in App

            self.window?.makeKeyAndVisible()
        })
    return true
}

SKProductManager

import Foundation
import StoreKit

fileprivate var productManagers : Set<SKProductManager> = Set()

class SKProductManager: NSObject, SKProductsRequestDelegate {
    static var subscriptionProduct : SKProduct? = nil

    fileprivate var completion : (([SKProduct]?,NSError?) -> Void)?

    static func getProducts(withProductIdentifiers productIdentifiers : [String],completion:(([SKProduct]?,NSError?) -> Void)?){
        let productManager = SKProductManager()
        productManager.completion = completion
        let request = SKProductsRequest(productIdentifiers: Set(productIdentifiers))
        request.delegate = productManager
        request.start()

        productManagers.insert(productManager)
    }

    static func getSubscriptionProduct(completion:(() -> Void)? = nil) {

        guard SKProductManager.subscriptionProduct == nil else {
            if let completion = completion {
                completion()
            }
            return
        }

        let productIdentifier = "secret" 

        SKProductManager.getProducts(withProductIdentifiers: [productIdentifier], completion: { (_products, error) -> Void in
            if let product = _products?.first {
                SKProductManager.subscriptionProduct = product
            }
            if let completion = completion {
                completion()
            }
        })

    }

    func productsRequest(_ request: SKProductsRequest, didReceive response: SKProductsResponse) {
        var error : NSError? = nil
        if response.products.count == 0 {
            error = NSError(domain: "ProductsRequestErrorDomain", code: 0, userInfo: [NSLocalizedDescriptionKey:"couldn't get product"])
        }
        completion?(response.products, error)
    }

    func request(_ request: SKRequest, didFailWithError error: Error) {
        let error = NSError(domain: "ProductsRequestErrorDomain", code: 0, userInfo: [NSLocalizedDescriptionKey:"couldn't get product "])
        completion?(nil,error)
        productManagers.remove(self)
    }
    func requestDidFinish(_ request: SKRequest) {
        productManagers.remove(self)
    }
}

SKPaymentManager

///...
public static func checkReceipt(handler:@escaping (Bool)->()) {

var date = NSDate()
var check = false

do {
    let reqeust = try getReceiptRequest()
    let session = URLSession.shared
    let task = session.dataTask(with: reqeust, completionHandler: {(data, response, error) -> Void in
        guard let jsonData = data else { return }

        do {
            let json = try JSONSerialization.jsonObject(with: jsonData, options: .init(rawValue: 0)) as AnyObject
            receiptStatus = ReceiptStatusError.statusForErrorCode(json.object(forKey: "status"))
            guard let latest_receipt_info = (json as AnyObject).object(forKey: "latest_receipt_info") else { return }
            guard let receipts = latest_receipt_info as? [[String: AnyObject]] else { return }
            updateStatus(receipts: receipts)
            var latest = receipts.last

            date = NSDate()
            if let result = latest!["expires_date"] as? String {
                let expireDate = result
                check = checkDifference(now: date, expireDate: expireDate)
                let appDelegate:AppDelegate = UIApplication.shared.delegate as! AppDelegate
                appDelegate.isValid = check
            }

        } catch _ {
           handler(false) 
        }
    })
    task.resume()
} catch let error {
    print("SKPaymentManager : Failure to process payment from Apple store: \(error)")
    checkReceiptInLocal()
    handler(false)
}

return check

}

/// check subscription is valid or not
fileprivate static func checkDifference(now: NSDate, expireDate: String) -> Bool{

    // convert string to Date
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss VV"
    let expire = dateFormatter.date(from: expireDate)

    let dateComponentsFormatter = DateComponentsFormatter()
    dateComponentsFormatter.allowedUnits = [.year,.month,.weekOfMonth,.day,.hour,.minute,.second]
    dateComponentsFormatter.maximumUnitCount = 1
    dateComponentsFormatter.unitsStyle = .full

    dateComponentsFormatter.string(from: now as Date, to: Date(timeIntervalSinceNow: 4000000))  // "1 month"
    dateComponentsFormatter.string(from: expire!, to: Date(timeIntervalSinceNow: 4000000))  // "1 month"

    let seconds = expire?.seconds(from: now as Date)  

    if seconds! > 0 {
        return true
    }else{
        return false
    }

}
///...