ios - 正确配置闭包以捕获结果

Question

我正在编写一些用于应用内购买的自定义商店方法；有点像 SwiftyStore 的包装器。我遇到的问题是无法在关闭之前获取结果。

关于如何正确设置它们有什么建议吗？ IE:关闭...

我有一个函数，可以检查现有订阅，如果在 firebase 中找到订阅，则返回 true，如果没有，则它会前往苹果商店验证之前购买的订阅:

func checkSubscription() -> Bool {
        var RetVal: Bool = false
        var retStat: String = ""
        var myVal: Bool = false

        self.rootRef.child("users").child(self.userID!).observeSingleEvent(of: .value, with: { (snapshot) in
            // Get user value
            let value = snapshot.value as? NSDictionary
            let mySubType = value?["subtyp"] as? String ?? ""
            // set value
            if mySubType == "" {
                // get receipt
                if self.myStore.getReceipt() == true {
                    (myVal, retStat) = self.myStore.verifyPurchase(product: "com.xxxxx.xxxxx.monthly")
                    if myVal == true && retStat == "Valid" {
                        // we have a valid product update firebase
                        print("Valid")
                    } else if myVal == true && retStat == "Expired" {
                        // we have a valid product that is expired
                        print("Expired")
                    }
                }
            } else {
                // we have a purchase, verify its not expired.
                print("Purchased")
                RetVal = true
            }

        }) { (error) in
            print(error.localizedDescription)
        }
        return RetVal
    }

这里的问题是它在闭包完成之前下降到返回 RetVal，因此该函数可能返回无效值。不确定如何在当前设置中解决此问题，但任何建议或指示将不胜感激。

Answer 1

为了扩展 Tom 的评论，如果您想在嵌套异步函数完成时返回结果，您可以传入一个使用 Swift 提供的 Result 类型的完成处理程序闭包，如下所示:

func checkSubscription(completion: @escaping (Result<Bool, Error>) -> Void) {
    var RetVal: Bool = false
    var retStat: String = ""
    var myVal: Bool = false

    self.rootRef.child("users").child(self.userID!).observeSingleEvent(of: .value, with: { (snapshot) in
        // Get user value
        let value = snapshot.value as? NSDictionary
        let mySubType = value?["subtyp"] as? String ?? ""
        // set value
        if mySubType == "" {
            // get receipt
            if self.myStore.getReceipt() == true {
                (myVal, retStat) = self.myStore.verifyPurchase(product: "com.xxxxx.xxxxx.monthly")
                if myVal == true && retStat == "Valid" {
                    // we have a valid product update firebase
                    print("Valid")
                } else if myVal == true && retStat == "Expired" {
                    // we have a valid product that is expired
                    print("Expired")
                }
            }
        } else {
            // we have a purchase, verify its not expired.
            print("Purchased")
            RetVal = true
        }

        completion(.success(RetVal))

    }) { (error) in
        print(error.localizedDescription)
        completion(.failure(error))
    }
}

使用这种类型的完成处理程序调用函数将如下所示:

checkSubscription { (result) in
    switch result {
    case .success(let boolValue):
        // do something with resulting boolean
        break
    case .failure(let error):
        // do something with resulting error
        break
    }
}