Completion/Threading 订单协助

Question

我弄乱了我的完成处理程序的顺序，可能还有我的线程。我使用打印语句和计时器来检查我的工作，这是我发现的：

延时为 0.00076 秒，这显然不是预期的行为。
第 4 步立即显示，这又不是预期的行为。
显示第 1 步
第 2 步的显示时间为 2.92 秒，没问题。

唯一需要解决的问题是将第 4 步放在最后，因为这意味着第 1 步和第 2 步已完成。

这个函数在classA:

static func loadDataAndSignIn(completion: @escaping () -> () ) {

    let start = Date()

        Auth.auth().signInAnonymously { (result, error) in
            if result != nil {

                print("Step 1 -> Signed In. UserId is: \(result?.user.uid)")

                Variables.getDataFromFirestore {

                    let end = Date()

                    print("Step 2 - > Data Fetched")
                    print("Data Fetched in \(end.timeIntervalSince(start)) seconds")
                }
            } else {
                print(error?.localizedDescription ?? print("Sign in Error"))
            }
        }

    DispatchQueue.main.async {
         completion()
        print("Step 4 -> Signed In and Data Loaded")
    }
 }

这个函数也在classA:

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

        let db = Firestore.firestore()

        db.collection("Offences").getDocuments { (snapshot, error) in
            if let error = error {
                print("Error getting documents: \(error.localizedDescription)")
            } else {
                Variables.offencesArray.removeAll()

                for offence in snapshot!.documents {

                    let offenceName = offence.get("name") as! String
                    let offencePoints = offence.get("points") as! Int
                    let offenceCost = offence.get("cost") as! Int
                    let offenceSection = offence.get("section") as! String
                    let offenceCategory = offence.get("category") as! String

                    let offenceObject = Offence(section: offenceSection, name: offenceName, cost: offenceCost, points: offencePoints, category: offenceCategory)

                    Variables.offencesArray.append(offenceObject)
                }
            }

            DispatchQueue.main.async {
                completion?()
            } 
        }   
}

这是在 class B:

的 viewDidLoad 中

 let start = Date()

    Variables.loadDataAndSignIn {

        self.removeLoadingScreen()

        let end = Date()

        print("Time lapsed: \(end.timeIntervalSince(start))")
    }

需要帮助才能让我的 threading/completion 块恢复原状。

Answer 1

将对 completion 的调用放入 getDataFromFirestore 的完成处理程序中，它位于 signInAnonymously 的完成处理程序中：

static func loadDataAndSignIn(completion: @escaping () -> () ) {
    Auth.auth().signInAnonymously { (result, error) in
        if result != nil {
            print("Step 1 -> Signed In. UserId is: \(result?.user.uid)")

            Variables.getDataFromFirestore {
                let end = Date()

                print("Step 2 - > Data Fetched")
                print("Data Fetched in \(end.timeIntervalSince(start)) seconds")

                DispatchQueue.main.async {
                    completion()
                    print("Step 4 -> Signed In and Data Loaded")
                }
            }
        } else {
            print(error?.localizedDescription ?? "Sign in Error")
        }
    }
}

注意：如果对 signInAnonymously 的调用中的 result 为零，您可能还想调用完成，例如：

[...]
        } else {
            print(error?.localizedDescription ?? "Sign in Error")

            DispatchQueue.main.async {
                completion()
            }
        }

Completion/Threading 订单协助

Completion/Threading order assistance

multithreading

closures

completionhandler

swift