完成/线程订单协助

Posted 2023-02-23

【中文标题】完成/线程订单协助

【英文标题】：Completion/Threading order assistance

【发布时间】：2020-04-08 20:26:51

【问题描述】：

我搞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：

Time Lapsed 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，这很好。

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A类中：

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A类中：

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 B 类的 viewDidLoad 中：

 let start = Date()

    Variables.loadDataAndSignIn 

        self.removeLoadingScreen()

        let end = Date()

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

需要帮助我的线程/完成块按顺序恢复。

【参考方案1】：

在getDataFromFirestore 的完成处理程序中调用completion，它在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 nil，您可能还想调用完成，例如：

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

            DispatchQueue.main.async 
                completion()