嵌套 Cloudkit 查询未按正确顺序打印

Question

我的代码打印顺序不正确。我认为这是我使用 dispatch to main 的方式的问题。我想传入一个老板ID。找到具有该 ID 的用户，然后获取他们的 SubscribedBosses 数组。对于该数组中的每个 ID，查询该用户和 return 该用户的 screenName。将这些 screenName 附加到 userArray。之后完成 GetBossSubs 函数和 return userArray（屏幕名称数组）。

现在 .onAppear 的结果是运行在 .onAppear 中的函数实际完成之前。 User Appended 在 Found TestUserName

之前打印

static func getBossSubs(bossID: String, completion: @escaping (Result<UserNames, Error>) ->
    ()) {
    let pred = NSPredicate(format: "uniqueID = %@", bossID)
    let sort = NSSortDescriptor(key: "creationDate", ascending: false)
    let query = CKQuery(recordType: RecordType.Users, predicate: pred)
    query.sortDescriptors = [sort]
    
    let operation = CKQueryOperation(query: query)
    operation.desiredKeys = ["subscribedBosses"]
    operation.resultsLimit = 50
    
    operation.recordFetchedBlock = { record in
        DispatchQueue.main.async {
            guard let subs = record["subscribedBosses"] as? [String] else {
                print("Error at screenName")
                
                completion(.failure(CloudKitHelperError.castFailure))
                return
            }
            let userArray = UserNames() //Error that it should be a LET is here. 
            for boss in subs{
                CloudKitHelper.getBossScreenName(bossID: boss) { (result) in
                    
                    switch result{
                        
                    case .success(let name):
                        userArray.names.append(name) //works fine
                        print("Found \(userArray.names)") //Prints a name
                    case .failure(let er):
                        completion(.failure(er))
                    }
                    
                }
                
                
            }
            print("does this run?") // Only runs if No Name
            completion(.success(userArray)) // contains no name or doesn't run?
        }
    }
    operation.queryCompletionBlock = { (_, err) in
        DispatchQueue.main.async {
            if let err = err {
                completion(.failure(err))
                return
            }
        }
        
    }
    CKContainer.default().publicCloudDatabase.add(operation)
}

我这样调用代码：

.onAppear {
            // MARK: - fetch from CloudKit
            self.userList.names = []
            let myUserID = UserDefaults.standard.string(forKey: self.signInWithAppleManager.userIdentifierKey)!
            // get my subs projects
            CloudKitHelper.getBossSubs(bossID: myUserID) { (results) in
                switch results{
                    
                case .success(let user):
                    print("Users appended")
                    self.userList.names = user.names
                case .failure(let er):
                    print(er.localizedDescription)
                }
            }
        }

Answer 1

这是因为您运行一个异步函数在 另一个 异步函数中。

// this just *starts* a series of asynchronous functions, `result` is not yet available
for boss in subs {
    CloudKitHelper.getBossScreenName(bossID: boss) { result in
        switch result {
        case .success(let name):
            userArray.names.append(name) // works fine
            print("Found \(userArray.names)") // Prints a name
        case .failure(let er):
            completion(.failure(er))
        }
    }
}

// this will run before any `CloudKitHelper.getBossScreenName` finishes
completion(.success(userArray))

一个可能的解决方案可能是检查所有 CloudKitHelper.getBossScreenName 函数是否完成（例如，通过检查 userArray 的大小）然后才 return 完成：

for boss in subs {
    CloudKitHelper.getBossScreenName(bossID: boss) { result in
        switch result {
        case .success(let name):
            userArray.names.append(name)
            if userArray.names.count == subs.count {
                completion(.success(userArray)) // complete only when all functions finish
            }
        case .failure(let er):
            completion(.failure(er))
        }
    }
}

// do not call completion here, wait for all functions to finish
// completion(.success(userArray))

嵌套 Cloudkit 查询未按正确顺序打印

Nested Cloudkit queries not printing in the right order

completionhandler

swift

cloudkit

swiftui