Question

目标

我希望能够循环通过while循环生成随机数。每次迭代一个随机数，如果它不起作用，则另一个迭代。等等。我想从我的数据库中获得一个必须满足三个条件的随机用户。（它们在循环的底部列出）。

挑战

如何确保我的代码按正确的顺序执行？

生成随机数
从数据库获取用户
我们想要用户吗？

A）是的。退出while循环

B）编号。再次从1.开始。我们想要另一个用户

我的结果


static func getRandomUser(){

        var randomNumberID = 1
        var UID = ""
        var current_user: User? = nil

        let dispatchGroup = DispatchGroup()
        let dispatchQueue = DispatchQueue(label: "taskQueue")
        let dispatchSemaphore = DispatchSemaphore(value: 0)

        dispatchQueue.async {

            repeat {

                dispatchGroup.enter()

                // Randomly select one user
                randomNumberID = Int.random(in: 1...Internet.all_time_user_count)

                // Transform generated number to uid with which we can retreave the user from the database
                // E.g. "1" -> "iosdnaui29pbpqwbdabd"
                Internet.getUIDOfUser(with: String(randomNumberID)) { (uid) in

                    UID = uid

                    // Download user from database
                    Internet.getUser(with: uid) { (user) in
                        current_user = user

                        dispatchSemaphore.signal()
                        dispatchGroup.leave()
                    }
                }

                dispatchSemaphore.wait()

                /// Stay in the loop until we find a user
                /// 1. Whom we don't have yet            `Internet.contains(uid: UID, in: discover_users)`
                /// 2. Who exists in the database        `current_user == nil`
                /// 3. Who wants to be found              `current_user?.discoverable == false`
            } while(current_user == nil || current_user?.discoverable == false || Internet.contains(uid: UID, in: discover_users))

            // I want to execute the following line of code when I know that I found an user whith the conditions of the while loop
            discover_users.append(current_user!)
        }

        // Do I need another dispatchGroup like this which notifies me when the whole while-loop is finished?
        dispatchGroup.notify(queue: dispatchQueue) {

            DispatchQueue.main.async {
                print("Another loop iteration finished")
            }
        }

    }

我当前代码所基于的来源：

Swift Closures in for loop

在while循环中执行快速关闭

0 个答案: