swift - first自动完成后启动另一个后台进程

Question

我有这个方法

func reminderInitialSetup() {
         DispatchQueue.global(qos: .background).async {

        let center = UNUserNotificationCenter.current()
        center.removeAllPendingNotificationRequests() 

        for i in (0..<self.arrayMyGoals.count) {

            let tempDict1 = self.arrayMyGoals[i] as! NSMutableDictionary;

            var goal_days : String!

            guard let days = tempDict1.value(forKey: "goal_dates") as? String else{
                return
            }
            goal_days = days

            let goal_time = tempDict1.value(forKey: "goal_time") as! String;

            let goal_name = tempDict1.value(forKey: "goal_name") as! String;

            let goalId : Int!

            goalId = tempDict1.object(forKey: "goal_id") as? Int                
            if goal_days.count > 0 {

                var datesArray = [Any]()

                datesArray = goal_days.components(separatedBy: ",")

                for  j in (0..<datesArray.count){

                    self.setReminder(date: datesArray[j] as! String, time: goal_time, title: goal_name, goalId: String(goalId))

                }
            }


        }
        DispatchQueue.main.async {

        }
    }

}

当我在后台单击按钮时从 web 服务获得响应时调用此方法。当我再次按下按钮时，碰巧该方法正在后台执行，并且 arrayMyGoals 中的对象数量发生变化，从而导致崩溃。 我想在上一个完成后自动启动另一个后台进程

我怎样才能做到这一点

Answer 1

您可以为此使用操作队列。示例:

let operationQueue: OperationQueue = {
    let operationQueue = OperationQueue()
    operationQueue.qualityOfService = .background
    operationQueue.maxConcurrentOperationCount = 1
    return operationQueue
}()

func runTask(id: String) {
    // optional: cancel all previous operations if about to start a new one
    // operationQueue.cancelAllOperations()
    operationQueue.addOperation {
        var wait = 0
        for _ in 0 ..< 10000 {
            wait += 1
        }
        DispatchQueue.main.async {
            print("task \(id) finished")
        }
    }
}

runTask(id: "t1")
runTask(id: "t2")
runTask(id: "t3")

输出:

task t1 finished
task t2 finished
task t3 finished