我的
swift应用程序中有两个视图.我正在执行如下的segue.
ViewController.swift —————–> GameViewController.swift
加载GameViewController时,一个值数组也从ViewController.swift传递给GameViewController.swift
应该在GameViewController.swift中初始化一个计时器
以下是我的代码片段.
ViewController.swift
func signIn(difficultyLvl:String){
let username = usernameTxt.text
let password = passwordTxt.text
let url = URL(string: "http://192.168.1.106/speed/scoreBoardController.PHP?username="+username!+"&password="+password!+"&action=SIGNIN")
let task = URLSession.shared.dataTask(with: url!) {(data,response,error) in
let isPassed = String(data: data!,encoding:.utf8)?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
var gameViewControllerParams = [Int: [String: String]]()
gameViewControllerParams[0] = ["userId" : isPassed!]
gameViewControllerParams[1] = ["difficultyLvl" : difficultyLvl]
if(isPassed != "null"){
self.performSegue(withIdentifier: "gotoGame",sender: gameViewControllerParams)
}
}
task.resume()
}
GameViewController.swift
class GameViewController: UIViewController {
var gameViewControllerParams = [Int: [String: String]]()
override func viewDidLoad() {
super.viewDidLoad()
let _ = Timer.scheduledTimer(timeInterval: 1.0,target:self,selector: #selector(self.setCalculationLs),userInfo:nil,repeats: true)
}
func setCalculationLs(){
print("Timing")
}
}
解决方法
定时器不适用于后台队列(没有一些涉及创建运行循环或在现有运行循环上手动调度它的手段).但是你绝不应该从主队列以外的任何东西发起任何UI更新.
因此,由于您从URLSession完成闭包(在后台队列上运行)调用performSegue,它实际上也在后台队列中运行viewDidLoad.因此,计划定时器的尝试失败.要解决此问题,您必须手动将performSegue代码分派到主队列：
let task = URLSession.shared.dataTask(with: url!) { data,error in
...
if isPassed != "null" {
DispatchQueue.main.async {
self.performSegue(withIdentifier: "gotoGame",sender: ...)
}
}
}
如果您不确定某些代码是否在主队列上运行,请参阅the documentation.或者您可以使用调度前提条件：
dispatchPrecondition(condition: .onQueue(.main))
这样,如果您不小心从后台队列中调用了代码,它将(在调试版本中)停止应用程序.
与您当前的问题无关,但另外,为了避免计时器和视图控制器之间的强引用周期,您通常希望保留对计时器的引用,以便在视图消失时使其无效(例如,创建计时器) viewDidAppear并在viewDidDisappear中删除它.否则你可以在解雇后最终保留GameViewController,例如：
class GameViewController: UIViewController {
var timer: Timer?
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
timer = Timer.scheduledTimer(timeInterval: 1.0,selector: #selector(setCalculationLs),userInfo: nil,repeats: true)
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
timer?.invalidate()
}
func setCalculationLs() {
print("Tick")
}
}
或者在iOS 10中,您可以使用基于块的变体,对自身的弱引用,以及在deinit中无效：
class GameViewController: UIViewController {
var timer: Timer?
override func viewDidLoad() {
super.viewDidLoad()
timer = Timer.scheduledTimer(withTimeInterval: 1.0,repeats: true) { [weak self] timer in
self?.setCalculationLs()
}
}
deinit {
timer?.invalidate()
}
func setCalculationLs() {
print("Tick")
}
}
