最初我的解决方案是在主控制器文件中的ViewDidLoad()中创建NSTimer类的计时器.这导致我的应用程序中的错误.
我想我需要通过在AppDelegate.swift中使用applicationDidEnterBackground()来终止计时器.但我不确定如何做到这一点.我应该在AppDelegate.swift或主控制器中创建计时器类吗？我不知道Swift文件如何共享类.
我在网上搜索了解决方案,但这些帖子都太旧了,解决方案是用Objective-C编写的.
我绝对是初学者.所以我希望有人可以在Swift中解释它.
这是我的主控制器TodoTableViewController.swift中的代码：
import UIKit
import CoreData
class TodoTableViewController: UITableViewController,NSFetchedResultsControllerDelegate {....
...
...
override func viewDidLoad() {
super.viewDidLoad()
var fetchRequest = NSFetchRequest(entityName: "Todo")
let sortDescriptor = NSSortDescriptor(key: "dayleft",ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
if let managedobjectContext = (UIApplication.sharedApplication().delegate as AppDelegate).managedobjectContext {
fetchResultController = NSFetchedResultsController(fetchRequest:fetchRequest,managedobjectContext: managedobjectContext,sectionNameKeyPath: nil,cacheName: nil)
fetchResultController.delegate = self
var e: NSError?
var result = fetchResultController.performFetch(&e)
todos = fetchResultController.fetchedobjects as [Todo]
if result != true {
println(e?.localizedDescription)
} }
var timer = NSTimer.scheduledTimerWithTimeInterval(10,target: self,selector:"update",userInfo:nil,repeats: true)
}
...
}
如果我要在AppDelegate.swift中使计时器无效,我怎样才能将计时器引用到我在TodoTableViewController.swift中创建的计时器？或许我应该把所有与计时器相关的代码放在AppDelegate.swift中？
更新
我试过使用NSNotificationCenter,这是我的代码.
import UIKit
import CoreData
class TodoTableViewController: UITableViewController,NSFetchedResultsControllerDelegate {
...
var timer = NSTimer.scheduledTimerWithTimeInterval(10,selector:"viewDidLoad",repeats: true)
func update(){
.....
}
override func viewDidLoad() {
super.viewDidLoad()
...
let notificationCenter = NSNotificationCenter.defaultCenter()
notificationCenter.addobserver(self,selector: "didEnterBackground",name: "UIApplicationDidEnterBackgroundNotification",object: UIApplication.sharedApplication())
notificationCenter.addobserver(self,selector: "didBecomeActive",name: "UIApplicationWillEnterForegroundNotification",object: UIApplication.sharedApplication())
}
func didEnterBackground() {
timer.invalidate()
}
func didBecomeActive() {
var timer = NSTimer.scheduledTimerWithTimeInterval(10,repeats: true)
}
...
}
由于计时器是在didBecomeActive()中声明的,因此在didEnterBackground()中有一个错误：没有名为“timer”的成员.如果我在上面发布的代码中声明了didBecomeActive()之外的计时器,那么在调用中会出现“额外参数’选择器’的错误”.我已经将函数update()解析为选择器.我不知道这个错误来自哪里.
解决方法
class TodoTableViewController: UITableViewController,NSFetchedResultsControllerDelegate
//better to instantiate timer inside viewDidLoad
var timer: NSTimer!
func update(){ }
override func viewDidLoad() {
super.viewDidLoad()
startTimer()
let notificationCenter = NSNotificationCenter.defaultCenter()
//UIApplicationDidEnterBackgroundNotification & UIApplicationWillEnterForegroundNotification shouldn't be quoted
notificationCenter.addobserver(self,name: UIApplicationDidEnterBackgroundNotification,object: nil)
notificationCenter.addobserver(self,name: UIApplicationWillEnterForegroundNotification,object: nil)
}
func didEnterBackground() {
self.timer.invalidate()
}
func didBecomeActive() {
startTimer()
}
func startTimer() {
self.timer = NSTimer.scheduledTimerWithTimeInterval(10,repeats: true)
}
}
另请注意,NSTimer强烈保持其目标.所以当关闭viewcontroller时 – 定时器应该是无效的.或者会发生内存泄漏,TodoTableViewController永远不会被破坏.