Question

每次用户点击我的应用程序图标并打开它时，我想调用名为update的函数。我该怎么办？无论何时应用程序启动，我都可以覆盖哪种方法可以覆盖后台或用户按下主页按钮。

 import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

    @IBOutlet weak var button: UIButton!

    @IBOutlet weak var labeltwo: UILabel!

    var NSDateDefalt = NSUserDefaults.standardUserDefaults()
    var date : NSDate?

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        date = NSUserDefaults.standardUserDefaults().objectForKey("yourKey") as? NSDate
        label.text = "\(date)"
        update()
    }


    @IBAction func buttona(sender: AnyObject) {
        date = NSDate()
        label.text = "\(date)"

        NSUserDefaults.standardUserDefaults().setObject(NSDate(), forKey:"yourKey")
    }



    func update(){
        let now = NSDate()
        let seconds = now.timeIntervalSinceDate(date!)
        labeltwo.text = "\(seconds))"
    }

}

更新：我在我的App Delegate

中实施

 func applicationWillEnterForeground(application: UIApplication) {
        ViewController().update()     
    }

Answer 1

您需要在AppDelegate中实现您的逻辑

class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: NSDictionary?) -> Bool {

        // first launch
        // this method is called only on first launch when app was closed / killed
        return true
    }

    func applicationWillEnterForeground(application: UIApplication) {

        // app will enter in foreground
        // this method is called on first launch when app was closed / killed and every time app is reopened or change status from background to foreground (ex. mobile call)
    }

    func applicationDidBecomeActive(application: UIApplication) {

        // app becomes active
        // this method is called on first launch when app was closed / killed and every time app is reopened or change status from background to foreground (ex. mobile call)
    }
}

<强>更新

正如Paulw11所建议的那样，考虑使用applicationWillEnterForeground而不是applicationDidBecomeActive

Answer 2

在ViewController.swift中viewDidLoad()以相应方式编写其中任何一个：

NotificationCenter.default.addObserver(self, selector: #selector(self.update), name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(self.update), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil)

（编辑：Swift 3更新）

（编辑：删除了这篇文章中不正确的部分内容.iOS会自动向任何添加的观察者触发这些通知，无需在App Delegate中添加代码来触发它们）

Answer 3

在您的AppDelegate.swift中，有didFinishLaunchingWithOptions和applicationWillEnterForeground。

applicationWillEnterForeground与您的viewControllers相比，viewWillAppear与您的应用相似，而didFinishLaunchingWithOptions类似于您应用的viewDidLoad。有关详细信息，请查看UIApplicationDelegate

Answer 4

使用UIApplicationDidBecomeActive通知。

Answer 5

当应用程序处于已终止状态且用户点击应用程序图标时，首先调用的方法是

didFinishLaunchingWithOptions

当应用程序处于后台模式并进入前台时

applicationWillEnterForeground

所以你可以在两个方法中调用Update（）。但是当didFinishLaunchingWithOptions调用的方法不在applicationWillEnterForeground中调用时。因为当app启动时调用这两个方法，当app进入前台模式时，只有WillEnterForeground方法调用。这可以通过bool flag来管理

Answer 6

对于 Swift 5 ，请使用此代码

在func viewDidLoad()
中添加此行
NotificationCenter.default.addObserver(self, selector: #selector(self.updateView), name: UIApplication.didBecomeActiveNotification, object: nil)
添加此功能

@objc func updateView（）{

}

每次用户打开应用程序时如何调用函数

6 个答案: