如何访问“func applicationWillResignActive”中UIViewController的变量？斯威夫特，iOS Xcode

我的 UIViewController 类设置如下：

class ViewController: UIViewController {

    var currentTask: NSURLSessionTask?

    ...

}

如果用户按下主页按钮，我想做

self.currentTask.cancel()

但是我如何从 AppDelegate.swift 访问这个变量？

func applicationWillResignActive(application: UIApplication) {

}

在 UIViewController 类中的 viewDidLoad() 中，添加

    // Add UIApplicationWillResignActiveNotification observer
    NSNotificationCenter.defaultCenter().addObserver(
        self,
        selector: "resigningActive",
        name: UIApplicationWillResignActiveNotification,
        object: nil
    )
    NSNotificationCenter.defaultCenter().addObserver(
        self,
        selector: "becomeActive",
        name: UIApplicationDidBecomeActiveNotification,
        object: nil
    )

对于 Swift 4、iOS 11，请使用以下命令：

 NotificationCenter.default.addObserver(
    self, 
    selector: #selector(ViewController.resigningActive), 
    name: NSNotification.Name.UIApplicationWillResignActive, 
    object: nil)

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

最后将这两个函数添加到您的视图控制器中：

@objc fileprivate func resigningActive() {
    print("== resigningActive ==")
}

@objc fileprivate func becomeActive() {
    print("== becomeActive ==")
}