试试简单的方法:

斯威夫特4

// Call the method
(UIApplication.shared.delegate as? AppDelegate)?.whateverWillOccur()

在你的AppDelegate中:

// MARK: - Whatever
func whateverWillOccur() {

    // Your code here.

}

下面是一个UIApplicationDelegate的扩展，它避免了硬编码AppDelegate类名:

extension UIApplicationDelegate {

    static var shared: Self {    
        return UIApplication.shared.delegate! as! Self
    }
}

// use like this:
let appDelegate = MyAppDelegate.shared // will be of type MyAppDelegate

我在Swift 2.3中使用这个功能。

1. 在AppDelegate类中

static let sharedInstance: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

2. 调用AppDelegate

let appDelegate = AppDelegate.sharedInstance

在Xcode 6.2中，这也是可行的

let appDelegate = UIApplication.sharedApplication().delegate! as AppDelegate

let aVariable = appDelegate.someVariable

这可以用于OS X

let appDelegate = NSApplication.sharedApplication().delegate as AppDelegate
var managedObjectContext = appDelegate.managedObjectContext?

在Swift 3.0中，你可以通过

let appDelegate = UIApplication.shared.delegate as! AppDelegate