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

确保你导入了UIKit let appDelegate = UIApplication.sharedApplication().delegate!作为!AppDelegate

这可以用于OS X

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

Swift < 3

在AppDelegate类中为ex创建一个方法

func sharedInstance() -> AppDelegate{
        return UIApplication.sharedApplication().delegate as! AppDelegate
    }

叫它"前任"吧

let appDelegate : AppDelegate = AppDelegate().sharedInstance()

Swift >= 3.0

func sharedInstance() -> AppDelegate{
    return UIApplication.shared.delegate as! AppDelegate
}

在Swift 3.0中，你可以通过

let appDelegate = UIApplication.shared.delegate as! AppDelegate

extension AppDelegate {

    // MARK: - App Delegate Ref
    class func delegate() -> AppDelegate {
        return UIApplication.shared.delegate as! AppDelegate
    }
}