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
}

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
}

这和Objective-C中的基本相同

let del = UIApplication.sharedApplication().delegate

在Xcode 6.2中，这也是可行的

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

let aVariable = appDelegate.someVariable

extension AppDelegate {

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