extension AppDelegate {

    // MARK: - App Delegate Ref
    class func delegate() -> 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?

以下是Swift 5的版本:

let delegate = UIApplication.shared.delegate as? AppDelegate

并访问管理对象上下文:

    if let delegate = UIApplication.shared.delegate as? AppDelegate {

        let moc = delegate.managedObjectContext
        
        // your code here
        
    }

或者，用guard:

    guard let delegate = UIApplication.shared.delegate as? AppDelegate  else {
        return
    }

    let moc = delegate.managedObjectContext
        
    // 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

在Xcode 6.2中，这也是可行的

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

let aVariable = appDelegate.someVariable

在我的情况下，我错过了导入UIKit在我的NSManagedObject子类。 导入后，我可以删除这个错误，因为UIApplication是UIKit的一部分

希望它能帮助到其他人!!