extension AppDelegate {

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

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
    

extension AppDelegate {

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

在Xcode 6.2中，这也是可行的

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

let aVariable = appDelegate.someVariable

非常简单

应用程序委托实例

let app = UIApplication.shared.delegate as! AppDelegate

可以使用一行语法调用方法

app.callingMethod()

您可以使用这段代码访问一个变量

app.yourVariable = "Assigning a value"

这可以用于OS X

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