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

从iOS 12.2和Swift 5.0开始，AppDelegate不能被识别。UIApplicationDelegate。因此，任何涉及AppDelegate的答案都不再正确。下面的答案是正确的，并避免了强制展开，一些开发人员认为这是一种代码气味:

import UIKit

extension UIViewController {
  var appDelegate: UIApplicationDelegate {
    guard let appDelegate = UIApplication.shared.delegate else {
      fatalError("Could not determine appDelegate.")
    }
    return appDelegate
  }
}

这和Objective-C中的基本相同

let del = UIApplication.sharedApplication().delegate

在Swift 3.0中，你可以通过

let appDelegate = UIApplication.shared.delegate as! AppDelegate

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.

}

这可以用于OS X

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