Xcode:视图控制器和App Delegate之间的连接

import UIKit

class ViewController: UIViewController {
    var appDelegate: AppDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()

        // 获取App Delegate实例
        appDelegate = UIApplication.shared.delegate as? AppDelegate

        // 将视图控制器作为App Delegate的代理
        appDelegate?.delegate = self
    }
}

extension ViewController: AppDelegateDelegate {
    func didReceiveMessage(_ message: String) {
        // 在这里处理App Delegate发送的消息
    }
}

protocol AppDelegateDelegate: AnyObject {
    func didReceiveMessage(_ message: String)
}

class AppDelegate: UIResponder, UIApplicationDelegate {
    var delegate: AppDelegateDelegate?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // 在这里执行应用程序启动时的操作
        return true
    }

    func sendMessage(_ message: String) {
        // 通过代理将消息发送给视图控制器
        delegate?.didReceiveMessage(message)
    }
}