1、首先建立一個AppDelegate類並繼承UIResponder、UIApplicationDelegate，其中UIResponder可以通過建立類時在繼承，而UIApplicationDelegate只能手動新增，如下圖所示：

2、手動新增UIApplicationDelegate繼承以及程式碼，其中最關鍵的是@UIApplicationMain，表示函式的入口，如下程式碼所示：

//
//  AppDelegate.swift
//  News
//
//  Created by 孫曉舉 on 2018/7/3.
//  Copyright © 2018年 孫曉舉. All rights reserved.
//

import UIKit
@UIApplicationMain
class AppDelegate: UIResponder,UIApplicationDelegate {
    var window: UIWindow?
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        /// 設定主題顏色
        window = UIWindow(frame: UIScreen.main.bounds)
        
        window?.makeKeyAndVisible()
        print("IOS 文字文件 hahahahhHAHAHHAhhahfjdsfjdslfjs")
        return true
    }
    
    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }
    
    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }
    
    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }
    
    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }
    
    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }
}
 

3、然後啟動並檢視輸出，如下圖所示說明函式進入到了自定義的類中：