1、首先创建一个AppDelegate类并继承UIResponder、UIApplicationDelegate，其中UIResponder可以通过创建类时在继承，而UIApplicationDelegate只能手动添加，如下图所示：
2、手动添加UIApplicationDelegate继承以及代码，其中最关键的是@UIApplicationMain，表示函数的入口，如下代码所示：
//
// AppDelegate.swift
// News
//
// Created by 孙晓举 on 2018/7/3.
// Copyright © 2018年 孙晓举. All rights reserved.
//
import UIKit
@UIApplicationMain
class AppDelegate: UIResponder,UIApplicationDelegate {
var window: UIWindow?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
/// 设置主题颜色
window = UIWindow(frame: UIScreen.main.bounds)
window?.makeKeyAndVisible()
print("IOS 文本文档 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、然后启动并查看输出，如下图所示说明函数进入到了自定义的类中：
