你可以已经网上找了一些方法发现

////  ViewController.swift//  TestOnce////  Created by point on 2018/5/22.//  Copyright © 2018年 whiteboard. All rights reserved.//import UIKit//extension UIViewController {    public  class func myOnceMethod() {        DispatchQueue.once(token: "ddddddd") {            let originalSelector = Selector.sysP            let swizzledSelector = Selector.sysP2            changeMethod(originalSelector, swizzledSelector, self)        }    }            static func changeMethod(_ original:Selector,_ swizzled:Selector,_ object: AnyClass) -> () {                let originalMethod = class_getInstanceMethod(object, original)        let swizzledMethod = class_getInstanceMethod(object, swizzled)                let didAddMethod: Bool = class_addMethod(object, original, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!))        if didAddMethod {            class_replaceMethod(object, swizzled, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))        } else {            method_exchangeImplementations(originalMethod!, swizzledMethod!)        }    }                    @objc func DCPresent(_ viewControllerToPresent: UIViewController, animated flag: Bool, completion: (() -> Swift.Void)? = nil) {        print("sssss")                DispatchQueue.main.async {            self.DCPresent(viewControllerToPresent, animated: flag, completion: nil)        }    }}fileprivate extension Selector {    //    static let viewWillAppear = #selector(UIViewController.viewWillAppear(_:))    //    static let yz_viewWillAppear = #selector(UIViewController.yz_viewWillAppear(animated:))            static let sysP = #selector(UIViewController.present(_:animated:completion:))    static let sysP2 = #selector(UIViewController.DCPresent(_:animated:completion:))}class ViewController: UIViewController {                    override func viewDidLoad() {        super.viewDidLoad()            }        override func touchesBegan(_ touches: Set
    
     , with event: UIEvent?) {        self.present(SBViewController(), animated: true, completion: nil)            }}extension DispatchQueue {    private static var onceTracker = [String]()        open class func once(token: String, block:() -> Void) {        objc_sync_enter(self)        defer { objc_sync_exit(self) }                if onceTracker.contains(token) {            return        }        onceTracker.append(token)        block()    }}
    

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {        UIViewController.myOnceMethod()        // Override point for customization after application launch.        return true    }