swift4 交换方法

//
//  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<UITouch>, 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
    }