UIViewController viewDidLoad swizzling example

UIViewControllerSwizzling.swift

extension UIViewController {
    
    static let shared : UIViewController = {
        $0.initialize()
        return $0
    } (UIViewController())
    
    func initialize() {
        let swizzleClosure: () = {
            UIViewController().swizzleViewDidLoad()
        }()
        swizzleClosure
    }
    
    // MARK: - Helpers
    
    func swizzleViewDidLoad() {
        let originalViewDidLoadSelector = #selector(UIViewController.viewDidLoad)
        let swizzledViewDidLoadSelector = #selector(UIViewController.newViewDidLoad)
        
        guard let originalViewDidLoadMethod = class_getInstanceMethod(UIViewController.self, originalViewDidLoadSelector),
            let swizzledViewDidLoadMethod = class_getInstanceMethod(UIViewController.self, swizzledViewDidLoadSelector) else {
            
            return
        }
        
        let didAddViewDidLoadMethod = class_addMethod(UIViewController.self, originalViewDidLoadSelector, method_getImplementation(swizzledViewDidLoadMethod), method_getTypeEncoding(swizzledViewDidLoadMethod))
        
        if didAddViewDidLoadMethod {
            class_replaceMethod(UIViewController.self, swizzledViewDidLoadSelector, method_getImplementation(originalViewDidLoadMethod), method_getTypeEncoding(swizzledViewDidLoadMethod))
        } else {
            method_exchangeImplementations(originalViewDidLoadMethod, swizzledViewDidLoadMethod)
        }
    }
    
    // MARK: - Method Swizzling.
    
    @objc func newViewDidLoad() {
        // FIXME: add necessary things.
        
        self.newViewDidLoad()
    }
}