Swizzling in Swift

Swizzling.swift

import UIKit

extension UIViewController {
  @objc func altViewDidAppear(_ animated: Bool) {
    print("View did appear - \(type(of: self))")
    altViewDidAppear(animated)
  }

  static func swizzle() {
    let originalSelector = #selector(UIViewController.viewDidAppear(_:))
    let altSelector = #selector(UIViewController.altViewDidAppear(_:))
    let originalMethod = class_getInstanceMethod(self, originalSelector)!
    let altMethod = class_getInstanceMethod(self, altSelector)!
    method_exchangeImplementations(originalMethod, altMethod)
  }
}