Swizzling

swizzling.swift

// AppDelegate
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    UIViewController.doSwizzleStuff()
}

// extension
// MARK: - Swizzling
private var hasSwizzled = false

extension UIViewController {
    final public class func doSwizzleStuff() {
        guard !hasSwizzled else { return }
        
        hasSwizzled = true
        
        // make sure this isn't a subclass
        if self !== UIViewController.self {
            return
        }
        
        let originalSelector = #selector(viewDidLoad)
        let swizzledSelector = #selector(my_viewDidLoad)
        
        let originalMethod = class_getInstanceMethod(self, originalSelector)
        let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)
        
        guard originalMethod != nil, swizzledMethod != nil else {
            return
        }
        
        let didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!))
        
        if didAddMethod {
            class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))
        } else {
            method_exchangeImplementations(originalMethod!, swizzledMethod!)
        }
    }
    
    // MARK: - Method Swizzling
    @objc func my_viewDidLoad() {
        self.my_viewDidLoad()
    }
}