swizzle

swizzle.swift

extension OSLog {
    static let log = OSLog(subsystem: "", category: "Log")
}

extension UIViewController {
    public class func swizzleTracing() {
        
        // make sure this isn't a subclass
        if self !== UIViewController.self {
            return
        }
        
        struct Inner {
            static let shared: () = {
                let originalSelector = #selector(UIViewController.viewDidLoad)
                let swizzledSelector = #selector(UIViewController.traceViewDidLoad)
                
                guard
                    let originalMethod = class_getInstanceMethod(UIViewController.self, originalSelector),
                    let swizzledMethod = class_getInstanceMethod(UIViewController.self, swizzledSelector)
                else { return }
                
                let didAddMethod = class_addMethod(UIViewController.self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))
                
                if didAddMethod {
                    class_replaceMethod(UIViewController.self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
                } else {
                    method_exchangeImplementations(originalMethod, swizzledMethod);
                }
            }()
        }
        let _ = Inner.shared
    }
    
    // MARK: - Method Swizzling
    
    @objc func traceViewDidLoad() {
            let viewName = self.description
            os_log("Hook viewDidLoad BEGIN", log: OSLog.log, viewName)

            self.traceViewDidLoad()
        
            os_log("Hook viewDidLoad END", log: OSLog.log, viewName)
    }
}