Swift Swizzle

gistfile1.txt

//
//  Swizzle.swift
//  RouterTester
//
//  Created by Ivan Bruel on 17/05/2017.
//  Copyright © 2017 Unbabel. All rights reserved.
//

import Foundation
import ObjectiveC
import UIKit

struct Swizzling {

  typealias ViewDidAppearFunction = @convention(c) (UIViewController, Selector, Bool) -> Void
  typealias ViewDidAppearBlock = @convention(block) (UIViewController, Selector, Bool) -> Void

  static private func swizzleViewDidAppear(_ class_: AnyClass, to block: @escaping ViewDidAppearBlock) -> IMP? {

    let selector = #selector(UIViewController.viewDidAppear(_:))
    let method: Method? = class_getInstanceMethod(class_, selector)
    let newImplementation: IMP = imp_implementationWithBlock(unsafeBitCast(block, to: AnyObject.self))

    if let method = method {
      let oldImplementation: IMP = method_getImplementation(method)
      method_setImplementation(method, newImplementation)
      return oldImplementation
    } else {
      class_addMethod(class_, selector, newImplementation, "")
      return nil
    }
  }

  static private func removeViewDidAppearSwizzle(_ class_: AnyClass, originalImplementation: IMP?) {
    let selector = #selector(UIViewController.viewDidAppear(_:))
    guard let method: Method? = class_getInstanceMethod(class_, selector) else { return }
    method_setImplementation(method, originalImplementation)
  }

  static func swizzleViewDidAppear(viewController: UIViewController, to block: @escaping (UIViewController) -> Void) {
    var implementation: IMP?
    let class_ = type(of: viewController)
    let swizzledBlock: ViewDidAppearBlock = { calledViewController, selector, animated in
      if let implementation = implementation {
        let viewDidAppear: ViewDidAppearFunction = unsafeBitCast(implementation, to: ViewDidAppearFunction.self)
        viewDidAppear(calledViewController, selector, animated)
      }
      if viewController == calledViewController {
        block(viewController)
        removeViewDidAppearSwizzle(class_, originalImplementation: implementation)
      }
    }
    implementation = swizzleViewDidAppear(class_, to: swizzledBlock)
  }
}

Hey, nice code, why do you remove it again?

Unfortunately, this does not work as intended:
Documentation for imp_implementationWithBlock states, that "The selector is not available as a parameter to this block", thus it is null inside the ViewDidAppearBlock.
A working way would be to remove Selector from ViewDidAppearBlock and call let selector = #selector(UIViewController.viewDidAppear(_:)) inside the block. (See my fork)