Swizzling NSObject classes in Swift

Transcript

1. Swizzing NSObject classes
   Kaz Yoshikawa
   FEB 2021
   

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2. Swizzling
   • To be able to replace or to override existing NSObject methods
   
   •
   UIViewController
   viewDidAppear
   UIViewController
   myViewDidAppear
   viewDidAppear
   Before
   After
   viewDidAppear viewDidAppear
   

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3. What’s for?
   • Analytics for user tracking
   
   • eg. Logging extra information of all viewDidAppear methods
   
   • Application wide behavior changes
   
   • Tap on UIButton to speech before sendAction() get invoked
   

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4. Example
   func swizzleMethod(_ `class`: AnyClass, _ original: Selector, _ swizzled: Selector) {
   
   
   
   
   if let original = class_getInstanceMethod(`class`, original),
   
   
   let swizzled = class_getInstanceMethod(`class`, swizzled) {
   
   
   method_exchangeImplementations(original, swizzled)
   
   
   }
   
   
   else { print("failed to swizzle: \(`class`.self), '\(original)', '\(swizzled)'") }
   
   
   }
   
   
   swizzleMethod(
   
   
   UIViewController.self,
   
   
   #selector(UIViewController.viewDidAppear(_:)),
   
   
   #selector(UIViewController.viewDidAppear_x(_:))
   
   
   )
   
   
   public extension UIViewController {
   
   
   @objc private func viewWillAppear_x(_ animated: Bool) {
   
   
   print(Self.self, #function)
   
   
   self.viewWillAppear_x(animated)
   
   
   }
   
   
   }
   
   
   

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5. Consideration
   • Do not abuse
   
   • Apple may terminate or discontinue this mechanism in the future
   

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6. Code
   • https://gist.github.com/codelynx/3685e0530607746a0811dfd3d1fe
   ff
   9e
   

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7. Thank you
   

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