SwiftLoadHook 中文介绍

Purpose

This lib uses a hack way to achieve similar functions as Load() or initialize().

Reason

Upon migrating a project to Swift 3.1, Xcode raises a warning:

Method ‘initialize()’ defines Objective-C class method ‘initialize’, which is not guaranteed to be invoked by Swift and will be disallowed in future versions.

Requirements

• iOS 8.0+
• swift 3.0+

Usage

First, drop files under Sources folder to your project.

Then, your target class should conforms to SelfAware protocol, and implements the functions in SelfAware protocol.

Finally, write the code you want in awake function just like that in Load() or Initialize().

Example

This example is used to help you understand how to use, you can find the code in the files under Example folder. In this example, I want to swizzle the IMP of function viewWillAppear() in UIViewController.

First, UIViewController should conform to SelfAware protocol and implement functions of the protocol.

extension UIViewController: SelfAware {

  static func awake() {
    UIViewController.classInit()
  }

  static func classInit() {
    swizzleMethod
  }
}

Then, I should implement swizzleMethod function. while swizzling methods, we should use dispatch_once in Load() or Initialize() function. However, since swift 3.x, we cannot find dispatch_once in API. How can we handle this? We can use static let instance to handle with it.

@objc func swizzled_viewWillAppear(_ animated: Bool) {
    swizzled_viewWillAppear(animated)
    print("swizzled_viewWillAppear")
  }

  private static let swizzleMethod: Void = {
    let originalSelector = #selector(viewWillAppear(_:))
    let swizzledSelector = #selector(swizzled_viewWillAppear(_:))
    swizzlingForClass(UIViewController.self, originalSelector: originalSelector, swizzledSelector: swizzledSelector)
  }()

  private static func swizzlingForClass(_ forClass: AnyClass, originalSelector: Selector, swizzledSelector: Selector) {

    let originalMethod = class_getInstanceMethod(forClass, originalSelector)
    let swizzledMethod = class_getInstanceMethod(forClass, swizzledSelector)

    guard (originalMethod != nil && swizzledMethod != nil) else {
      return
    }

    if class_addMethod(forClass, originalSelector, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!)) {
      class_replaceMethod(forClass, swizzledSelector, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))
    } else {
      method_exchangeImplementations(originalMethod!, swizzledMethod!)
    }
  }

Thanks

@JORDAN SMITH

Reference

Handling the Deprecation of initialize()

License

SwiftLoadHook is released under the MIT license. See LICENSE for details.