swift中利用runtime交换方法的实现示例

前言

Runtime介绍

学习一个东西至少要先知道它是个啥，你一定听说过“运行时是 Objective-C 的一个特色”，这里的“运行时”就是指 runtime 了。

老的方式initialize现在已经不适用了，需要用新的方式代替。

思路: 定义一个启动的协议，在app完成启动的方法里把需要做method swizzle的类跑一边协议的方法

第一种

1、Step One

 protocol SelfAware: class {
  static func awake()
 }

 class NothingToSeeHere {
  static func harmlessFunction() {
   let typeCount = Int(objc_getClassList(nil, 0))
   let types = UnsafeMutablePointer<AnyClass?>.allocate(capacity: typeCount)
   let autoreleasingTypes = AutoreleasingUnsafeMutablePointer<AnyClass?>(types)
    objc_getClassList(autoreleasingTypes, Int32(typeCount))
   for index in 0 ..< typeCount { (types[index] as? SelfAware.Type)?.awake() }
   types.deallocate(capacity: typeCount)
  }
 }

2、step two

 extension UIApplication {
   private static let runOnce: Void = {
    NothingToSeeHere.harmlessFunction()
   }()

  override open var next: UIResponder? {
    // Called before applicationDidFinishLaunching
    UIApplication.runOnce
    return super.next
  }
 } 

3、step three

遵循协议SelfAware,实现awake()

第二种(类似第一种)

1、创建一个swizzle注入的协议

public protocol SwizzlingInjection: class {
 static func inject()
}

2、创建swizzle helper

open class SwizzlingManager {
 //只会调用一次的方法
 private static let doOnce: Any? = {
  UIViewController.inject()
  return nil
 }()

 open static func enableInjection() {
  _ = SwizzlingManager.doOnce
 }
}

3、给UIApplication 创建分类调用那个一次方法

extension UIApplication{
 open override var next: UIResponder?{
  SwizzlingManager.enableInjection()
  return super.next
 }
}

4、在你需要的类中遵循注入协议

extension UIViewController: SwizzlingInjection{
  public static func inject() {
  //确保不是子类
  guard self === UIViewController.self else { return }

  DispatchQueue.once(token: "com.moglo.urmoji.UIViewController") {
   //do swizzle method
  }
 }
}

once只执行一次的方法

public extension DispatchQueue {
 private static var _onceTracker = [String]()
 public class func once(file: String = #file, function: String = #function, line: Int = #line, block:()->Void) {
  let token = file + ":" + function + ":" + String(line)
  once(token: token, block: block)
 }

 /**
  Executes a block of code, associated with a unique token, only once. The code is thread safe and will
  only execute the code once even in the presence of multithreaded calls.
  - parameter token: A unique reverse DNS style name such as com.vectorform.<name> or a GUID
  - parameter block: Block to execute once
  */
 public class func once(token: String, block:()->Void) {
  objc_sync_enter(self)
  defer { objc_sync_exit(self) }
  if _onceTracker.contains(token) {
   return
  }
  _onceTracker.append(token)
  block()
 }

 //delay
 typealias Task = (_ cancel : Bool) -> Void
 @discardableResult
 static func delay(time : TimeInterval, task: @escaping () -> ()) -> Task? {

  func dispatch_later(block : @escaping () -> ()) {
   DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + time , execute: block)
  }

  var closure : (() -> ())? = task
  var result : Task?
  let delayedClosure : Task = {
   cancel in
   if let internalClosure = closure {
    if cancel == false {
     DispatchQueue.main.async(execute: internalClosure)
    }
   }
   closure = nil
   result = nil
  }

  result = delayedClosure
  dispatch_later { () -> () in
   if let delayedClosure = result {
    delayedClosure(false)
   }
  }
  return result
 }

 static func cancel(task : Task?) {
  task?(true)
 }
}

总结

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