swift中利用runtime交换方法的实现示例

 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)  } }

 extension UIApplication {   private static let runOnce: Void = {    NothingToSeeHere.harmlessFunction()   }()  override open var next: UIResponder? {    // Called before applicationDidFinishLaunching    UIApplication.runOnce    return super.next  } } 

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

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 }}

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

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  } }}

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) }}