Swift中的限定扩展详析

//定义protocol
protocol someProtocol {
 var clickCount: Int { set get }
 func ClickEvent(action: String,value: NSNumber)
}

extension A: someProtocol{
 var clickCount: int { set get } 
 func ClickEvent(action: String,value: NSNumber){
  //实现代码
 }
}

extension someProtocol where Self: UIViewController{
 var otherProperty: String{
  return "something you want"
 }

 func handleError(error: String) {
  //实现代码
}}

//nameTextField是一个UITextField控件，可以直接通过.rx.text获取到该控件中输入内容的事件序列，然后再进行处理

let nameObservable = nameTextField.rx.text .shareReplay(1).map {
 $0!.characters.count > 0 
}

//registerButton是一个UIButton，通过.rx.tap能获取到该button的点击事件序列
registerButton.rx.tap .bindTo(someObservar) .addDisposableTo(disposeBag)

/// Extend NSObject with `rx` proxy.将所有NSObject子类都遵循ReactiveCompatible协议 
extension NSObject: ReactiveCompatible { }
 //ReactiveCompatible这个协议中扩展了rx属性，类型为struct类型的Reactive
extension ReactiveCompatible {
 /// Reactive extensions.
 public var rx: Reactive {
 get {
  return Reactive(self) //此处返回Reactive实体，将self赋给base属性
 }
 set {
  // this enables using Reactive to "mutate" base object
 }
 }
}

public struct Reactive<Base>{ 
 /// Base object to extend. 
 public let base: Base 
 /// Creates extensions with base object. 
 ///
 /// - parameter base: Base object. 
 public init(_ base: Base) {  
  self.base = base //上面的return Reactive(self)，将self赋给了base
 }
}

//点击事件扩展，可通过button.rx.tap来观察订阅
extension Reactive where Base: UIButton {
 /// Reactive wrapper for `TouchUpInside` control event.
 public var tap: ControlEvent {
  return controlEvent(.touchUpInside)
 } 
}

//扩展方法，可通过绑定Observable来动态修改UIButton的title和image
extension Reactive where Base: UIButton {
 /// Reactive wrapper for `setTitle(_:for:)`
 public func title(for controlState: UIControlState = []) -> UIBindingObserver<Base, String?> {
  return UIBindingObserver<Base, String?>(UIElement: self.base) { (button, title) -> () in
   button.setTitle(title, for: controlState)
  }
 }

 /// Reactive wrapper for `setImage(_:for:)`
 public func image(for controlState: UIControlState = []) -> UIBindingObserver<Base, UIImage?> {
  return UIBindingObserver<Base, UIImage?>(UIElement: self.base) { (button, image) -> () in
   button.setImage(image, for: controlState)
  }
 }

 /// Reactive wrapper for `setBackgroundImage(_:for:)`
 public func backgroundImage(for controlState: UIControlState = []) -> UIBindingObserver<Base, UIImage?> {
  return UIBindingObserver<Base, UIImage?>(UIElement: self.base) { (button, image) -> () in
   button.setBackgroundImage(image, for: controlState)
  }
 }
}

//利用限定扩展来自定义对UIButton的Reactive扩展 可以通过rx来访问
extension Reactive where Base:UIButton{
 var btnValidState:UIBindingObserver<Base,Bool>{
  return UIBindingObserver(UIElement: base, binding: { (button, valid) in
   button.isEnabled = valid
   button.backgroundColor = valid ? mainColor : bgGrayColor2
  })
 }
}
//将用户名和密码的String序列转换成Bool序列
let nameObservable = userNameText.rx.text .shareReplay(1).map {
   $0!.characters.count > 0
 }
let passObservable = passwordText.rx.text .shareReplay(1).map {
   $0!.characters.count > 0
 }
//将以上两个序列合成一个序列，绑定到我们扩展的btnValidState属性上
//可以看到此时可以通过loginBtn.rx.btnValidState获取到，这样保持了RxSwift代码的一致性
 _ = Observable.combineLatest(nameObservable,passObservable){$0 && $1}.bind(to: loginBtn.rx.btnValidState).disposed(by: disposeBag)