響應(yīng)式編程

響應(yīng)式編程（Reactive Programming舌狗，簡(jiǎn)稱RP）

• 也是一種編程范式类腮，于1997年提出椅文，可以簡(jiǎn)化異步編程缭嫡，提供更優(yōu)雅的數(shù)據(jù)綁定
• 一般與函數(shù)式融合在一起缔御，所以也會(huì)叫做：函數(shù)響應(yīng)式編程（Functional Reactive Programming，簡(jiǎn)稱FRP）

比較著名的妇蛀、成熟的響應(yīng)式框架:

• ReactiveCocoa
  簡(jiǎn)稱RAC耕突，有Objective-C、Swift版本
  官網(wǎng)： http://reactivecocoa.io/
  github：https://github.com/ReactiveCocoa

• ReactiveX
  簡(jiǎn)稱Rx评架，有眾多編程語(yǔ)言的版本眷茁，比如RxJava、RxKotlin纵诞、RxJS上祈、RxCpp、RxPHP挣磨、RxGo雇逞、RxSwift等等
  官網(wǎng)： http://reactivex.io/
  github： https://github.com/ReactiveX

RxSwift

• RxSwift（ReactiveX for Swift），ReactiveX的Swift版本
  源碼：https://github.com/ReactiveX/RxSwift
  中文文檔： https://beeth0ven.github.io/RxSwift-Chinese-Documentation/

• RxSwift的github上已經(jīng)有詳細(xì)的安裝教程茁裙，這里只演示CocoaPods方式的安裝

① Podfile

use_frameworks!

target 'target_name' do
pod 'RxSwift', '~> 5'
pod 'RxCocoa', '~> 5'
end

② 命令行

pod repo update
pod install

③ 導(dǎo)入模塊

import RxSwift
import RxCocoa

• 模塊說(shuō)明:
  RxSwift：Rx標(biāo)準(zhǔn)API的Swift實(shí)現(xiàn)塘砸，不包括任何iOS相關(guān)的內(nèi)容
  RxCocoa：基于RxSwift，給iOS UI控件擴(kuò)展了很多Rx特性

RxSwift的核心角色

• Observable：負(fù)責(zé)發(fā)送事件（Event）
• Observer：負(fù)責(zé)訂閱Observable晤锥，監(jiān)聽Observable發(fā)送的事件（Event）

發(fā)出事件為枚舉實(shí)例:

public enum Event<Element> {
    /// Next element is produced.
    case next(Element)
    
    /// Sequence terminated with an error.
    case error(Swift.Error)
    
    /// Sequence completed successfully.
    case completed
}

Event有3種:

• next：攜帶具體數(shù)據(jù)
• error：攜帶錯(cuò)誤信息掉蔬，表明Observable終止，不會(huì)再發(fā)出事件
• completed：表明Observable終止矾瘾，不會(huì)再發(fā)出事件

創(chuàng)建女轿、訂閱Observable

• 發(fā)送一個(gè)事件

var observable = Observable<Int>.create { observer in
    observer.onNext(1)
    observer.onCompleted()
    return Disposables.create()
}
// 等價(jià)于
observable = Observable.just(1) 
observable = Observable.of(1)  
observable = Observable.from([1])

• 發(fā)送多個(gè)事件

var observable = Observable<Int>.create {
    observer in  observer.onNext(1)
    observer.onNext(2)
    observer.onNext(3)
    observer.onCompleted()
    return Disposables.create()
}
// 等價(jià)于
observable = Observable.of(1, 2, 3)
observable = Observable.from([1, 2, 3])

observable.subscribe { event in
    print(event)
}.dispose()

observable.subscribe(onNext: {
    print("next", $0)
}, onError: {
    print("error", $0)
}, onCompleted: {
    print("completed")
}, onDisposed: {
    print("dispose")
}).dispose()

• 創(chuàng)建定時(shí)器

//參數(shù)1: 延遲時(shí)間,  period:間隔時(shí)間,  scheduler: 執(zhí)行線程
let observable = Observable<Int>.timer(.seconds(3),
                                       period: .seconds(1),
                                       scheduler: MainScheduler.instance)
observable.map { "數(shù)值是\($0)" }
    .bind(to: label.rx.text)
    .disposed(by: bag)

創(chuàng)建Observer

• 1>AnyObserver 創(chuàng)建Observer

let observer = AnyObserver<Int>.init { event in
    switch event {
    case .next(let data):
        print(data)
    case .completed:
        print("completed")
    case .error(let error):
        print("error", error)
    }
}
Observable.just(1).subscribe(observer).dispose()

• 2> Binder 創(chuàng)建Observer

let binder = Binder<String>(label) { label, text in
    label.text = text
}
Observable.just(1).map { "數(shù)值是\($0)" }.subscribe(binder).dispose()
Observable.just(1).map { "數(shù)值是\($0)" }.bind(to: binder).dispose()

擴(kuò)展Binder屬性

extension Reactive where Base: UIView {
    var hidden: Binder<Bool> {
        Binder<Bool>(base) { view, value in
            view.isHidden = value
        }
    }
}

let observable = Observable<Int>.interval(.seconds(1),
                                          scheduler: MainScheduler.instance)
observable.map { $0 % 2 == 0 }.bind(to: button.rx.hidden).disposed(by: bag)

傳統(tǒng)的狀態(tài)監(jiān)聽

在開發(fā)中經(jīng)常要對(duì)各種狀態(tài)進(jìn)行監(jiān)聽，傳統(tǒng)的常見監(jiān)聽方案有

• KVO
• Target-Action
• Notification
• Delegate
• Block Callback

傳統(tǒng)方案經(jīng)常會(huì)出現(xiàn)錯(cuò)綜復(fù)雜的依賴關(guān)系壕翩、耦合性較高蛉迹，還需要編寫重復(fù)的非業(yè)務(wù)代碼

RxSwift的狀態(tài)監(jiān)聽1

button.rx.tap.subscribe(onNext: {
    print("按鈕被點(diǎn)擊了1")
}).disposed(by: bag)

let data = Observable.just([
    Person(name: "Jack", age: 10),
    Person(name: "Rose", age: 20)
])
data.bind(to: tableView.rx.items(cellIdentifier: "cell")) { row, person, cell in
    cell.textLabel?.text = person.name
    cell.detailTextLabel?.text = "\(person.age)"
}.disposed(by: bag)

tableView.rx.modelSelected(Person.self)
    .subscribe(onNext: { person in
        print("點(diǎn)擊了", person.name)
    }).disposed(by: bag)

RxSwift的狀態(tài)監(jiān)聽2

class Dog: NSObject {
    @objc dynamic var name: String?
}
dog.rx.observe(String.self, "name")
    .subscribe(onNext: { name in
        print("name is", name ?? "nil")
    }).disposed(by: bag)
dog.name = "larry"
dog.name = "wangwang"

NotificationCenter.default.rx
    .notification(UIApplication.didEnterBackgroundNotification)
    .subscribe(onNext: { notification in
        print("APP進(jìn)入后臺(tái)", notification)
    }).disposed(by: bag)

既是Observable，又是Observer

Observable.just(0.8).bind(to: slider.rx.value).dispose()

slider.rx.value.map {
    "當(dāng)前數(shù)值是：\($0)"
}.bind(to: textField.rx.text).disposed(by: bag)

textField.rx.text
    .subscribe(onNext: { text in
        print("text is", text ?? "nil")
    }).disposed(by: bag)

• 諸如UISlider.rx.value放妈、UTextField.rx.text這類屬性值北救，既是Observable，又是Observer
• 它們是RxCocoa.ControlProperty類型

Disposable

• 每當(dāng)Observable被訂閱時(shí)芜抒，都會(huì)返回一個(gè)Disposable實(shí)例珍策，當(dāng)調(diào)用Disposable的dispose，就相當(dāng)于取消訂閱
• 在不需要再接收事件時(shí)宅倒，建議取消訂閱攘宙，釋放資源。有3種常見方式取消訂閱

1> 立即取消訂閱（一次性訂閱）

observable.subscribe { event in
    print(event)
}.dispose()

2> 當(dāng)bag銷毀（deinit）時(shí)，會(huì)自動(dòng)調(diào)用Disposable實(shí)例的dispose

let bag = DisposeBag()
observable.subscribe { event in
    print(event)
}.disposed(by: bag)

3> self銷毀時(shí)（deinit）時(shí)蹭劈，會(huì)自動(dòng)調(diào)用Disposable實(shí)例的dispose

let _ = observable.takeUntil(self.rx.deallocated).subscribe { event in
    print(event)
}