響應式編程
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響應式編程(Reactive Programming，簡稱RP)
也是一種編程范式，于1997年提出，可以簡化異步編程，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，所以也會叫做:函數(shù)響應式編程(Functional Reactive Programming，簡稱FRP)
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比較著名的、成熟的響應式框架
- ReactiveCocoa
簡稱RAC，有Objective-C、Swift版本
- ReactiveX
RxSwift
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RxSwift(ReactiveX for Swift)，ReactiveX的Swift版本
RxSwift的github上已經(jīng)有詳細的安裝教程，這里只演示CocoaPods方式的安裝
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模塊說明
RxSwift:Rx標準API的Swift實現(xiàn)，不包括任何iOS相關的內(nèi)容
RxCocoa:基于RxSwift，給iOS UI控件擴展了很多Rx特性
RxSwift 的核心角色
Observable:負責發(fā)送事件(Event)
Observer:負責訂閱Observable，監(jiān)聽Observable發(fā)送的事件(Event)
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
}
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Event有3種
next:攜帶具體數(shù)據(jù)
error:攜帶錯誤信息，表明Observable終止，不會再發(fā)出事件
completed:表明Observable終止，不會再發(fā)出事件
創(chuàng)建、訂閱Observable1
var observable = Observable<Int>.create { observer in
observer.onNext(1)
observer.onCompleted()
return Disposables.create()
}
// 等價于
observable = Observable.just(1)
observable = Observable.of(1)
observable = Observable.from([1])
var observable = Observable<Int>.create { observer in
observer.onNext(1)
observer.onNext(2)
observer.onNext(3)
observer.onCompleted()
return Disposables.create()
}
// 等價于
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、訂閱Observable2
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
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()
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
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在開發(fā)中經(jīng)常要對各種狀態(tài)進行監(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)常會出現(xiàn)錯綜復雜的依賴關系、耦合性較高，還需要編寫重復的非業(yè)務代碼
RxSwift 的狀態(tài)監(jiān)聽1
button.rx.tap.subscribe(onNext: {
print("按鈕被點擊了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進入后臺", 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、UTextField.rx.text這類屬性值，既是Observable，又是Observer
它們是RxCocoa.ControlProperty類型
Disposable
每當Observable被訂閱時，都會返回一個Disposable實例，當調(diào)用Disposable的dispose，就相當于取消訂閱
在不需要再接收事件時，建議取消訂閱，釋放資源。有3種常見方式取消訂閱
// 立即取消訂閱(一次性訂閱)
observable.subscribe { event in
print(event)
}.dispose()
// 當bag銷毀(deinit)時，會自動調(diào)用Disposable實例的dispose
observable.subscribe { event in
print(event)
}.disposed(by: bag)
// self銷毀時(deinit)時，會自動調(diào)用Disposable實例的dispose
let _ = observable.takeUntil(self.rx.deallocated).subscribe { event in
print(event)
}
