27-响应式编程
响应式编程
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响应式编程(Reactive Programming，简称RP)
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也是一种编程范式，于1997年提出，可以简化异步编程，提供更优雅的数据绑定
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一般与函数式融合在一起，所以也会叫做:函数响应式编程(Functional Reactive Programming，简称FRP)
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比较著名的、成熟的响应式框架
- ReactiveCocoa
简称RAC，有Objective-C、Swift版本
- ReactiveX
RxSwift
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RxSwift(ReactiveX for Swift)，ReactiveX的Swift版本
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RxSwift的github上已经有详细的安装教程，这里只演示CocoaPods方式的安装
image.png
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模块说明
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RxSwift:Rx标准API的Swift实现，不包括任何iOS相关的内容
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RxCocoa:基于RxSwift，给iOS UI控件扩展了很多Rx特性
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RxSwift 的核心角色
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Observable:负责发送事件(Event)
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Observer:负责订阅Observable，监听Observable发送的事件(Event)
image.png
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种
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next:携带具体数据
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error:携带错误信息，表明Observable终止，不会再发出事件
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completed:表明Observable终止，不会再发出事件
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创建、订阅Observable1
var observable = Observable<Int>.create { observer in
observer.onNext(1)
observer.onCompleted()
return Disposables.create()
}
// 等价于
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()
}
// 等价于
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()
创建、订阅Observable2
let observable = Observable<Int>.timer(.seconds(3),
period: .seconds(1),
scheduler: MainScheduler.instance)
observable.map { "数值是\($0)" }
.bind(to: label.rx.text)
.disposed(by: bag)
创建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 { "数值是\($0)" }.subscribe(binder).dispose()
Observable.just(1).map { "数值是\($0)" }.bind(to: binder).dispose()
扩展 Binder 属性
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)
传统的状态监听
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在开发中经常要对各种状态进行监听，传统的常见监听方案有
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KVO
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Target-Action
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Notification
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Delegate
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Block Callback
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传统方案经常会出现错综复杂的依赖关系、耦合性较高，还需要编写重复的非业务代码
RxSwift 的状态监听1
button.rx.tap.subscribe(onNext: {
print("按钮被点击了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("点击了", person.name)
}).disposed(by: bag)
RxSwift 的状态监听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进入后台", notification) }).disposed(by: bag)
既是Observable，又是Observer
Observable.just(0.8).bind(to: slider.rx.value).dispose()
slider.rx.value.map {
"当前数值是:\($0)"
}.bind(to: textField.rx.text).disposed(by: bag)
textField.rx.text
.subscribe(onNext: { text in
print("text is", text ?? "nil")
}).disposed(by: bag)
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诸如UISlider.rx.value、UTextField.rx.text这类属性值，既是Observable，又是Observer
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它们是RxCocoa.ControlProperty类型
Disposable
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每当Observable被订阅时，都会返回一个Disposable实例，当调用Disposable的dispose，就相当于取消订阅
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在不需要再接收事件时，建议取消订阅，释放资源。有3种常见方式取消订阅
// 立即取消订阅(一次性订阅)
observable.subscribe { event in
print(event)
}.dispose()
// 当bag销毁(deinit)时，会自动调用Disposable实例的dispose
observable.subscribe { event in
print(event)
}.disposed(by: bag)
// self销毁时(deinit)时，会自动调用Disposable实例的dispose
let _ = observable.takeUntil(self.rx.deallocated).subscribe { event in
print(event)
}
