map的使用

转换闭包应用于可观察序列发出的元素，并返回转换后的元素的新可观察序列。

 let ob = Observable.of(1,2,3,4)
        ob.map { (number) -> Int in
            return number+2
            }
            .subscribe{
                print("\($0)")
            }
            .disposed(by: disposeBag)

map序列创建

public func map<Result>(_ transform: @escaping (Element) throws -> Result)
        -> Observable<Result> {
        return self.asObservable().composeMap(transform)
    }

map调用composeMap

 internal func composeMap<Result>(_ transform: @escaping (Element) throws -> Result) -> Observable<Result> {
        return _map(source: self, transform: transform)
    }

composeMap初始化_map序列

internal func _map<Element, Result>(source: Observable<Element>, transform: @escaping (Element) throws -> Result) -> Observable<Result> {
    return Map(source: source, transform: transform)
}

实际返回Map序列

final private class Map<SourceType, ResultType>: Producer<ResultType> {
    typealias Transform = (SourceType) throws -> ResultType

    private let _source: Observable<SourceType>

    private let _transform: Transform

    init(source: Observable<SourceType>, transform: @escaping Transform) {
        self._source = source
        self._transform = transform

#if TRACE_RESOURCES
        _ = increment(_numberOfMapOperators)
#endif
    }

Map序列中保存源序列_source,以及转换闭包_transform

map序列订阅

订阅时,会调用Map.run

 override func run<Observer: ObserverType>(_ observer: Observer, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where Observer.Element == ResultType {
        let sink = MapSink(transform: self._transform, observer: observer, cancel: cancel)
        let subscription = self._source.subscribe(sink)
        return (sink: sink, subscription: subscription)
    }

1.创建MapSink

final private class MapSink<SourceType, Observer: ObserverType>: Sink<Observer>, ObserverType {
    typealias Transform = (SourceType) throws -> ResultType

    typealias ResultType = Observer.Element 
    typealias Element = SourceType

    private let _transform: Transform

    init(transform: @escaping Transform, observer: Observer, cancel: Cancelable) {
        self._transform = transform
        super.init(observer: observer, cancel: cancel)
    }

    func on(_ event: Event<SourceType>) {
        switch event {
        case .next(let element):
            do {
                let mappedElement = try self._transform(element)
                self.forwardOn(.next(mappedElement))
            }
            catch let e {
                self.forwardOn(.error(e))
                self.dispose()
            }
        case .error(let error):
            self.forwardOn(.error(error))
            self.dispose()
        case .completed:
            self.forwardOn(.completed)
            self.dispose()
        }
    }
}

保存转换闭包transform,观察者observer,销毁者cancel
2. self._source.subscribe(observer)，MapSink作为观察者,订阅源序列

信号发送响应

源序列每一次发送响应时,就会调用MapSink.on

func on(_ event: Event<SourceType>) {
        switch event {
        case .next(let element):
            do {
                let mappedElement = try self._transform(element)
                self.forwardOn(.next(mappedElement))
            }
            catch let e {
                self.forwardOn(.error(e))
                self.dispose()
            }
        case .error(let error):
            self.forwardOn(.error(error))
            self.dispose()
        case .completed:
            self.forwardOn(.completed)
            self.dispose()
        }
    }

self._transform(element),MapSink.on调用_transform转换闭包进行转换,转换后调用Sink.forwardOn(observer)

 final func forwardOn(_ event: Event<Observer.Element>) {
        #if DEBUG
            self._synchronizationTracker.register(synchronizationErrorMessage: .default)
            defer { self._synchronizationTracker.unregister() }
        #endif
        if isFlagSet(self._disposed, 1) {
            return
        }
        self._observer.on(event)
    }

self._observer.on(event)将回调到外界的订阅闭包中.

总结

map.png