在上一篇：RxSwift原理-执行流程中，简单分析了一下RxSwift的核心流程，本篇主要针对上一篇做一下更加深入的探究。
继续上篇的demo：
let disposbag: DisposeBag = DisposeBag()
// 1、创建序列
let ob:Observable = Observable.create { (observer) -> Disposable in
// 3、发送信号
observer.onNext("text")
observer.onCompleted()
return Disposables.create()
}
override func touchesBegan(_ touches: Set, with event: UIEvent?) {
// 2、订阅信号
ob.subscribe(onNext: { (text) in
print(text)
}, onCompleted:{
print("订阅完成")
}).disposed(by: disposbag) // 4、销毁
}
流程个人总结如下图，一次创建可以多次订阅，多次响应。
还是按照经典的三部曲来分析：创建序列，订阅信号，发送信号。
创建序列
Observable.create:
public static func create(_ subscribe: @escaping (AnyObserver) -> Disposable) -> Observable {
return AnonymousObservable(subscribe)
}
final private class AnonymousObservable: Producer {
typealias SubscribeHandler = (AnyObserver) -> Disposable
let _subscribeHandler: SubscribeHandler
init(_ subscribeHandler: @escaping SubscribeHandler) {
self._subscribeHandler = subscribeHandler
}
}
来一张创建Observable所涉及类的继承关系图：
总结如下：
-
create方法创建AnonymousObservable对象，传入订阅执行的闭包 -
AnonymousObservable对象使用_subscribeHandler保存了订阅执行的闭包
订阅信号
ob.subscribe:
// '......'表示省略了一些可略过的代码
public func subscribe(onNext: ((E) -> Void)? = nil, onError: ((Swift.Error) -> Void)? = nil, onCompleted: (() -> Void)? = nil, onDisposed: (() -> Void)? = nil)
-> Disposable {
let disposable: Disposable
......
let observer = AnonymousObserver { event in
......
switch event {
case .next(let value):
onNext?(value)
case .error(let error):
if let onError = onError {
onError(error)
}
else {
Hooks.defaultErrorHandler(callStack, error)
}
disposable.dispose()
case .completed:
onCompleted?()
disposable.dispose()
}
}
return Disposables.create(
self.asObservable().subscribe(observer),
disposable
)
}
}
final class AnonymousObserver : ObserverBase {
typealias Element = ElementType
typealias EventHandler = (Event) -> Void
private let _eventHandler : EventHandler
init(_ eventHandler: @escaping EventHandler) {
self._eventHandler = eventHandler
}
}
可以看到，subscribe中创建了一个匿名观察者AnonymousObserver，匿名观察者AnonymousObserver保存了一个响应事件的闭包_eventHandler，咱们来看看AnonymousObserver类的继承关系图：
在创建匿名观察者时有这样一句代码：self.asObservable().subscribe(observer)。这里的self就是咱们上面创建的AnonymousObservable对象ob，observer为AnonymousObserver对象，于是可以替换成ob.subscribe(observer)。根据AnonymousObservable的继承关系，在Producer类中找到了subscribe()的实现，相当于执行：Producer.subscribe(AnonymousObserver)。
class Producer : Observable {
override func subscribe(_ observer: O) -> Disposable where O.E == Element {
if !CurrentThreadScheduler.isScheduleRequired {
// The returned disposable needs to release all references once it was disposed.
let disposer = SinkDisposer()
let sinkAndSubscription = self.run(observer, cancel: disposer)
disposer.setSinkAndSubscription(sink: sinkAndSubscription.sink, subscription: sinkAndSubscription.subscription)
return disposer
}
else {
return CurrentThreadScheduler.instance.schedule(()) { _ in
let disposer = SinkDisposer()
let sinkAndSubscription = self.run(observer, cancel: disposer)
disposer.setSinkAndSubscription(sink: sinkAndSubscription.sink, subscription: sinkAndSubscription.subscription)
return disposer
}
}
}
}
在上面的代码中，self.run(observer, cancel: disposer)是关键，其他的暂时可忽略。self还是咱们的对象ob，于是接着调用AnonymousObservable的run 方法。
override func run(_ observer: O, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where O.E == Element {
let sink = AnonymousObservableSink(observer: observer, cancel: cancel)
let subscription = sink.run(self)
return (sink: sink, subscription: subscription)
}
在run 方法中创建了一个重要角色：AnonymousObservableSink 管道。
创建 sink对象（AnonymousObservableSink(observer: observer, cancel: cancel)）：
override init(observer: O, cancel: Cancelable) {
super.init(observer: observer, cancel: cancel)
}
AnonymousObservableSink的父类Sink：
init(observer: O, cancel: Cancelable) {
self._observer = observer
self._cancel = cancel
}
于是sink对象保存了刚刚创建的匿名观察者observer和Producer.subscribe(AnonymousObserver)中创建的销毁者disposer。
sink.run(self):
func run(_ parent: Parent) -> Disposable {
return parent._subscribeHandler(AnyObserver(self))
}
AnyObserver(self):
public init(_ observer: O) where O.E == Element {
self.observer = observer.on
}
上述代码表明先将sink转换成AnyObserver类型，AnyObserver将sink的on方法保存起来，于是return parent._subscribeHandler(AnyObserver(self))相当于ob执行_subscribeHandler闭包返回一个Disposable。
发送信号
observer.onNext("text")
extension ObserverType {
public func onNext(_ element: E) {
self.on(.next(element))
}
}
public struct AnyObserver : ObserverType {
public func on(_ event: Event) {
return self.observer(event)
}
}
这里的observer(event)就是我们上面保存的sink的on方法，也就是AnonymousObservableSink的on方法。
final private class AnonymousObservableSink: Sink, ObserverType {
func on(_ event: Event) {
#if DEBUG
self._synchronizationTracker.register(synchronizationErrorMessage: .default)
defer { self._synchronizationTracker.unregister() }
#endif
switch event {
case .next:
if load(self._isStopped) == 1 {
return
}
self.forwardOn(event)
case .error, .completed:
if fetchOr(self._isStopped, 1) == 0 {
self.forwardOn(event)
self.dispose()
}
}
}
}
class Sink : Disposable {
final func forwardOn(_ event: Event) {
#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)即为执行上面sink保存的匿名observer的on事件方法，也就是AnonymousObserver的on方法（AnonymousObserver的on没有实现，执行父类ObserverBase的on）。
class ObserverBase : Disposable, ObserverType {
func on(_ event: Event) {
switch event {
case .next:
if load(self._isStopped) == 0 {
self.onCore(event)
}
case .error, .completed:
if fetchOr(self._isStopped, 1) == 0 {
self.onCore(event)
}
}
}
func onCore(_ event: Event) {
rxAbstractMethod()
}
}
final class AnonymousObserver : ObserverBase {
override func onCore(_ event: Event) {
return self._eventHandler(event)
}
}
self._eventHandler(event)即为执行我们之前订阅信号时保存的响应事件闭包。
sink在RxSwift中类似于一个管理者角色，管理序列、观察者和销毁者，将序列发送至观察者，并管理销毁者适时消耗序列，回收资源。
最后一张图作为总结：