RxSwift之销毁者dispose

作为RxSwift四大才子之一，销毁者dispose扮演者举足轻重(灰常重要)的作用

上代码，序列的创建到销毁

         // 创建序列
        let ob = Observable.create { (observer) -> Disposable in
            observer.onNext("Episode:阿拉丁爱吃鱼")
            return Disposables.create { print("销毁释放了")} 
        }
        // 序列订阅
        let dispose = ob.subscribe(onNext: { (anything) in
            print("订阅到了: \(anything)")
        }, onError: { (error) in
            print("订阅到了: \(error)")
        }, onCompleted: {
            print("完成了")
        }) {
            print("销毁回调")
        }
        // status - 算法 - dispose 随时随地都能销毁
        print("执行完毕")
        dispose.dispose()

订阅到了: Episode:阿拉丁爱吃鱼
执行完毕
销毁释放了
销毁回调

销毁者Disposables的源码

extension Disposables {
    public static func create(with dispose: @escaping () -> Void) -> Cancelable {
        return AnonymousDisposable(disposeAction: dispose)
    }

}

1.Disposables.create { print("销毁释放了")}实质上创建了一个AnonymousDisposable类型的销毁者对象
2.传入了业务层的监听dispose闭包，销毁对象时用来通知

fileprivate final class AnonymousDisposable : DisposeBase, Cancelable {

    fileprivate init(_ disposeAction: @escaping DisposeAction) {
        self._disposeAction = disposeAction
        super.init()
    }
   // 核心代码
    fileprivate func dispose() {
        if fetchOr(self._isDisposed, 1) == 0 {
            if let action = self._disposeAction {
                self._disposeAction = nil
                action()
            }
        }
    }
}

AnonymousDisposable遵循了Cancelable协议

public protocol Cancelable : Disposable {
    var isDisposed: Bool { get }
}

Cancelable又遵循了Disposable协议

public protocol Disposable {
    func dispose()
}

dispose()为销毁方法，该方法调用后就销毁了传入的闭包对象，就是最初create的那个

fetchOr(self._isDisposed, 1)这个函数呢

返回值为 oldValue,就是为了保证只有第一次的值为0，后面再次执行就为1，酱紫保证了{}里的方法只走一次

那么问题来了，这个dispose()方法到底是神马时候调用的呢

public func subscribe(onNext: ((Element) -> Void)? = nil, onError: ((Swift.Error) -> Void)? = nil, onCompleted: (() -> Void)? = nil, onDisposed: (() -> Void)? = nil)
        ...
        -> 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
            )
    }
}

so,原来实是在 .error 或者.completed 的时候，调用了 disposable.dispose()

额，那么onNex呢,不禁看到了Disposables.create

return Disposables.create(
                self.asObservable().subscribe(observer),
                disposable
            )

看看这个create的实现

extension Disposables {
    public static func create(_ disposable1: Disposable, _ disposable2: Disposable) -> Cancelable {
        return BinaryDisposable(disposable1, disposable2)
    }
}

private final class BinaryDisposable : DisposeBase, Cancelable {
    func dispose() {
        if fetchOr(self._isDisposed, 1) == 0 {
            self._disposable1?.dispose()
            self._disposable2?.dispose()
            self._disposable1 = nil
            self._disposable2 = nil
        }
    }
}

元祖里的两个对象分别进行了销毁

接下来，我们来看看Producer和拥有着RxSwift世界的Sink

class Producer : Observable {
    override func subscribe(_ observer: Observer) -> Disposable where Observer.Element == Element {
            let disposer = SinkDisposer()
            let sinkAndSubscription = self.run(observer, cancel: disposer)
            disposer.setSinkAndSubscription(sink: sinkAndSubscription.sink, subscription: sinkAndSubscription.subscription)
            return disposer
        }
    }
}

disposer.setSinkAndSubscription

fileprivate final class SinkDisposer: Cancelable {
    func setSinkAndSubscription(sink: Disposable, subscription: Disposable) {
        self._sink = sink
        self._subscription = subscription

        if (previousState & DisposeState.disposed.rawValue) != 0 {
            sink.dispose()
            subscription.dispose()
            self._sink = nil
            self._subscription = nil
        }
    }

我们来看看AnonymousObservableSink，这个连接着序列和观察者的销毁

final private class AnonymousObservableSink: Sink, ObserverType {
func on(_ event: Event) {
    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()
        }
    }
}

so,当订阅序列遇到.error, .completed的时候self.dispose()，咔咔。。。

sink本身是Disposable对象，被销毁后就断开了序列和订阅者之间的联系。