問題：對textField進(jìn)行訂閱，發(fā)現(xiàn)點(diǎn)擊textField會默認(rèn)先執(zhí)行了兩次迟杂，一次是程序啟動后textField初始化時泌枪，一次是成為第一響應(yīng)時耳贬，如下：

textFiled.rx.text.subscribe(onNext: { (text) in
            print("text==  \(text ?? "")")
        })
        .disposed(by: disposeBag)

--------------輸入12，打印醋旦，為什么會有兩次為空的打雍闼？饲齐？----------------
text== 
text== 
text== 1
text== 12

問題二：直接修改textFiled.text,為什么沒有觸發(fā)訂閱钉凌？？（textView會觸發(fā)）

  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        textFiled.text = "touche--textField值改變"
    }

首先為什么textFiled和textView有區(qū)別捂人？

------------textView.rx.text內(nèi)部------------
public var text: ControlProperty<String?> {
        return value
    }
    
    /// Reactive wrapper for `text` property.
    public var value: ControlProperty<String?> {
        let source: Observable<String?> = Observable.deferred { [weak textView = self.base] in
            let text = textView?.text
            
            let textChanged = textView?.textStorage
//注釋中提到了御雕，使用的是通知notifications矢沿，歡迎其他建議.
                // This project uses text storage notifications because
                // that's the only way to catch autocorrect changes
                // in all cases. Other suggestions are welcome.
                .rx.didProcessEditingRangeChangeInLength
                // This observe on is here because text storage
                // will emit event while process is not completely done,
                // so rebinding a value will cause an exception to be thrown.
                .observeOn(MainScheduler.asyncInstance)
                .map { _ in
                    return textView?.textStorage.string
                }
                ?? Observable.empty()
            
            return textChanged
                .startWith(text)
        }
------------textField.rx.text內(nèi)部------------
 internal func controlPropertyWithDefaultEvents<T>(
//通過event事件處理的，而且就兩個 [.allEditingEvents, .valueChanged],
        editingEvents: UIControl.Event = [.allEditingEvents, .valueChanged],
        getter: @escaping (Base) -> T,
        setter: @escaping (Base, T) -> Void
        ) -> ControlProperty<T> {
        return controlProperty(
            editingEvents: editingEvents,
            getter: getter,
            setter: setter
        )
    }

textView的通知是監(jiān)聽文本的改變發(fā)送通知酸纲，textField則是event事件觸發(fā)的捣鲸，所以不一樣，直接修改值并沒有觸發(fā)event事件闽坡。textField的Event 中的valueChanged其實(shí)是沒有意義的栽惶，因?yàn)?code>textField并沒有valueChanged的event事件（滑塊就有），放在這只是因?yàn)?code>UIControl的枚舉中有這個valueChanged而已疾嗅。

解決textField值改變后能響應(yīng)事件的辦法：改變值后添加代碼textFiled.sendActions(for: .allEditingEvents)外厂，意思就是發(fā)生一個allEditingEvents事件出去。

下面主要介紹下為什么會textField有兩次觸發(fā),源代碼如下：

-----------------進(jìn)入textFiled.rx.text方法-----------------
public var text: ControlProperty<String?> {
        return value
    }
public var value: ControlProperty<String?> {
        return base.rx.controlPropertyWithDefaultEvents(
            getter: { textField in
                textField.text
            },
            setter: { textField, value in
                // This check is important because setting text value always clears control state
                // including marked text selection which is imporant for proper input 
                // when IME input method is used.
                if textField.text != value {
                    textField.text = value
                }
            }
        )
    }

----------------- base.rx.controlPropertyWithDefaultEvents  -----------------
internal func controlPropertyWithDefaultEvents<T>(
        editingEvents: UIControl.Event = [.allEditingEvents, .valueChanged],
        getter: @escaping (Base) -> T,
        setter: @escaping (Base, T) -> Void
        ) -> ControlProperty<T> {
        return controlProperty(
            editingEvents: editingEvents,
            getter: getter,
            setter: setter
        )
    }

----------------- controlProperty 最最核心的代碼代承，所有的答案都在這里-----------------
public func controlProperty<T>(
        editingEvents: UIControl.Event,
        getter: @escaping (Base) -> T,
        setter: @escaping (Base, T) -> Void
    ) -> ControlProperty<T> {
        let source: Observable<T> = Observable.create { [weak weakControl = base] observer in
                guard let control = weakControl else {
                    observer.on(.completed)
                    return Disposables.create()
                }
                //  第一次observer.on
                observer.on(.next(getter(control)))

                let controlTarget = ControlTarget(control: control, controlEvents: editingEvents) { _ in
                    if let control = weakControl {
                      //  第二次observer.on
                        observer.on(.next(getter(control)))
                    }
                }
                
                return Disposables.create(with: controlTarget.dispose)
            }
            .takeUntil(deallocated)

        let bindingObserver = Binder(base, binding: setter)

        return ControlProperty<T>(values: source, valueSink: bindingObserver)
    }

進(jìn)入到上面的核心代碼酣衷，好長，這樣來看就好多了：

public func controlProperty<T>(
        editingEvents: UIControl.Event,
        getter: @escaping (Base) -> T,
        setter: @escaping (Base, T) -> Void
    ) -> ControlProperty<T> {
        let source: Observable<T> = Observable.create {...}
            .takeUntil(deallocated)

        let bindingObserver = Binder(base, binding: setter)

        return ControlProperty<T>(values: source, valueSink: bindingObserver)
    }

通過create創(chuàng)建序列次泽，通過Binder訂閱創(chuàng)建觀察者（和subscribe類似的一個方法）穿仪，所以會執(zhí)行第一次observer.on(代碼里面我標(biāo)記了)，所以會輸出一次意荤，我們叫做是rx的textField初始化啊片。
第二次則是在我們點(diǎn)擊textField時，主要分析代碼：

 let controlTarget = ControlTarget(control: control, controlEvents: editingEvents) { _ in
                    if let control = weakControl {
                        observer.on(.next(getter(control)))
                    }
                }

方法傳入了control玖像，event和一個閉包observer.on(.next(getter(control)))紫谷，我們想要知道的就是閉包在什么時候回被調(diào)用，上代碼：

----------------ControlTarget的實(shí)現(xiàn)----------------
final class ControlTarget: RxTarget {
    typealias Callback = (Control) -> Void

    let selector: Selector = #selector(ControlTarget.eventHandler(_:))

    weak var control: Control?
#if os(iOS) || os(tvOS)
    let controlEvents: UIControl.Event
#endif
    var callback: Callback?
    #if os(iOS) || os(tvOS)
    init(control: Control, controlEvents: UIControl.Event, callback: @escaping Callback) {
        MainScheduler.ensureRunningOnMainThread()

        self.control = control
        self.controlEvents = controlEvents
        self.callback = callback

        super.init()

        control.addTarget(self, action: selector, for: controlEvents)

        let method = self.method(for: selector)
        if method == nil {
            rxFatalError("Can't find method")
        }
    }
#elseif os(macOS)
    init(control: Control, callback: @escaping Callback) {...}
#endif

    @objc func eventHandler(_ sender: Control!) {
        if let callback = self.callback, let control = self.control {
            callback(control)
        }
    }

    override func dispose() {...}
}

通過init初始化后捐寥，看到閉包指向了Callback笤昨，也就是self.callback，所以我們希望這個方法被調(diào)用握恳。
control.addTarget(self, action: selector, for: controlEvents)給textField綁定了一個事件selector瞒窒，通過let selector: Selector = #selector(ControlTarget.eventHandler(_:))，selector指向eventHandler乡洼，eventHandler調(diào)用了callback(control)返回自身崇裁，so 閉包被調(diào)用了，問題完美解決束昵。

總結(jié)：第一次是初始化調(diào)用observer.on引起的拔稳；第二次是點(diǎn)擊了textField引起的event事件響應(yīng)。如有寫的不對的地方锹雏，煩請不吝賜教巴比，本人不勝感激~~~