FilledTextField+Rx.swift

extension Reactive where Base: FilledTextField {
    var delegate: DelegateProxy<FilledTextField, FiledTextFieldDelegate> {
        return FilledTextFieldDelegateProxy.proxy(for: base)
    }
    
    var textDidChange: ControlProperty<String?> {
        let source = delegate.methodInvoked(#selector(FilledTextFieldDelegate.filledTextField(_:textFieldTextDidChange:)))
            .map { params -> String? in
                let text = try castOrThrow(String.self, params[1])
                return text
            }
        let bindingObserver = Binder(base) { (filledTextField, text: String?) in
            filledTextField.textField.text = text
        }
        return ControlProperty(values: source, valueSink: bindingObserver)
    }
    
    var didBeginFocusing: ControlEvent<Void> {
        let source = delegate.methodInvoked(#selector(FilledTextFieldDelegate.filledTextFieldDidBeginFocusing(_:)))
            .map { _ in }
        return ControlEvent(events: source)
    }
}


func castOrThrow<T>(_ resultType: T.Type, _ object: Any) throws -> T {
    guard let returnValue = object as? T else {
        throw RxCocoaError.castingError(object: object, targetType: resultType)
    }
    return returnValue
}