[UIButton+IsCheckedRx] Adds checked behavior to UIButton #uikit #swift

UIButton+Rx.swift

extension Reactive where Base: UIButton {
    /// Alternated with button taps to provide 
    /// a checkbox behavior by `UIButton`
    var checked: ControlProperty<Bool> {
        let button = self.base
        let source: Observable<Bool> = self.tap
            .map {[weak button] in
                guard let state = button?.isSelected else {
                    return false
                }
                return !state
        }
        let binder: AnyObserver<Bool> = self.isSelected.asObserver()
        return ControlProperty(values: source, valueSink: binder)
    }
}