A UIButton subclass that renders a sort button.

SortButton.swift

fileprivate extension UIControlState {
    static let unspecified = UIControlState(rawValue: 1 << 16)
    static let ascending = UIControlState(rawValue: 1 << 17)
    static let descending = UIControlState(rawValue: 1 << 18)
}

class SortButton: UIButton {
    private var customState: UIControlState = .unspecified {
        didSet {
            setNeedsLayout()
        }
    }
    
    override var state: UIControlState {
        return customState
    }
    convenience init(){
        self.init(frame: .zero)
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.setup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.setup()
    }
    
    private func setup(){
        self.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
        self.setImage(UIImage(named: "column-sort-unspecified"), for: .unspecified)
        self.setImage(UIImage(named: "column-sort-ascending"), for: .ascending)
        self.setImage(UIImage(named: "column-sort-descending"), for: .descending)
        //Safety feature. Find out how to make this comply, 16 bit vs 8 bit issue
        //assert(UIControlState.unspecified & UIControlState.application, "The custom state is not within UIControlStateApplication")
        //assert(UIControlState.ascending & UIControlState.application, "The custom state is not within UIControlStateApplication")
        //assert(UIControlState.descending & UIControlState.application, "The custom state is not within UIControlStateApplication")
        setUnspecified()
    }
    override func setTitle(_ title: String?, for state: UIControlState) {
        print("Setting the title on this SortButton I've created is not supported yet, mainly because I haven't figured out a nice way to cater for the layout")
    }
    
    @objc func buttonTapped(){
        self.toggle()
    }
    func setUnspecified(){
        self.customState = UIControlState.unspecified
    }
    
    func setAscending(){
        self.customState = .ascending
    }
    func setDescending(){
        self.customState = .descending
    }
    
    func toggle(){
        //Escape early if the state is unspecified and toggle to ascending.
        guard self.customState != .unspecified else {
            self.setAscending()
            return
        }
        if self.customState == .ascending {
            self.setDescending()
        }
        else {
            self.setAscending()
        }
    }
}