In Swift, how do I have a UIScrollView subclass that has an internal and external delegate?

Question

I\'m subclassing UIScrollView to add some features such as double tap to zoom and an image property for gallery purposes. But in order to do the image part my s

Answer 1

Swift 4+ version of rintaro's excellent answer:

class MyScrollView: UIScrollView {
    class _DelegateProxy: NSObject, UIScrollViewDelegate {
        weak var _userDelegate: UIScrollViewDelegate?

        override func responds(to aSelector: Selector!) -> Bool {
            return super.responds(to: aSelector) || _userDelegate?.responds(to: aSelector) == true
        }

        override func forwardingTarget(for aSelector: Selector!) -> Any? {
            if _userDelegate?.responds(to: aSelector) == true {
                return _userDelegate
            }

            return super.forwardingTarget(for: aSelector)
        }

        //This function is just a demonstration, it can be replaced/removed.
        func scrollViewDidScroll(_ scrollView: UIScrollView) {
            (scrollView as? MyScrollView)?.didScroll()

            _userDelegate?.scrollViewDidScroll?(scrollView)
        }
    }

    fileprivate let _delegateProxy = _DelegateProxy()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        super.delegate = _delegateProxy
    }

    override init(frame: CGRect) {
        super.init(frame: frame)

        super.delegate = _delegateProxy
    }

    override var delegate: UIScrollViewDelegate? {
        get {
            return _delegateProxy._userDelegate
        }

        set {
            _delegateProxy._userDelegate = newValue
        }
    }

    func didScroll() {
        print("didScroll")
    }
}