问题描述

我正在继承 UIScrollView 以添加一些功能，例如双击缩放和用于图库目的的图像属性.但是为了做图像部分，我的子类必须是它自己的委托并实现 viewForZoomingInScrollView.

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 subclass has to be its own delegate and implement the viewForZoomingInScrollView.

但是当有人使用我的滚动视图子类时，他们可能也希望获得委托通知以查看 scrollViewDidScroll 或您有什么.

But then when someone uses my scroll view subclass, they might like to get delegate notifications as well to see scrollViewDidScroll or what have you.

在 Swift 中，我如何获得这两者?

In Swift, how do I get both of these?

推荐答案

这里是这个模式的 Swift 版本:

Here is a Swift version of this pattern:

虽然 forwardInvocation: 在 Swift 中被禁用，我们仍然可以使用 forwardingTargetForSelector:

Although forwardInvocation: is disabled in Swift, we can still use forwardingTargetForSelector:

class MyScrollView: UIScrollView {

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

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

        override func forwardingTargetForSelector(aSelector: Selector) -> AnyObject? {
            if _userDelegate?.respondsToSelector(aSelector) == true {
                return _userDelegate
            }
            else {
                return super.forwardingTargetForSelector(aSelector)
            }
        }

        func viewForZoomingInScrollView(scrollView: MyScrollView) -> UIView? {
            return scrollView.viewForZooming()
        }

        // Just a demo. You don't need this.
        func scrollViewDidScroll(scrollView: MyScrollView) {
            scrollView.didScroll()
            _userDelegate?.scrollViewDidScroll?(scrollView)
        }
    }

    private var _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 {
            self._delegateProxy._userDelegate = newValue;
            /* It seems, we don't need this anymore.
            super.delegate = nil
            super.delegate = _delegateProxy
            */
        }
    }

    func viewForZooming() -> UIView? {
        println("self viewForZooming")
        return self.subviews.first as? UIView // whatever
    }

    func didScroll() {
        println("self didScroll")
    }
}

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