Swift protocol extension not being called

Question

I tried to make a default implementation of protocol UIScrollViewDelegate, for example:

extension UIScrollViewDelegate {
     func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
         //...
     }
}

But In a subclass UITableViewController (which conforms to UIScrollViewDelegate and) does not contain any implementation this method (neither in base class nor in subclass), this extension-provided implementation won't be called

Is there any solution to provide a default implementation for these methods?

Lukas Würzburger · Answer 1 · 2018-02-19T14:13:47.263

2

Just create an extension of UIScrollView to conform to UIScrollViewDelegate protocol like this:

extension UIScrollView: UIScrollViewDelegate {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // ...
    }
}

edited Feb 19 '18 at 14:13

answered Feb 19 '18 at 14:07

Lukas Würzburger

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This doesn't work though. – Petar Oct 27 '20 at 17:01

score 1 · Accepted Answer · answered Feb 19 '18 at 14:23

You are trying to make a Swift protocol extension on an Objective-C protocol. That's never going to work, because Objective-C cannot see a Swift protocol extension, so Cocoa (which is Objective-C) will never know about your implementation and will never call it.

Swift protocol extension not being called

2 Answers2