Can't connect IBAction in Xcode

Question

When I drag from a button on the storyboard to my view controller Swift file, I only get the option to insert an Outlet or Outlet Collection.

Similarly, if I create the

Answer 1

I have very similar issue in my Swift project that was driving me mad.

It turned that's it is the problem of mixing custom protocol adoption in extension of UIButton having @IBInspectable property. More details below.

I finally found out that's because I have following code in my project: (copyright goes to Kevin McNeigh: https://www.iphonelife.com/blog/31369/swift-programming-101-mastering-dynamic-type-ios)

protocol DynamicTypeChangeHandler {

    var typeObserver: Bool {get set}
}

extension UIButton: DynamicTypeChangeHandler {
    @IBInspectable var typeObserver: Bool {
        // ...
    }
}

If I remove either protocol adoption from the extension or @IBInspectable keyword, I can again setup actions in Interface Builder. Sheer lunacy. Xcode <3