Keep both NSSplitViewController's child controllers in first responder chain

Question

I\'ve a document based app with an NSSplitViewController as the main window\'s content view controller. The left pane contains a custom view with controller, which implement

Answer 1

In Swift 4 you can do the following:

override func supplementalTarget(forAction action: Selector, sender: Any?) -> Any? {
    for childViewController in childViewControllers {
        if childViewController.responds(to: action) {

            return childViewController
        } else {
            guard let supplementalTarget = childViewController.supplementalTarget(forAction: action, sender: sender) else {
                continue
            }

            return supplementalTarget
        }
    }

    return super.supplementalTarget(forAction: action, sender: sender)
}