Cocoa - finding out when an NSTabView has changed its tabs

Question

How can I find out when a NSTabViewItem has been changed, i.e. a user has changed the view of an NSTabView?

Ideally I want to generate a notification but any solution would be welcome.

Answer 1

My original answer suggested to observe selectedTabViewItem of NSTabView, but that doesn't seem to work (on testing I can only get it to observe NSKeyValueObservingOptionInitial).

A probably smarter solution is to use a delegate. Implement tabView:didSelectTabViewItem: in the relevant controller.

Docs here.

Answer 2

Here is an example in Swift 3.

Create a custom class for your NSTabViewController which acts as delegate of NSTabView. The NSTabViewController class already implements the NSTabViewDelegate protocol.

class CustomTabViewController: NSTabViewController {
    override func tabView(_ tabView: NSTabView, didSelect tabViewItem: NSTabViewItem?) {
        let identifier = tabViewItem?.identifier as? String
        print(identifier)
    }

}

Then in Interface Builder:

1. Assign the custom class you created to your Tab View Controller in the Identity Inspector in the right panel
2. In the interface hierarchy panel on the left, control drag from the Tab View to the Custom Tab View Controller (the name will depend on your custom class) and select delegate from the little popover that appears

You can also implement other methods in your delegate as explained in the documentation of NSTabViewDelegate.