How to avoid calling `awakeFromNib` twice when view uses a separate `xib` for its TouchBar

Question

Background

I'm adding a TouchBar to an app. I have a few window controllers that should use the same TouchBar design, adopt the same protocol (say AddWindowCommon), and are designed in their own xib file.

I designed my TouchBar in a separate xib file (AddWindowTouchBar). This way I can set the file to only compile on macOS 10.12.2+ (the versions that support the TouchBar) while the rest of the project deploys on macOS 10.9+. The file owner adopts the AddWindowCommon protocol and the touchbar keeps a weak reference to it to function properly. Then, to use this touchbar, I override the makeTouchBar as such:

@available(OSX 10.12.2, *)
open override func makeTouchBar() -> NSTouchBar? {
    return AddWindowTouchBar.instanceFromNib(withWindowController: self)
}

That calls the following static function of my AddWindowTouchBar class:

static func instanceFromNib(withWindowController windowController: AddWindowCommon) -> AddWindowTouchBar {
        var objects = NSArray()
        Bundle.main.loadNibNamed(xibName, owner: windowController, topLevelObjects: &objects)

        // ...
        // return the touchbar from `objects`
        // ...

}

Question

The problem here is that a class that adopts the AddWindowCommon protocol has its awakeFromNib: method called twice: a first time when it is loaded from its own xib, and a second time when the AddWindowTouchBar is instantiated using loadNibNamed:owner: and the window controller is the owner.

To avoid performing the tasks in awakeFromNib: twice, I could use a simple boolean that ensures the class hasn't been awakened from a nib yet, but I was wondering if there was another cleaner solution that acted on the AddWindowTouchBar rather than on the AddWindowCommon protocol-adopters.