Accessing the UIView of tabBarButtonItem

I need to animate the UIView of a tabBarButton with some fade in. - fade out effect.

I use UIView animation ; to do so, I need to access the UIView of the barButton.

I do it as follows, which works perfectly:

if let buttonView = self.navigationItem.leftBarButtonItem!.value(forKey: "view") as? UIView {

Question: would this be considered as using a private API ?

what I read from h ttps://gist.github.com/ArtSabintsev/8825288) says no problem.

I would appreciate a confirmation.