在UITabBar中更改ViewController时，不会删除IOS UiBarButtoItemn

I have created programmatically 2 UIBarButtonItem from a UIButton. The Nav Controller is in a UITabBar. When I move to another controller in the same UITabBar, these 2 UIBarButton do not get removed. Anyone has an idea on how to delete these 2 UIBarButtonItemI have created programmatically 2 UIBarButtonIt