left_button_items are added to the title bar rather than the navigation bar.
nav = ui.NavigationView(v) nav.left_button_items = [ui.ButtonItem(title='Hi')]
The buttons that appear on the navigation view toolbar (the one with the back button) come from the view that's currently visible in the navigation view. That means you need to set the
nav. When you push/pop views on
nav, the toolbar buttons change to those of the new top view.