flet navigationbar - modified sample includes change function - how to simulate navigating between pages via on_change function

flet-navigationbar.py

# modified sample includes change function
# flet v0.11.0
# sample source: https://flet.dev/docs/controls/navigationbar/
import flet as ft


def main(page: ft.Page):
    page.title = "NavigationBar Example"

    page_one_ui = ft.Text("Page One")

    page_two_ui = ft.Text("Page Two")

    page_three_ui = ft.Text("Page Three")

    content = ft.Column([page_one_ui])

    def change_index(e):
        index = page.navigation_bar.selected_index
        print(str(index))

        if index == 0:
            content.controls.pop()
            content.controls.append(page_one_ui)

        if index == 1:
            content.controls.pop()
            content.controls.append(page_two_ui)
        if index == 2:
            content.controls.pop()
            content.controls.append(page_three_ui)

        page.update()

    page.navigation_bar = ft.NavigationBar(
        on_change=change_index,
        destinations=[
            ft.NavigationDestination(
                icon=ft.icons.EXPLORE,
                label="Explore",
            ),
            ft.NavigationDestination(
                icon=ft.icons.COMMUTE,
                label="Commute",
            ),
            ft.NavigationDestination(
                icon=ft.icons.BOOKMARK_BORDER,
                selected_icon=ft.icons.BOOKMARK,
                label="Explore",
            ),
        ],
    )
    page.add(content)


ft.app(target=main)