NavigationRail not displayed when returned by build method

[clstaudt]

As shown in the ToDoApp tutorial, I would like to create a class representing the main application (window). This application should have a side bar containing a NavigationRail. The problem: When the NavigationRail is returned by the build method of the App class (rather than added to the page directly), it is not displayed.

(In general it would be great to have a code example or template for how to implement such a common app window layout - sidebar and main window area changing depending on sidebar selection - with flet.)

import flet
from flet import (
    UserControl,
    Page,
    View,
    Text,
    Column,
    Row,
    KeyboardEvent,
    SnackBar,
    NavigationRail,
    NavigationRailDestination,
    VerticalDivider,
    Icon,
)
from flet import icons

from tuttle.controller import Controller

from views import (
    ContactView,
)

class App(UserControl):
    """Main application window."""

    def __init__(
        self,
    ):
        super().__init__()

    def build(self):
        return Row(
            [
                NavigationRail(
                    destinations=[
                        NavigationRailDestination(
                            icon=icons.AREA_CHART_OUTLINED,
                            selected_icon=icons.AREA_CHART,
                            label="Dashboard",
                        )
                    ],
                    extended=True,
                ),
                VerticalDivider(width=1),
            ]
        )


def main(page: Page):

    app = App()

    page.add(
        app,
    )

    page.update()


flet.app(
    target=main,
)

[FeodorFitsner]

Closing in favor of #303