The ListView cannot be built in UserControl. Once the ListView is added, other controls will not be displayed

[modaye]

class Sidebar(UserControl):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # self.menu = ListView(expand=1, spacing=10, padding=10, auto_scroll=True, )

    def build(self):
        menu = ListView(
            controls=[
                Text("Select a box", color="#232324"),
            ]
        )
        return Column(
            controls=[
                Text("Sidebar"),
                menu
            ]
        )


def main(page: Page):
    page.title = "Auto-scrolling ListView"
    # page.show_semantics_debugger = True
    sidebar = Sidebar()
    page.add(sidebar)
    page.update()


flet.app(target=main)

The above is a minimum example

[FeodorFitsner]

A working example using expand:

import flet
from flet import Column, ListView, Page, Text, UserControl


class Sidebar(UserControl):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # self.menu = ListView(expand=1, spacing=10, padding=10, auto_scroll=True, )

    def build(self):
        self.expand = True
        menu = ListView(
            controls=[
                Text("Select a box", color="#232324"),
            ],
            expand=True,
        )
        return Column(controls=[Text("Sidebar"), menu])


def main(page: Page):
    page.title = "Auto-scrolling ListView"
    sidebar = Sidebar()
    page.add(sidebar)


flet.app(target=main)

[FeodorFitsner]

Internal notes: We should prevent user errors like that by checking outer bounds for ListView and other scrollable controls.
The following error is generated on Flutter side:

════════ Exception caught by rendering library ═════════════════════════════════
The following assertion was thrown during performResize():
Vertical viewport was given unbounded height.

Viewports expand in the scrolling direction to fill their container. In this case, a vertical viewport was given an unlimited amount of vertical space in which to expand. This situation typically happens when a scrollable widget is nested inside another scrollable widget.

If this widget is always nested in a scrollable widget there is no need to use a viewport because there will always be enough vertical space for the children. In this case, consider using a Column or Wrap instead. Otherwise, consider using a CustomScrollView to concatenate arbitrary slivers into a single scrollable.

The relevant error-causing widget was
ListView

[modaye]

ok, how get the error in flet

[FeodorFitsner]

We have to implement that, not you.

[hololeo]

"Vertical viewport was given unbounded height."

This is why i think getting intrinsic data about the widget at runtime is necessary. flet is not providing enough container properties for flutter to compute layouts (unless they are explicitly set of course) an api call should be provided to have flet query the dart side for all the properties in that widget and the tree. hope that makes sense