feature: Add on-demand getters/methods for scroll position (offset) and max_scroll_extent in ListView

[Iaw4tch]

Duplicate Check

• I have searched the opened issues and there are no duplicates

Describe the requested feature

Currently, if I need to know current scroll position (pixels) or its max value (max_scroll_extent) of ListView, the only way to do this is to track on_scroll: there's where a huge problem rises.

If I want to get these variables for the first time, i need a user to trigger the event or do it programmatically with scroll_to method. Moreover even with that you need to listen to this event all the time, save needed to the local variables and constantly synchronize them. It complicates the logic and loads the app with intermediate events.

Suggest a solution

The solution is quite simple: make an asynchronous getter/method of ListView that returns scroll offset or max extent.

Screenshots

No response

Additional details

I am creating a custom class InertiaListView (a wrapper of GestureDetector), which allows to drag ListView up and down with inertia on_pan_end.

class InertiaListView(ft.GestureDetector):
    def __init__(
        self,
        controls: list[ft.Control],
        smoothness_time: float = 0.00001,
        inertia_duration: float = 1,
        stop_velocity: float = 30,
        expand: bool | int | None = None,
        alignment: ft.Alignment | None = None,
    ):
        ...
        self._list_view = ft.ListView(
            spacing=10,
            scroll=ft.ScrollMode.AUTO,
            on_scroll=self._on_scroll,
            animate_offset=ft.Animation(duration=0),
            controls=controls,
        )


        super().__init__(
            expand=expand,
            on_pan_start=self._on_pan_start,
            on_pan_update=self._on_pan_update,
            on_pan_end=self._on_pan_end,
            content=ft.Container(
                expand=True,
                alignment=alignment,
                content=self._list_view,
            ),
        )

        self._max_offset: float = 0.01
        self._current_offset: float = 0

    def _on_scroll(self, e: ft.OnScrollEvent):
        if self._max_offset != e.max_scroll_extent:
            self._max_offset = e.max_scroll_extent if e.max_scroll_extent != 0 else 0.01

        self._current_offset = e.pixels

I need self._current_offset for the safety in the mismatch of my variable, and the true one.

self._max_offset is used to track the bounds of the offset:

def _clamp_offset(self, offset: float):
    if not 0 <= offset <= self._max_offset:
        self._velocity = 0

    return max(0.0, min(offset, self._max_offset))

My code would become cleaner if there was an option to asynchronously get the these ListView properties.

[Iaw4tch]

this may be added not only to things i need, but to all properties like these.

on_scroll pushes me all the data on every scroll. Spot pull allows to get rid of the overhead