bug: Declarative app: When child controls don't have unique keys, the list is displayed incorrectly after deleting an item

[InesaFitsner]

Duplicate Check

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

Describe the bug

In example, each ft.Dismissible is rendered without a unique key. After swiping an item away, the list is displayed with 2 items removed instead of one. The issue is fixed if uncomment key.

Code sample

Code

import flet as ft


@ft.component
def App():
    items, set_items = ft.use_state(list(range(5)))

    return ft.ListView(
        controls=[
            ft.Dismissible(
                # key=i,
                content=ft.ListTile(title=ft.Text(f"Item {i}")),
                dismiss_direction=ft.DismissDirection.HORIZONTAL,
                background=ft.Container(bgcolor=ft.Colors.GREEN),
                secondary_background=ft.Container(bgcolor=ft.Colors.RED),
                on_dismiss=lambda e, index=i: set_items(
                    [item for item in items if item != index]
                ),
                dismiss_thresholds={
                    ft.DismissDirection.HORIZONTAL: 0.1,
                    ft.DismissDirection.START_TO_END: 0.1,
                },
            )
            for i in items
        ],
    )


ft.run(lambda page: page.render_views(App))

To reproduce

1. run example
2. swipe to dismiss any item -> the dismissed row vanishes momentarily, as well as the other row that should stay

Expected behavior

once an item is dismissed, the remaining tiles realign to match the updated items state.

Screenshots / Videos

Captures

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Operating System

macOS

Operating system details

macOS

Flet version

0.69.0

Regression

No, it isn't

Suggestions

No response

Logs

Logs

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Additional details

No response

[FeodorFitsner]

The issue is specific to Dismissible control. When a user swipe the first element it becomes "dismissed" on Flutter side and the element is being deleted from the list. However, without key, when Flet calculates the difference it produces change commands like "update text value in elements 0..N-1 and then delete the last element N". On Flutter side though Dismissible widget in the middle of the list cannot be updated as it's "dismissed" already, hence the error.
Always use key for Dismissible.