feat: Programmatically expand/collapse ExpansionTile

[ndonkoHenri]

Fix #3626

Example

import flet as ft


def main(page: ft.Page):
    page.spacing = 20

    def expand_tile(e: ft.Event[ft.FilledButton]):
        tile.expanded = True

    def collapse_tile(e: ft.Event[ft.OutlinedButton]):
        tile.expanded = False

    page.add(
        ft.Row(
            alignment=ft.MainAxisAlignment.CENTER,
            controls=[
                ft.FilledButton("Expand Tile", on_click=expand_tile),
                ft.OutlinedButton("Collapse Tile", on_click=collapse_tile),
            ],
        ),
        tile := ft.ExpansionTile(
            title=ft.Text("I am the title of this tile.", weight=ft.FontWeight.BOLD),
            subtitle=ft.Text("This is the subtitle."),
            affinity=ft.TileAffinity.LEADING,
            controls=[ft.Text("👻", size=80)],
            expanded=True,
            on_change=lambda e: print(
                f"Tile was {'expanded' if e.data else 'collapsed'}"
            ),
        ),
    )


ft.run(main)

Summary by Sourcery

Enable programmatic control of ExpansionTile expansion state and customizable animation behavior.

New Features:

• Introduce an "expanded" property on ExpansionTile for programmatic expand/collapse.
• Add "animation_style" property and AnimationStyle.no_animation() to customize or disable expand/collapse animations.
• Expose on_change event data as a boolean reflecting the tile’s expanded state.

Bug Fixes:

• Fix default selected_index handling and change-event logic in CupertinoSlidingSegmentedButton control.

Enhancements:

• Refactor Dart ExpansionTileControl to a StatefulWidget with an ExpansibleController for safe state updates.
• Augment Python and Dart documentation and examples with sections on programmatic expansion/collapse and custom animations.
• Provide detailed docstrings for TileAffinity, theme properties, and internal control fields.

[sourcery-ai]

We've reviewed this pull request using the Sourcery rules engine

[Copilot]

Pull Request Overview

This PR adds programmatic expansion/collapse functionality to the ExpansionTile control by introducing an expanded property, replacing the previous initially_expanded property which only set the initial state. The implementation includes animation customization support and comprehensive documentation updates.

• Adds expanded property to control tile state programmatically
• Introduces animation_style property for customizing expansion/collapse animations
• Updates documentation with examples and enhanced property descriptions

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
sdk/python/packages/flet/src/flet/controls/material/expansion_tile.py	Adds expanded and animation_style properties, replaces initially_expanded, enhances documentation, and adds validation for CrossAxisAlignment.BASELINE
packages/flet/lib/src/controls/expansion_tile.dart	Converts to StatefulWidget with ExpansibleController to manage programmatic expansion state
sdk/python/packages/flet/src/flet/controls/animation.py	Adds AnimationStyle class documentation and no_animation() static method
sdk/python/packages/flet/src/flet/controls/theme.py	Adds theme properties for ExpansionTile and ListTile including animation_style, shape, collapsed_shape, affinity, style, and title_alignment
sdk/python/examples/controls/expansion_tile/programmatic_expansion.py	New example demonstrating programmatic tile expansion/collapse
sdk/python/examples/controls/expansion_tile/custom_animations.py	New example showing custom animation styles for expansion tile
sdk/python/packages/flet/docs/controls/expansiontile.md	Adds documentation sections for programmatic expansion and custom animations
packages/flet/lib/src/utils/theme.dart	Updates theme parsers to support new ExpansionTile and ListTile theme properties
sdk/python/packages/flet/src/flet/controls/material/text_button.py	Minor documentation wording improvement
sdk/python/packages/flet/src/flet/controls/material/expansion_panel.py	Minor documentation wording improvement
sdk/python/packages/flet/src/flet/controls/cupertino/cupertino_sliding_segmented_button.py	Simplifies documentation and reorders example property
packages/flet/lib/src/controls/cupertino_sliding_segmented_button.dart	Minor code formatting and logic simplification
sdk/python/packages/flet/src/flet/controls/base_control.py	Adds internal documentation for _internals field

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View logs

[FeodorFitsner]

Please fix tests: https://github.com/flet-dev/flet/actions/runs/18736961772
Add tests for introduced/changed functionality:

1. ExpansionTile.expanded = True/False
2. ListTileTheme - new props