fix: SnackBar and Banner not opening in cupertino pages

[ndonkoHenri]

Fix #3017

Example

import flet as ft


def main(page: ft.Page):
    page.platform = ft.PagePlatform.MACOS
    page.adaptive = True

    page.add(
        ft.ElevatedButton(
            "Open SnackBar",
            on_click=lambda: page.show_dialog(ft.SnackBar("Hello, World!")),
        )
    )


ft.run(main)

Summary by Sourcery

Fix SnackBar visibility on Cupertino pages and improve responsive layout and segmented button documentation, including new examples and tests.

New Features:

• Add a custom breakpoint ResponsiveRow example demonstrating non-standard breakpoint usage.

Bug Fixes:

• Ensure SnackBar (and other ScaffoldMessenger-based overlays) work correctly on Cupertino pages by injecting a Material ScaffoldMessenger into the app builder.

Enhancements:

• Document ResponsiveRowBreakpoint values and responsive breakpoint configuration more clearly in code and docs.
• Refine segmented button documentation structure, separating Segment docs into their own page and adjusting images and options accordingly.

Documentation:

• Expand ResponsiveRow documentation with a custom breakpoint example and clearer explanations of breakpoint configuration.
• Add a dedicated documentation page for the Segment control and link it from the SegmentedButton docs.

Tests:

• Add an integration test verifying that SnackBar displays correctly on a Cupertino page.

[sourcery-ai]

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

[Copilot]

Pull request overview

This PR fixes an issue where SnackBar and Banner controls were not opening in Cupertino (iOS/macOS style) pages. The fix wraps CupertinoApp with a ScaffoldMessenger widget using the builder parameter, which provides the necessary Material infrastructure for these Material Design components to function in Cupertino apps.

Key changes:

• Added a scaffoldMessengerBuilder function that wraps the app with Material theme and ScaffoldMessenger
• Applied this builder to both CupertinoApp and CupertinoApp.router variants
• Added test coverage for SnackBar in Cupertino pages
• Includes additional documentation improvements for ResponsiveRow and SegmentedButton controls

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/flet/lib/src/controls/page.dart	Core fix: Adds ScaffoldMessenger wrapper to CupertinoApp via builder parameter to enable Material components (SnackBar/Banner) in Cupertino pages
sdk/python/packages/flet/integration_tests/controls/material/test_snack_bar.py	Adds test case to verify SnackBar works in Cupertino pages with adaptive=True
sdk/python/packages/flet/integration_tests/controls/material/golden/macos/snack_bar/cupertino_page.png	Golden screenshot for Cupertino page SnackBar test
sdk/python/packages/flet/src/flet/controls/types.py	Improves documentation for ResponsiveRowBreakpoint enum with detailed descriptions
sdk/python/packages/flet/src/flet/controls/core/responsive_row.py	Enhances documentation for ResponsiveRow.breakpoints property
sdk/python/packages/flet/docs/controls/segmentedbutton.md	Refactors documentation to separate Segment class into its own page
sdk/python/packages/flet/docs/controls/segment.md	Adds dedicated documentation page for Segment class
sdk/python/packages/flet/docs/controls/responsiverow.md	Adds custom breakpoints example section
sdk/python/examples/controls/responsive_row/custom_breakpoint.py	Adds new example demonstrating custom breakpoints usage
sdk/python/examples/controls/responsive_row/basic.py	Updates example to use ResponsiveRowBreakpoint enum instead of string literals
sdk/python/packages/flet/mkdocs.yml	Updates navigation to include Segment as a nested item under SegmentedButton

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