This PR introduces a new boolean flag, `isMomentary`, to the
`CupertinoSlidingSegmentedControl` widget.
When `isMomentary` is set to `true`, the segmented control behaves like
a momentary switch. Selecting a segment triggers its associated action
(e.g., via `onValueChanged`), but the segment doesn't stay visually
selected after the interaction ends. The control visually returns to its
previous state or a default state (often no segment selected).
When `isMomentary` is `false` (the default behavior), the control
maintains the selection state visually, highlighting the last chosen
segment.
**Motivation**
Currently, `CupertinoSlidingSegmentedControl` always maintains a
selected state. There are use cases where developers might want to use
the segmented control purely for triggering actions without persisting a
visual selection state, similar to how a `UISegmentedControl` can be
configured on iOS with `isMomentary = true`. This provides more
flexibility and aligns the Flutter widget closer to its native
counterpart's capabilities.
For example, this could be useful for triggering sorting actions, view
changes, or other immediate operations where maintaining a persistent
"selected" state isn't desired or meaningful.
**Related Issues**
fixes: #164077
**Videos**
UISegmentedControl behaviour when `isMomentary` flag is set to true.
https://github.com/user-attachments/assets/84d00312-4530-4b7a-9696-142f60ad89c0
CupertinoSlidingSegmentedControl behaviour when `isMomentary` flag is
set to true.
https://github.com/user-attachments/assets/b308b4fa-e641-417a-a518-4e0908876eed
## Pre-launch Checklist
- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.
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**Reviewers:** Please carefully review all the commits except for the
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---------
Co-authored-by: Kate Lovett <katelovett@google.com>
Co-authored-by: LongCatIsLooong <31859944+LongCatIsLooong@users.noreply.github.com>
