https://github.com/user-attachments/assets/59225cf7-5506-414e-87da-aa4d3227e7f6
Adds:
* `SelectionListener`, allows a user to listen to selection changes
under the subtree it wraps given their is an ancestor `SelectionArea` or
`SelectableRegion`. These selection changes can be listened to through
the `SelectionListenerNotifier` that is provided to a
`SelectionListener`.
* `SelectionListenerNotifier`, used with `SelectionListener`, allows a
user listen to selection changes for the subtree of the
`SelectionListener` it was provided to. Provides access to individual
selection values through the `SelectionDetails` object `selection`.
* `SelectableRegionSelectionStatusScope`, allows the user to listen to
when a parent `SelectableRegion` is changing or finalizing the
selection.
* `SelectedContentRange`, provides information about the selection range
under a `SelectionHandler` or `Selectable` through the `getSelection()`
method. This includes a start and end offset relative to the
`Selectable`s content.
* `SelectionHandler.contentLength`, to describe the length of the
content contained by a selectable.
Original PR & Discussion: https://github.com/flutter/flutter/pull/148998Fixes: #110594
## 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.
---------
Co-authored-by: Renzo Olivares <roliv@google.com>
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