[listen] Creates listen package by chunhtai · Pull Request #24 · flutter/core-packages

chunhtai · 2026-06-11T22:03:52Z

code are striped from the flutter/flutter with history intact.

The change is in last commit

Add ci harness
rewire memory leak and error handling harness
add examples

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google-cla · 2026-06-11T22:06:49Z

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This introduces the key parts of a paginated data table, not including the built-in pagination features. * Provide more data for the data table demo, so there's data to page. * Introduce a ChangeNotifier class which abstracts out addListener/removeListener/notifyListeners. We might be able to use this to simplify existing classes as well, though this patch doesn't do that. * Introduce DataTableSource, a delegate for getting data for data tables. This will also be used by ScrollingDataTable in due course. * Introduce PaginatedDataTable, a widget that wraps DataTable and only shows N rows at a time, fed by a DataTableSource.

This patch improves some subtle behaviors about the change notifier.

…889) Having this base class lets classes like CustomPainter and DataTableSource be more agnostic as to what's generating the repaints.

Sometimes you have several listenables, but you want to hand them to an API (e.g. CustomPainter) that only expects one.

This lets you use `Listenable.merge` without having to sanitize your incoming list of change notifiers, in case your semantics are that they are optional.

* MultiTapGestureRecognizer previously would assert if there was no competition. * GestureArenaTeam would always select the first recongizer as the winner even if a later recognizer actually accepted the pointer sequence. * debugPrintStack would fail a type check if maxFrames was non-null. * FractionalOffset.lerp would throw a null-pointer exception if its second argument was null. Also, add a number of tests for previously untested lines of code.

It took me a while to figure out what was going on (I was removing a listener after disposal). These asserts helped.

This patch aligns the iteration patterns used by animations and ChangeNotifier. They now both respect re-entrant removal of listeners and coalesce duplication registrations. (Also, ChangeNotifier notification is no longer N^2). Fixes #7533

This patch aligns the iteration patterns used by animations and ChangeNotifier. They now both respect re-entrant removal of listeners and coalesce duplication registrations. (Also, ChangeNotifier notification is no longer N^2). This patch introduces ObserverList to avoid the performance regression that the previous version of this patch caused. Fixes #7533

Fixes for: flutter/flutter#7570 flutter/flutter#7231 flutter/flutter#2841 and others

It's common to have a ChangeNotifier that wraps a single value. This class makes that easy by providing a generic implementation.

* Change foundation references to meta * Remove specified shows

After this patch, there are three major text input widgets: * EditableText. This widget is a low-level editing control that interacts with the IME and displays a blinking cursor. * TextField. This widget is a Material Design text field, with all the bells and whistles. It is highly configurable and can be reduced down to a fairly simple control by setting its `decoration` property to null. * TextFormField. This widget is a FormField that wraps a TextField. This patch also replaces the InputValue data model for these widgets with a Listenable TextEditingController, which is much more flexible. Fixes #7031

…e method. (#10871) * Change all instances of '$runtimeType#$hashCode' to use the describeIdentity method. The describeIdentity method generates a shorter description with a consistent length consisting of the runtime type and the a 5 hex character long truncated version of the hash code.

…idAndType method. (#10871)" (#10880) This reverts commit d6afe09.

…eIdentity (#10888) * Revert "Revert "Change all ocurrences of '$runtimeType#$hashCode' to use the idAndType method. (#10871)" (#10880)" This reverts commit 7ccc66f.

Add Diagnosticable base class and documentation

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once. This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

* Fix the confusing-zero case with NestedScrollView. * Update mock_canvas.dart * Update tabs_demo.dart * more tweaks

I found that some ValueListeners want to know when they should start doing work (e.g. if the value comes from polling a network resource).

stuartmorgan-g

I only looked at the changes to fit into the repo structure; someone more familiar with the intended usage and the migration plan for clients should definitely review the package API itself.

stuartmorgan-g · 2026-06-29T14:51:07Z

+description: A lightweight synchronous listener registry for pure Dart applications.
+repository: https://github.com/flutter/core-packages/tree/main/packages/listen
+issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+listen%22
+version: 0.1.0


It looks like someone published a placeholder package as 1.0.0-beta, which is going to make publishing a 0.x release confusing.

stuartmorgan-g · 2026-06-29T14:53:47Z

+
+/// Demonstrates [ValueNotifier] usage for README.
+// #docregion ValueNotifier
+void valueNotifierExample() {


Is there a reason this is duplicated almost exactly here from main.dart, instead of the README snippet just pulling from main.dart?

That will require adding the #docregion identifier on the main.dart, which I think may be confusing for people looking at the example. so I intentionally group all excerpt related code in one file even if I can probably grab the code from some other example. Let me know reducing duplication here is more preferred.

Traditionally we haven't worried about having it in main.dart, and only use readme_excerpts.dart when there were things we wanted to show in the README that weren't in the example.

It's not a rule though, so if you are concerned about the comments in the example this is fine.

I will keep this as-is

loic-sharma · 2026-06-29T17:19:30Z

+  }
+}
+
+/// Demonstrates [ChangeNotifier] usage for README.


Nit: can we remove this line? Or could we split this into two excerpts so that we can skip this line?

loic-sharma · 2026-06-29T17:34:16Z

+
+# listen
+
+A lightweight synchronous listener registry for pure Dart applications.


This line feels a little abstract and might be difficult to understand if you have no context. What do you think of this instead?

Suggested change

A lightweight synchronous listener registry for pure Dart applications.

A package to notify state changes to interested listeners.

loic-sharma · 2026-07-02T23:51:48Z

+
+  group('readme excerpts', () {
+    test('valueNotifierExample runs without error', () {
+      expect(readme_excerpts.valueNotifierExample, returnsNormally);


Can we do Zone magic here to check what is printed? That'll ensure that when users run the samples, the output they see matches the comments.

loic-sharma

This looks good to me, but please also get an approval from Stuart :)

stuartmorgan-g · 2026-07-06T14:55:42Z

@@ -0,0 +1,3 @@
+## 1.0.0-beta.1
+
+- Moves source code from `flutter/flutter` to `flutter/core-packages`.


This isn't just a move, it's an extraction as a stand-alone package. We should clarify what the full scope of the change is.

I just realized that changing this would require a new CLA override. Feel free to just adjust in in the next PR to this package.

updated since i will have to squash new commits into a single one and will require a CLA override anyway

stuartmorgan-g · 2026-07-06T14:56:22Z

@@ -0,0 +1,3 @@
+## 1.0.0-beta.1


We never do releases like this, so I'm not entirely sure our CI will handle it correctly. It looks like presubmit is fine, so fingers crossed, but be sure to verify that publishing actually worked after it lands.

stuartmorgan-g · 2026-07-06T14:58:39Z

I've submitted a CLA override for the import, using the usual explanation of this being an import from another repo in the same org that already enforced the CLA on these contributions.

chunhtai · 2026-07-07T02:45:17Z

@stuartmorgan-g , I may need some help to merge this with merge commit to preserve the history.

stuartmorgan-g · 2026-07-07T15:12:12Z

@chunhtai Is it ready to land? If so I can adjust the settings and merge it.

rrousselGit · 2026-07-07T15:20:00Z

+  ///
+  /// By default, errors are thrown as [StateError].
+  static ErrorCallback onError = (String message, StackTrace? stackTrace) {
+    throw StateError(message);


Would it make sense to instead use Zone.current.handleUncaughtError and send back the original err/stack?

I am not sure whether Zone.current.handleUncaughtError is the best way to handle this as it handles the error async, thus won't halt immediately. I do agree the original stack should be preserve somehow. I will handle this as a follow up after this pr

chunhtai · 2026-07-07T22:06:21Z

@stuartmorgan-g yes, this is ready to land

chunhtai · 2026-07-07T22:40:55Z

https://github.com/flutter/core-packages/actions/runs/28903568477/job/85745682204

Hixie and others added 29 commits June 25, 2026 18:39

Improve change notifier (#4747)

ddb441d

This patch improves some subtle behaviors about the change notifier.

Extract a Listenable base class from Animation and ChangeNotifier (#5…

70d66bc

…889) Having this base class lets classes like CustomPainter and DataTableSource be more agnostic as to what's generating the repaints.

Listenable.merge (#7256)

b928281

Sometimes you have several listenables, but you want to hand them to an API (e.g. CustomPainter) that only expects one.

Allow nulls in Listenable.merge (#7355)

23dda28

This lets you use `Listenable.merge` without having to sanitize your incoming list of change notifiers, in case your semantics are that they are optional.

Add more asserts and docs to ChangeNotifier. (#7513)

ed19257

It took me a while to figure out what was going on (I was removing a listener after disposal). These asserts helped.

Revert "Strengthen animation listener iteration patterns" (#7552)

9be184a

Various documentation fixes. (#7726)

f758e93

Fixes for: flutter/flutter#7570 flutter/flutter#7231 flutter/flutter#2841 and others

Add ValueNotifier (#8463)

4adb1f3

It's common to have a ChangeNotifier that wraps a single value. This class makes that easy by providing a generic implementation.

Animation Demo performance tweaks (#8586)

3a4717c

Remove imports of meta (#9081)

cea97ac

Change foundation references in foundation to meta (#9107)

aa8474e

* Change foundation references to meta * Remove specified shows

Better toStrings for Listenable subclasses (#9244)

5b6a595

Simplify change notifier toString and handle nulls (#9368)

75fd887

More docs. (#10214)

2521f2e

More documentation (#10589)

1d927b5

Revert "Change all ocurrences of '$runtimeType#$hashCode' to use the …

f3fe60a

…idAndType method. (#10871)" (#10880) This reverts commit d6afe09.

Change all occurrences of '$runtimeType#$hashCode' to use the describ…

0370c2c

…eIdentity (#10888) * Revert "Revert "Change all ocurrences of '$runtimeType#$hashCode' to use the idAndType method. (#10871)" (#10880)" This reverts commit 7ccc66f.

Add Diagnosticable base class and add documentation. (#11458)

bd4b999

Add Diagnosticable base class and documentation

use bool in assert (#12170)

02e2d32

Fix the confusing-zero case with NestedScrollView. (#14133)

8aa7aca

* Fix the confusing-zero case with NestedScrollView. * Update mock_canvas.dart * Update tabs_demo.dart * more tweaks

some whitespace cleanup (#14443)

f9d12c6

Add a hasListeners to ChangeNotifier (#14946)

c8ae2f8

I found that some ValueListeners want to know when they should start doing work (e.g. if the value comes from polling a network resource).

chunhtai force-pushed the create-listen-package branch from 2118fe9 to a2354b4 Compare June 28, 2026 09:52

kevmoo mentioned this pull request Jun 29, 2026

Move useful Flutter types out of Flutter flutter/flutter#149466

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stuartmorgan-g reviewed Jun 29, 2026

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loic-sharma reviewed Jun 29, 2026

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Comment thread packages/listen/lib/listen.dart Outdated

loic-sharma reviewed Jun 29, 2026

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Comment thread packages/listen/example/test/example_test.dart

loic-sharma reviewed Jun 29, 2026

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Comment thread packages/listen/lib/src/listen.dart

Piinks added the triage-framework Should be looked at in framework triage label Jun 29, 2026

github-actions Bot removed the triage-framework Should be looked at in framework triage label Jul 1, 2026

chunhtai force-pushed the create-listen-package branch from ecf0f23 to da26a37 Compare July 1, 2026 02:02

chunhtai requested review from loic-sharma and stuartmorgan-g July 1, 2026 02:07

jellynoone mentioned this pull request Jul 2, 2026

pkg:listen – hopefully schultek/jaspr#461

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loic-sharma reviewed Jul 2, 2026

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loic-sharma approved these changes Jul 2, 2026

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stuartmorgan-g approved these changes Jul 6, 2026

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Piinks added the triage-framework Should be looked at in framework triage label Jul 6, 2026

Adds listenable package

0be3949

chunhtai force-pushed the create-listen-package branch from da26a37 to 0be3949 Compare July 7, 2026 02:43

github-actions Bot removed the triage-framework Should be looked at in framework triage label Jul 7, 2026

rrousselGit reviewed Jul 7, 2026

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stuartmorgan-g merged commit f4eaec3 into flutter:main Jul 7, 2026
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github-actions Bot added triage-framework Should be looked at in framework triage p: listen labels Jul 7, 2026


		# listen

		A lightweight synchronous listener registry for pure Dart applications.

	A lightweight synchronous listener registry for pure Dart applications.
	A package to notify state changes to interested listeners.

		@@ -0,0 +1,3 @@
		## 1.0.0-beta.1

		- Moves source code from `flutter/flutter` to `flutter/core-packages`.

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stuartmorgan-g commented Jul 6, 2026

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