Fix Expansible crash when PageStorage holds a non-bool value by omar-alshyokh · Pull Request #192195 · flutter/flutter

omar-alshyokh · 2026-09-02T18:26:13Z

Description

Expansible reads and writes its expansion state in PageStorage. The slot it uses is picked from the PageStorageKeys above it in the tree. An Expansible with no key of its own lands in the slot of some ancestor key and shares it with other widgets, such as a Scrollable that saves a double there. Reading that value with as bool? threw:

type 'double' is not a subtype of type 'bool?' in type cast
  _ExpansibleState.initState (expansible.dart)

The same collision goes the other way. The Expansible writes a bool into that slot, and ScrollPosition.restoreScrollOffset then throws reading it as double?.

Changes:

Expansible saves its state under an identifier of its own, built from the PageStorageKeys above it, so it never shares a slot with other widgets under the same keys.
ScrollPosition.restoreScrollOffset and _PagePosition.restoreScrollOffset only use the stored value if it is a double.

Related issue

Fixes #192184

Thanks to @FabriceLeger for reporting it with the exact crash location.

Tests

Added to expansible_test.dart: a non-bool value in the slot, an unkeyed Expansible in a keyed ListView (the scroll offset is not overwritten), a keyed Expansible containing a Scrollable (both keep their state), and a key on the parent (state is kept). Added to page_view_test.dart and scroll_position_test.dart: a non-double value in the slot. Each fails without the fix and passes with it.

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I added new tests to check the change I am making, or this PR is test-exempt.
I followed the breaking change policy and added Data Driven Fixes where supported.
All existing and new tests are passing.

PageStorage is untyped and the same bucket slot can be written by other widgets, such as a Scrollable that saves a double offset. Expansible read that slot with a bool cast, which threw a type error when the stored value was not a bool. Read the value first and only use it when it is a bool, otherwise fall back to the controller's state. Fixes flutter#192184

gemini-code-assist · 2026-09-02T18:26:30Z

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victorsanni

Thanks for the PR. I don't think modifying the guards alone is the right solution. On a high level I don't think Expansible should just arbitrarily read bools from PageStorage.

My intuition is Expansible should only read from and write to PageStorage if there is a PageStorageKey associated with the Expansible itself (or if the key is on an ancestor like ExpansionTile.

What do you think?

victorsanni · 2026-09-17T20:05:01Z

-    final bool initiallyExpanded =
-        PageStorage.maybeOf(context)?.readState(context) as bool? ?? widget.controller.isExpanded;
+    // PageStorage is untyped and the same slot can be written by other widgets,
+    // such as a Scrollable that saves a double. Only use the stored value if it


This fixes the crash in Expansible, but not potential crashes in the Scrollable.

ExpansibleState._toggleExpansion writes a bool to PageStorage. But ScrollPositionWithSingleContext.restoreScrollOffset reads the page storage value as a double, which can cause basically the same crash as this one but in the reverse direction. An easy way to repro this is to create an Expansible with a key and have its body contain a Scrollable:

import 'package:flutter/material.dart'; void main() => runApp(const MyApp()); class MyApp extends StatelessWidget { const MyApp({super.key}); @override Widget build(BuildContext context) { return MaterialApp( home: Scaffold( appBar: AppBar(title: const Text('Tap the tile to crash')), body: const ExpansionTile( key: PageStorageKey<String>('my_tile'), title: Text('Tap me to expand'), children: <Widget>[ SingleChildScrollView( child: Text('Scrollable content inside ExpansionTile'), ), ], ), ), ); } }

At minimum we should also fix this in this PR. (side note, _PagePosition.restoreScrollOffset does the same thing too).

omar-alshyokh · 2026-09-18T06:11:25Z

@victorsanni Agreed, an unkeyed Expansible should not touch PageStorage at all. I also hit the reverse crash you mentioned. An unkeyed Expansible inside a keyed ListView overwrites the saved scroll offset with a bool, and the list crashes the next time it is built and restores the offset. Your sample crashes on the first tap.

Gating on the key does not cover the keyed case though, since a Scrollable inside the tile still shares the slot. So I am thinking:

Expansible only uses PageStorage if its own key or its parent's key is a PageStorageKey. The parent check is for ExpansionTile, which cannot change under the Material freeze.
restoreScrollOffset in ScrollPosition and _PagePosition only uses the value if it is a double.
Keep the type check on the Expansible read.
Add the two tests you listed, plus one for the overwritten scroll offset.

Does checking the parent's key work for you, or should Expansible only look at its own key?

An Expansible without a PageStorageKey of its own, or on its parent, ends up in the slot of some ancestor key and collides with other widgets there, such as a Scrollable. Skip PageStorage in that case. Also make ScrollPosition and _PagePosition ignore a stored value that is not a double, since a keyed Expansible can share a slot with a Scrollable inside it.

omar-alshyokh · 2026-09-23T11:48:58Z

@victorsanni Pushed the changes.

Expansible only reads and writes PageStorage when its own key or its parent's key is a PageStorageKey. I went with the parent check so a key on ExpansionTile keeps working, since that file cannot change under the freeze.
ScrollPosition.restoreScrollOffset and _PagePosition.restoreScrollOffset only use the stored value if it is a double.
Added tests for an unkeyed Expansible in a keyed ListView, a keyed Expansible containing a Scrollable, a key on the parent, a key further up the tree, and a PageView reading a non-double. Your sample passes now.

victorsanni

Thanks for the updates.

This approach feels very brittle overall, it is very dependent on the shape of the widget tree. So if an ExpansionTile for example wraps its Expansible in another widget, it would break. Also it is naive, the Expansible doesn't care what its parent is.

Is it possible to have a unique identifier attached to readState and writeState to ensure we are only using Expansible keys?

Expansible shared its PageStorage slot with other widgets under the same PageStorageKeys, such as a Scrollable, so the two overwrote each other and crashed on read. Save the expansion state under an identifier of its own instead.

omar-alshyokh · 2026-09-25T12:15:39Z

@victorsanni Pushed. Expansible now saves its state under an identifier of its own, built from the PageStorageKeys above it, so it never shares a slot with a Scrollable and a key on ExpansionTile keeps working. No parent check anymore. The keyed tile test checks that both the tile and the Scrollable inside it keep their state, and the Expansible docs say so too.

victorsanni · 2026-09-28T18:54:31Z

Hi, please remember to re-request a review when you have made changes to your PRs, so it can re-enter my review queue. Else I don't see that your PR has been updated and can't leave a review.

auto-submit · 2026-10-08T19:59:31Z

autosubmit label was removed for flutter/flutter/192195, because - The status or check suite Google testing has failed. Please fix the issues identified (or deflake) before re-applying this label.

omar-alshyokh · 2026-10-09T05:31:22Z

Thanks @victorsanni and @Mairramer for the approvals! I see Google testing failed. I can't see the internal logs, so if you can share what failed, I'm happy to fix it on my side.

omar-alshyokh · 2026-10-12T09:42:59Z

@victorsanni Good news, Google testing passed on the re-run. Could you add the autosubmit label again when you have a moment? Thanks a lot for all the help on this one!

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@FabriceLeger

…#192195) ## Description `Expansible` reads and writes its expansion state in `PageStorage`. The slot it uses is picked from the `PageStorageKey`s above it in the tree. An `Expansible` with no key of its own lands in the slot of some ancestor key and shares it with other widgets, such as a `Scrollable` that saves a `double` there. Reading that value with `as bool?` threw: ``` type 'double' is not a subtype of type 'bool?' in type cast _ExpansibleState.initState (expansible.dart) ``` The same collision goes the other way. The `Expansible` writes a `bool` into that slot, and `ScrollPosition.restoreScrollOffset` then throws reading it `as double?`. Changes: - `Expansible` saves its state under an identifier of its own, built from the `PageStorageKey`s above it, so it never shares a slot with other widgets under the same keys. - `ScrollPosition.restoreScrollOffset` and `_PagePosition.restoreScrollOffset` only use the stored value if it is a `double`. ## Related issue Fixes flutter#192184 Thanks to @FabriceLeger for reporting it with the exact crash location. ## Tests Added to `expansible_test.dart`: a non-bool value in the slot, an unkeyed `Expansible` in a keyed `ListView` (the scroll offset is not overwritten), a keyed `Expansible` containing a `Scrollable` (both keep their state), and a key on the parent (state is kept). Added to `page_view_test.dart` and `scroll_position_test.dart`: a non-double value in the slot. Each fails without the fix and passes with it. ## 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 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. [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md --------- Co-authored-by: Mairramer <[email protected]> Co-authored-by: Victor Sanni <[email protected]>

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_ExpansibleState.initState + 383 type 'double' is not a subtype of type 'bool?' in type cast #192184

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Comment thread packages/flutter/lib/src/widgets/expansible.dart Resolved

Use a switch expression for the stored expansion state

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Merge branch 'master' into fix-expansible-non-bool-pagestorage

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Comment thread packages/flutter/lib/src/widgets/scroll_position.dart Resolved

Comment thread packages/flutter/lib/src/widgets/page_view.dart Resolved

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Merge branch 'master' into fix-expansible-non-bool-pagestorage

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Add a namespace to PageStorageBucket readState and writeState #194315

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Roll Flutter from d03768eef055 to a4896bac0e8f (201 revisions) flutter/packages#13254

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Roll Flutter from 4249ccbc18a3 to 426be968b5eb (44 revisions) flutter/packages#13256

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