[iOS] Fix Switch ThumbColor reset on iOS 26+ theme changes. by Shalini-Ashokan · Pull Request #33953 · dotnet/maui

Shalini-Ashokan · 2026-02-09T10:00:36Z

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

On iOS/MacCatalyst 26+, when the app theme changes (light ↔ dark), the Switch's ThumbColor resets to white instead of keeping the custom color.

Root Cause

On iOS/MacCatalyst 26+, UIKit resets the UISwitch's ThumbTintColor to its default value during theme transitions.

Description of Change

Register for trait collection changes to detect theme switches, then re-apply the custom ThumbColor after UIKit completes its styling.

Validated the behavior in the following platforms

Android
Windows
iOS
Mac

Issues Fixed

Fixes #33783
Fixes #33767

Output ScreenShot

Before	After
33783-BeforeFix.mov	33783-AfterFix.mov

sheiksyedm · 2026-02-10T06:50:08Z

/azp run maui-pr-uitests

azure-pipelines · 2026-02-10T06:50:19Z

Azure Pipelines successfully started running 1 pipeline(s).

sheiksyedm · 2026-02-18T11:55:34Z

/rebase

github-actions · 2026-02-27T08:09:43Z

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 33953

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 33953"

Copilot

Pull request overview

Fixes an iOS/MacCatalyst 26+ behavior where UISwitch.ThumbTintColor gets reset during theme (light/dark) changes by re-applying the custom thumb color after trait changes and adding a UI test scenario.

Changes:

Register for UITraitUserInterfaceStyle changes on iOS/MacCatalyst 26+ and re-apply ThumbColor.
Add a delayed re-apply path for thumb color to allow UIKit styling to finish.
Add a new issue page + UI test coverage for the theme-change scenario.

Reviewed changes

Copilot reviewed 3 out of 13 changed files in this pull request and generated 4 comments.

File	Description
src/Core/src/Handlers/Switch/SwitchHandler.iOS.cs	Re-applies thumb color on trait (theme) changes for iOS/MacCatalyst 26+.
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33783.cs	Adds screenshot-based UI tests for switching themes.
src/Controls/tests/TestCases.HostApp/Issues/Issue33783.cs	Adds a host app repro page with theme toggle buttons and a custom-colored switch.

src/Core/src/Handlers/Switch/SwitchHandler.iOS.cs

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33783.cs

kubaflo

Looks like the test succeeds without a fix

sheiksyedm · 2026-03-31T13:15:45Z

/azp run maui-pr-uitests

azure-pipelines · 2026-03-31T13:15:58Z

Azure Pipelines successfully started running 1 pipeline(s).

jfversluis · 2026-04-01T11:36:23Z

/rebase

azure-pipelines · 2026-04-01T11:39:58Z

Azure Pipelines successfully started running 1 pipeline(s).

MauiBot · 2026-04-01T14:19:39Z

🚦 Gate - Test Before and After Fix

📊 Expand Full Gate — 0807361 · committed the windows snapshot

Gate Result: ❌ FAILED

Platform: IOS · Base: main · Merge base: 720a9d4a

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
🖥️ Issue33783 `Issue33783`	❌ PASS — 238s	✅ PASS — 84s

🔴 Without fix — 🖥️ Issue33783: PASS ❌ · 238s

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Build succeeded.

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VSTest version 18.0.1 (arm64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
/Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.04]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.13]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 2 of 2 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 4/1/2026 7:18:01 AM FixtureSetup for Issue33783(iOS)
>>>>> 4/1/2026 7:18:04 AM VerifySwitchThumbColorOnDarkThemeChange Start
>>>>> 4/1/2026 7:18:06 AM VerifySwitchThumbColorOnDarkThemeChange Stop
>>>>> 4/1/2026 7:18:06 AM VerifySwitchThumbColorOnLightThemeChange Start
  Passed VerifySwitchThumbColorOnDarkThemeChange [1 s]
>>>>> 4/1/2026 7:18:06 AM VerifySwitchThumbColorOnLightThemeChange Stop
  Passed VerifySwitchThumbColorOnLightThemeChange [831 ms]
NUnit Adapter 4.5.0.0: Test execution complete

Test Run Successful.
Total tests: 2
     Passed: 2
 Total time: 1.1140 Minutes

🟢 With fix — 🖥️ Issue33783: PASS ✅ · 84s

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VSTest version 18.0.1 (arm64)

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A total of 1 test files matched the specified pattern.
/Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.04]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.13]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 2 of 2 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 4/1/2026 7:19:25 AM FixtureSetup for Issue33783(iOS)
>>>>> 4/1/2026 7:19:29 AM VerifySwitchThumbColorOnDarkThemeChange Start
>>>>> 4/1/2026 7:19:30 AM VerifySwitchThumbColorOnDarkThemeChange Stop
>>>>> 4/1/2026 7:19:30 AM VerifySwitchThumbColorOnLightThemeChange Start
  Passed VerifySwitchThumbColorOnDarkThemeChange [917 ms]
>>>>> 4/1/2026 7:19:31 AM VerifySwitchThumbColorOnLightThemeChange Stop
  Passed VerifySwitchThumbColorOnLightThemeChange [822 ms]
NUnit Adapter 4.5.0.0: Test execution complete

Test Run Successful.
Total tests: 2
     Passed: 2
 Total time: 17.7473 Seconds

⚠️ Issues found

❌ Issue33783 PASSED without fix (should fail) — tests don't catch the bug

📁 Fix files reverted (2 files)

eng/pipelines/ci-copilot.yml
src/Core/src/Handlers/Switch/SwitchHandler.iOS.cs

New files (not reverted):

github-merge-flow-release-11.jsonc

MauiBot · 2026-04-01T16:45:16Z

🤖 AI Summary

📊 Expand Full Review — 39a41f2 · Resolved the gate failures

🔍 Pre-Flight — Context & Validation

Issue: #33783 - Switch ThumbColor not applied correctly when theme changes on iOS (iOS 26+ device only)
Issue2: #33767 - macOS 26+, Switch/button color white by default (related UIKit ThumbTintColor reset)
PR: #33953 - [iOS] Fix Switch ThumbColor reset on iOS 26+ theme changes
Platforms Affected: iOS 26+, MacCatalyst 26+
Files Changed: 1 implementation (SwitchHandler.iOS.cs), 2 test files + 12 snapshot PNGs

Key Findings

Root Cause: On iOS/MacCatalyst 26+, UIKit resets UISwitch.ThumbTintColor to its default (white) during light/dark theme transitions. The fix registers for UITraitUserInterfaceStyle changes via RegisterForTraitChanges<UITraitUserInterfaceStyle> and re-applies the custom ThumbColor after a 10ms async delay.
Gate FAILED: Test passes both with and without the fix. The test page sets ThumbColor = Colors.Red as a direct property — on the iOS simulator, UIKit may not reset ThumbTintColor the same way a real device does (issue Switch ThumbColor not Initialized Using VisualStateManager on iOS Device #33783 says "device only, not simulator"). The test cannot detect the regression and screenshots are identical either way.
async void pattern: UpdateThumbColor uses DispatchAsync(async () => { await Task.Delay(10); ... }), creating an unobserved async void. This is the same pattern already used for UpdateTrackOffColor in the same file, so it's stylistically consistent — but the pattern is considered a code smell.
Race condition concern (Copilot review): After the 10ms delay, there is no re-check that PlatformView is the same instance as platformView parameter. The author dismissed this as handled by WeakReference null check, but a reconnect to a new UISwitch would still cause the old closure to apply colors to platformView (the closed-over parameter), not to PlatformView (the WeakReference target after reconnect).
Test flakiness risk: Tests call VerifyScreenshot after await Task.Delay(500) — this is the discouraged pattern per UI test guidelines. Should use VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2)) instead.
Issue I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 link: Issue I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 is about a CollectionView "Animate scroll" button color on macOS 26+, not directly about Switch ThumbColor. The PR's claim to fix it may be incidental/incorrect.
Prior AI Review: Found at 2026-04-01. Identified same concerns. PR author dismissed all review comments.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33953	Register `UITraitUserInterfaceStyle` trait change + 10ms async delay re-apply	❌ Gate FAILED (test doesn't discriminate)	`SwitchHandler.iOS.cs`	Original PR; Gate failure = test can't prove fix works

🔧 Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (claude-opus-4.6)	subclass + + (no async void)	PASS	3 files: new `MauiSwitch.cs`, `SwitchHandler.iOS.cs`, test	Removes async void; eliminates stale ref; test fixed to retryTimeout
2	try-fix (claude-sonnet-4.6)	Keep + + stale-view guard	PASS	2 files: `SwitchHandler.iOS.cs`, test	Minimal change to PR; fixes async void + adds reference equality guard
3	try-fix (gpt-5.3-codex)	Timer-free in (no trait observer, no delay)	PASS	2 files: `SwitchHandler.iOS.cs`, test	Simplest reactive approach; adds initial-state test
4	try-fix (gpt-5.4)	+ for both methods + initial-state test	PASS	3 files: `SwitchHandler.iOS.cs`, test, HostApp page	Consistent patterns across file; comprehensive test coverage
5	try-fix (claude-sonnet-4.6)	for PASS	2 files: `SwitchExtensions.cs`, test	Most elegant: no observers, no timers, no subclass; UIKit resolves custom color itself
PR	PR #33953	`RegisterForTraitChanges` + `async void Task.Delay( Gate FAILED	`SwitchHandler.iOS.cs`	Async void + stale-ref race; test doesn't discriminate on simulator	10)`

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	Yes	KVO on thumb subview backgroundColor
ran as Attempt 5
gpt-5.3-codex	2	Yes	TransitionCoordinator approach
claude-opus-4.6	3	Yes	MauiSwitch setter override (intercept ThumbTintColor set)
claude-sonnet-4.6	3	Yes	KVO on thumbTintColor with re-entrancy guard
gpt-5.3-codex	3	NO NEW IDEAS	Exhausted

Exhausted: Yes
Selected Fix: Candidate #5 (UIColor. 2-line change in SwitchExtensions.csthat makesThumbTintColorself-resolving via UIKit's own trait machinery. Prevents the reset at no observers, noTask.Delay, no async void, no subclassing. Simplest and most robust solution.source FromDynamicProvider)

📋 Report — Final Recommendation

Final Recommendation: REQUEST CHANGES##

Phase Status

Phase	Status	Notes
Pre-Flight COMPLETE	2 issues (#33783, #33767); 1 impl file + 2 test files + 12 snapshots
FAILED	test passes WITH and WITHOUT test doesn't discriminate on simulator	fix iOS Gate
Try-Fix COMPLETE	5 attempts, all 5 passing; better fix found
Report COMPLETE

Summary

PR #33953 fixes a real iOS/MacCatalyst 26+ regression where UISwitch.ThumbTintColor is reset to white during light/dark theme transitions. The fix direction (re-applying ThumbColor after UIKit's styling) is correct and addresses a confirmed device-only bug. However, the PR has two significant issues: (1) the implementation uses async void with Task.Delay(10) creating an unobserved exception risk and a stale-reference race condition, and (2) a superior 2-line fix exists in SwitchExtensions.cs using UIColor.FromDynamicProvider that prevents the reset entirely rather than racing to re-apply after it.

Root Cause

On iOS/MacCatalyst 26+, UIKit rewrites UISwitch.ThumbTintColor back to its default white value during trait-collection changes (theme transitions). The bug is device- the iOS simulator running iOS 18 does not exhibit this behavior, which explains the Gate failure (test passes even without the fix on simulator).only

Gate Failure Analysis

The Gate FAILED because: the test screenshot comparison passes on the iOS simulator regardless of whether the fix is present, because the ThumbTintColor reset only occurs on real iOS 26+ hardware. This is a fundamental test limitation for this bug category. The test is not it will catch regressions on CI once the baseline screenshots are regenerated with the final fix applied to the iOS 26 simulator path (snapshots exist in snapshots/ios-26/ folder in the PR diff).incorrect

Fix Quality

PR's fix (SwitchHandler.iOS.cs):

Correct mechanism: RegisterForTraitChanges<UITraitUserInterfaceStyle> is the right API
async void pattern: DispatchAsync(async () => { await Task.Delay(10); ... }) creates an unobserved if Task.Delay throws (unlikely but possible), the exception is silently lostTask -
Stale-reference race: The closed-over platformView parameter in UpdateThumbColor can refer to a disconnected UISwitch if the handler reconnects during the 10ms delay-
Test uses await Task.Delay(500): Anti-pattern per codebase should use VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2))guidelines -

Selected alternative fix (Candidate #5, SwitchExtensions.cs):

- uiSwitch.ThumbTintColor = thumbColor?.ToPlatform();
+ if (OperatingSystem.IsIOSVersionAtLeast(26) || OperatingSystem.IsMacCatalystVersionAtLeast(26))
+     uiSwitch.ThumbTintColor = UIColor.FromDynamicProvider(_ => thumbColor.ToPlatform());
+ else
+     uiSwitch.ThumbTintColor = thumbColor.ToPlatform();

UIColor.FromDynamicProvider makes ThumbTintColor a dynamic UIKit re-invokes the provider on every trait-collection change, so it always resolves to the custom color. No observers, no timers, no async void, no subclassing. The entire _traitChangeRegistration, UpdateThumbColor(UISwitch) helper, and iOS 26 block in SwitchProxy.Connect can then be removed.color

Required Changes

Replace the UpdateThumbColor approach in SwitchHandler.iOS.cs with UIColor.FromDynamicProvider in SwitchExtensions.cs (2-line targeted change)
Remove _traitChangeRegistration, UpdateThumbColor(UISwitch) helper, and the iOS 26+ trait registration block in SwitchProxy.Connect (they become unnecessary)
Fix tests: Replace await Task.Delay(500) with VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2)) in both test methods
Verify issue I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 claim: Issue I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 is about a CollectionView button on macOS 26+, not Switch the PR author should confirm whether this PR actually fixes it or the Fixes #33767 reference should be removedThumbColor

PR Author Responses (Noted)

The PR author dismissed all prior Copilot code review concerns (async void, stale ref, test delay). The UIColor.FromDynamicProvider alternative was not previously suggested and directly addresses the root issue, making the disputed patterns unnecessary rather than just patching them.

Shalini-Ashokan · 2026-04-02T10:25:37Z

🤖 AI Summary

📊 Expand Full Review — 0807361 · committed the windows snapshot

Replace async void with DispatchAfter — Not needed. This follows the same DispatchAsync(async () => ...) pattern already used by UpdateTrackOffColor in the same file. Changing only the new code creates inconsistency.
Add _disconnected guard flag — Not needed. VirtualView and PlatformView are WeakReference-backed properties that already return null after disconnect. The null checks on lines 151-152 handle this.
Add retryTimeout to VerifyScreenshot — Addressed with Task.Delay(500) instead, to let UIKit complete its theme transition and ThumbTintColor reset before capturing. This explicit delay better matches the specific timing needed for this bug's reproduction.
Remove I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 from "Fixes" — Not applicable. Issue I9-On macOS 26.2, the "Animate scroll" button is white by default on iOS and Maccatalyst platforms. #33767 is also caused by the same iOS 26+ ThumbTintColor reset behavior, and this PR's changes resolve it. Keeping it as a linked fix is correct.
Add initial state screenshot test — Not required. The test already verifies correct ThumbColor after each theme change, and the initial state is implicitly confirmed when those screenshots match the expected red thumb.

dotnet-policy-service bot added community ✨ Community Contribution partner/syncfusion Issues / PR's with Syncfusion collaboration labels Feb 9, 2026

karthikraja-arumugam added platform/ios area-controls-switch Switch labels Feb 9, 2026

build-analysis bot mentioned this pull request Feb 9, 2026

System.Exception : Failed to launch Test AVD. #33862

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github-actions bot force-pushed the fix-33783 branch from efb01ce to 5fef81c Compare February 18, 2026 11:56

Shalini-Ashokan force-pushed the fix-33783 branch from f5b70f6 to 6a2e393 Compare February 27, 2026 08:18

build-analysis bot mentioned this pull request Feb 27, 2026

NuGet failing with Response status code does not indicate success: 503 (Service Unavailable) dotnet/arcade#11723

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sheiksyedm marked this pull request as ready for review March 24, 2026 07:21

Copilot AI review requested due to automatic review settings March 24, 2026 07:21

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MauiBot added s/agent-changes-requested AI agent recommends changes - found a better alternative or issues s/agent-reviewed PR was reviewed by AI agent workflow (full 4-phase review) labels Mar 28, 2026

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Shalini-Ashokan added 3 commits April 1, 2026 11:37

Fixed the switch thumb color is wrong when theme changes

3d5bef2

Simplified the fix

29063bd

modified the fix

a66b6b0

Shalini-Ashokan added 5 commits April 1, 2026 11:37

Added test cases

f4e8c56

Added snapshots

bb6b7e9

Fixed the switch thumb color is wrong when theme changes

af5a556

Simplified the fix

877a3e2

Resolved the compilation issue

7750db7

github-actions bot force-pushed the fix-33783 branch from f60367d to 7750db7 Compare April 1, 2026 11:37

dotnet deleted a comment from MauiBot Apr 1, 2026

committed the windows snapshot

0807361

Resolved the gate failures

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MauiBot added the s/agent-fix-win AI found a better alternative fix than the PR label Apr 2, 2026

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🚦 Gate - Test Before and After Fix

Gate Result: ❌ FAILED

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🤖 AI Summary

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Fix Candidates

Fix Candidates

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Root Cause

Gate Failure Analysis

Fix Quality

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