[Windows] Fix WebView Does Not Inherit App Theme by devanathan-vaithiyanathan · Pull Request #35037 · dotnet/maui

devanathan-vaithiyanathan · 2026-04-20T07:35:52Z

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 whether this change resolves your issue. Thank you!

Issue Details

WebView2 on Windows hosts web content in a separate Edge/Chromium browser process that is architecturally decoupled from the WinUI element tree. When MAUI applies an app theme on Windows (e.g., AppTheme.Dark), it sets RequestedTheme on the root FrameworkElement, which propagates to all WinUI controls via normal element tree inheritance.

However, CoreWebView2.Profile.PreferredColorScheme — the browser-level setting that answers web content's prefers-color-scheme CSS media query — is never updated. Its default value is Auto, which reads the OS system theme directly, not the MAUI app theme. So if the user sets AppTheme.Dark in the app while the OS is in light mode, all WinUI controls go dark but the WebView still renders in light mode.

Description of Change

Added PreferredColorScheme logic in UpdateBackground(else part) extension method. It reads WebView2.ActualTheme effective WinUI element theme after inheritance) and maps it to the corresponding CoreWebView2PreferredColorScheme:

ActualTheme	PreferredColorScheme
ElementTheme.Dark	Dark
ElementTheme.Light	Light
Default (follow system)	Auto

Note: This PR includes code changes from PR #34599 My fix is placed in the else block of UpdateBackground, so it needs to be rebased once PR #34599 is merged.

Issues Fixed

Fixes #34823

Tested the behavior in the following platforms.

Android
Windows
iOS
Mac

Before	After
Windows Before.mp4	Windows After.mp4

github-actions · 2026-04-20T07:36:01Z

🚀 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://github.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 35037

Or

Run remotely in PowerShell:

iex "& { $(irm https://github.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 35037"

sheiksyedm · 2026-04-20T11:49:35Z

/azp run maui-pr-uitests, maui-pr-devicetests

azure-pipelines · 2026-04-20T11:49:50Z

Azure Pipelines successfully started running 2 pipeline(s).

Copilot

Pull request overview

This PR targets Windows WebView2 theme integration by mapping MAUI/WinUI effective theme to WebView2’s CoreWebView2.Profile.PreferredColorScheme, so prefers-color-scheme in web content aligns with the app’s theme rather than the OS theme.

Changes:

Add a Windows WebView2 UpdateBackground extension to set DefaultBackgroundColor and adjust PreferredColorScheme.
Wire up IView.Background mapping for Windows WebViewHandler and apply it when CoreWebView2 initializes.
Add a HostApp repro page and an Appium UI test for issue #34823.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/Core/src/Platform/Windows/WebViewExtensions.cs	Implements background + preferred color scheme update logic for WebView2.
src/Core/src/Handlers/WebView/WebViewHandler.cs	Adds Windows mapper entry to update WebView background.
src/Core/src/Handlers/WebView/WebViewHandler.Windows.cs	Adds `MapBackground` and invokes background/theme update on WebView2 initialization.
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34823.cs	Adds UI tests validating WebView appearance under light/dark app themes.
src/Controls/tests/TestCases.HostApp/Issues/Issue34823.cs	Adds HostApp reproduction UI with theme toggle + navigation to a WebView page.

Comments suppressed due to low confidence (1)

src/Core/src/Handlers/WebView/WebViewHandler.Windows.cs:399

PreferredColorScheme is only updated when UpdateBackground is invoked (on CoreWebView2Initialized and when Background changes). If the app theme changes while the WebView is already displayed, nothing re-applies PreferredColorScheme, so the WebView can stay stuck on the previous scheme. Consider subscribing to platformView.ActualThemeChanged (and unsubscribing on disconnect) to call UpdateBackground (or just update PreferredColorScheme) whenever the effective theme changes.

				if (Handler is WebViewHandler handler)
				{
					sender.UpdateUserAgent(handler.VirtualView);
					sender.UpdateBackground(handler.VirtualView);
					if (sender.Source is not null)
					{
						handler.SyncPlatformCookies(sender.Source.ToString()).FireAndForget();
					}

Copilot · 2026-04-20T11:54:55Z

 	[nameof(IView.FlowDirection)] = MapFlowDirection,
+	[nameof(IView.Background)] = MapBackground,


The WINDOWS section of the property mapper is mis-indented compared to the surrounding entries, which makes it easy to miss mappings in reviews/merges. Align the indentation with the other mapper entries inside the initializer.

Suggested change

[nameof(IView.FlowDirection)] = MapFlowDirection,

[nameof(IView.Background)] = MapBackground,

[nameof(IView.FlowDirection)] = MapFlowDirection,

[nameof(IView.Background)] = MapBackground,

Copilot · 2026-04-20T11:54:55Z

+		//TODO: Make it public in .NET 11.
+		internal static void MapBackground(IWebViewHandler handler, IWebView webView)
+		{
+			handler.PlatformView?.UpdateBackground(webView);
+		}


This TODO references ".NET 11" and suggests making MapBackground public, but mapper methods are internal implementation details and the repo is targeting main. Please either remove the TODO or clarify the intended action (e.g., linking to an issue/PR and/or explaining why this needs to be public).

Copilot · 2026-04-20T11:54:55Z

+	[Category(UITestCategories.WebView)]
+	public void WebViewWithDarkTheme()
+	{
+		App.WaitForElement("WebButton");


The test taps "ThemeButton" without first waiting for it to exist. For UI test stability, add a WaitForElement("ThemeButton") before tapping it (especially on slower devices/CI).

Suggested change

App.WaitForElement("WebButton");

App.WaitForElement("WebButton");

App.WaitForElement("ThemeButton");

Copilot · 2026-04-20T11:54:56Z

+			helpPage.NavigatedTo += async (_, __) =>
+			{
+				webView.Source = new HtmlWebViewSource
+				{
+					Html = """
+						<html>
+						<head>
+						  <meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">
+						  <title>Preparing Help</title>
+						  <style>
+						    @media (prefers-color-scheme: dark) {
+						        html, body {
+						            color: white;
+						            background-color: black;
+						        }
+						    }
+
+						    @media (prefers-color-scheme: light) {
+						        html, body {
+						            color: black;
+						            background-color: white;
+						        }
+						    }
+						  </style>
+						</head>
+						<body>
+						<center><h1>Text on a web page</h1></center>
+						</body>
+						</html>
+						"""
+				};
+			};


WebView content is assigned via the NavigatedTo event handler, which introduces timing variability (and the handler is marked async but doesn't await). Consider setting webView.Source before PushAsync (or using a non-async handler) to reduce race/flakiness and remove the unnecessary async event subscription.

Copilot · 2026-04-20T11:54:56Z

+					platformWebView.CoreWebView2.Profile.PreferredColorScheme = CoreWebView2PreferredColorScheme.Light;
+				}
+			}
+			else
+			{
+				if (platformWebView.CoreWebView2 is not null)
+				{
+					platformWebView.CoreWebView2.Profile.PreferredColorScheme = platformWebView.ActualTheme switch
+					{
+						ElementTheme.Dark => CoreWebView2PreferredColorScheme.Dark,
+						ElementTheme.Light => CoreWebView2PreferredColorScheme.Light,
+						_ => CoreWebView2PreferredColorScheme.Auto
+					};
+				}
+			}
+		}
+


When a non-null Background is set, PreferredColorScheme is forced to Light. That can conflict with the app/theme (e.g., if an app sets a dark WebView background for dark mode, web content using prefers-color-scheme will still get Light). Consider deriving PreferredColorScheme from platformWebView.ActualTheme in this branch as well, or basing it on the background color’s luminance if the intent is readability.

Suggested change

platformWebView.CoreWebView2.Profile.PreferredColorScheme = CoreWebView2PreferredColorScheme.Light;

}

}

else

{

if (platformWebView.CoreWebView2 is not null)

{

platformWebView.CoreWebView2.Profile.PreferredColorScheme = platformWebView.ActualTheme switch

{

ElementTheme.Dark => CoreWebView2PreferredColorScheme.Dark,

ElementTheme.Light => CoreWebView2PreferredColorScheme.Light,

_ => CoreWebView2PreferredColorScheme.Auto

};

}

}

}

platformWebView.CoreWebView2.Profile.PreferredColorScheme = GetPreferredColorScheme(platformWebView.ActualTheme);

}

}

else

{

if (platformWebView.CoreWebView2 is not null)

{

platformWebView.CoreWebView2.Profile.PreferredColorScheme = GetPreferredColorScheme(platformWebView.ActualTheme);

}

}

}

static CoreWebView2PreferredColorScheme GetPreferredColorScheme(ElementTheme actualTheme) =>

actualTheme switch

{

ElementTheme.Dark => CoreWebView2PreferredColorScheme.Dark,

ElementTheme.Light => CoreWebView2PreferredColorScheme.Light,

_ => CoreWebView2PreferredColorScheme.Auto

};

kubaflo

Could you please add a snapshot?

devanathan-vaithiyanathan · 2026-04-21T06:40:44Z

Could you please add a snapshot?

@kubaflo , I have added the snapshots for all platform

kubaflo

Could you please review the ai's summary?

…ability (#35133)  > [!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](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you! > **Depends on #35136** (pipeline category detection — should merge first) ## What this does Two things: ### 1. UI test category detection in PR review During the PR review workflow, Step 0.5 detects which UI test categories the PR impacts and writes the result to the AI summary comment. This gives reviewers visibility into which UI tests are relevant. **Detection** reuses the 3-tier script from #35136 (test attributes → source paths → AI reasoning). **AI summary** shows a new 🧪 UI Tests section with detected categories before the gate section. ### 2. Gate reliability fixes Multiple fixes to make the gate (`verify-tests-fail.ps1`) more deterministic: | Fix | Problem it solves | |-----|-------------------| | **Absolute path resolution** | Gate scripts not found on Linux CI agents (`Resolve-Path`, `GetFullPath`) | | **File existence check** | Instant cryptic failure when verify script is missing — now logs clear error | | **3x retry on ENV ERROR** | Emulator timeouts, ADB failures, app crashes — transient issues that pass on retry | | **Strip bad report blocks** | Old verify script produces `Passed: False` with empty counts — stripped instead of shown | | **Gate log in fallback** | When report is missing, shows last 20 lines of gate output instead of just `❌ FAILED / Platform: IOS` | ## Files | File | Changes | |------|---------| | `.github/scripts/Review-PR.ps1` | Step 0.5 category detection + all 5 gate fixes | | `.github/scripts/post-ai-summary-comment.ps1` | Add `uitests` phase to render detected categories | | `.github/pr-review/pr-preflight.md` | Step 7: AI identifies impacted UI test categories | ## Validation — PR reviewer builds (Apr 26) 10 builds against real PRs — all succeeded ✅. Category detection shown in AI summary comment. | PR | Categories Detected | Build | AI Summary | |----|-------------------|-------|------------| | #35037 (WebView theme) | `ViewBaseTests,WebView` | [13940071](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940071) | [comment](#35037 (comment)) | | #35031 (Shell memory leak) | `Shell` | [13940072](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940072) | [comment](#35031 (comment)) | | #35020 (XAML Hot Reload) | _(none — XAML only)_ | [13940073](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940073) | ✅ Shows "No UI test categories" | | #35008 (Shell SearchHandler) | `Shell` | [13940074](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940074) | ✅ | | #34997 (RadioButton gradient) | `RadioButton,ViewBaseTests` | [13940075](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940075) | ✅ | | #34980 (DatePicker rotation) | `ViewBaseTests` | [13940076](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940076) | ✅ | | #34974 (Picker CharacterSpacing) | `ViewBaseTests` | [13940077](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940077) | ✅ | | #34923 (SwipeView threshold) | `SwipeView,ViewBaseTests` | [13940078](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940078) | ✅ | | #34907 (CollectionView ScrollTo) | `CollectionView` | [13940079](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940079) | ✅ | | #34845 (RefreshView binding) | `RefreshView,ViewBaseTests` | [13940080](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=13940080) | ✅ | --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

kubaflo

Could you please resolve conflicts?

MauiBot · 2026-05-03T10:31:55Z

⚠️ Merge Conflict Detected — This PR has merge conflicts with its target branch. Please rebase onto the target branch and resolve the conflicts.

dotnet-policy-service Bot added the partner/syncfusion Issues / PR's with Syncfusion collaboration label Apr 20, 2026

sheiksyedm marked this pull request as ready for review April 20, 2026 11:48

Copilot AI review requested due to automatic review settings April 20, 2026 11:48

sheiksyedm added platform/windows community ✨ Community Contribution area-controls-webview WebView labels Apr 20, 2026

Copilot started reviewing on behalf of sheiksyedm April 20, 2026 11:49 View session

Copilot AI reviewed Apr 20, 2026

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MauiBot added s/agent-changes-requested AI agent recommends changes - found a better alternative or issues s/agent-fix-win AI found a better alternative fix than the PR s/agent-reviewed PR was reviewed by AI agent workflow (full 4-phase review) labels Apr 20, 2026

PureWeen mentioned this pull request Apr 20, 2026

[iOS] Fix StaticResource Hot Reload crash on iOS #35020

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[PR Review Queue] 2026-04-21 #35058

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Integrate UI test category detection into PR review and fix gate reliability #35133

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devanathan-vaithiyanathan added 8 commits May 4, 2026 11:47

fix added

b56ef4f

test added

e63f0d1

changes added

f55d65b

test added

06e96c1

Update Issue34823.cs

2712ef9

test added

c5f5228

Update Issue34823.cs

9647889

snapshot added for all platforms

c88039d

devanathan-vaithiyanathan force-pushed the fix-34823 branch from 294dc1f to c88039d Compare May 4, 2026 06:17

		[nameof(IView.FlowDirection)] = MapFlowDirection,
		[nameof(IView.Background)] = MapBackground,

	App.WaitForElement("WebButton");
	App.WaitForElement("WebButton");
	App.WaitForElement("ThemeButton");

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