fix(win32): Forward Alt+F4 and WM_CLOSE from WebView2 to parent window #22039

Copilot · 2025-12-08T13:22:36Z

GitHub Issue: closes #

PR Type:

🐞 Bugfix

What is the current behavior? 🤔

Pressing Alt+F4 while a WebView2 control has focus closes only the WebView2 itself, leaving the application window open in a broken state with SetWindowRgn errors.

What is the new behavior? 🚀

Alt+F4 and direct WM_CLOSE messages sent to the WebView2 child window are now forwarded to the parent window, closing the entire application as expected.

Implementation:

Added ParentHwnd property (one-line null-coalescing expression) to retrieve parent window handle via XamlRoot
Intercept WM_SYSCOMMAND with SC_CLOSE (Alt+F4) in WebView2's WndProc
Intercept WM_CLOSE messages in WebView2's WndProc
Forward both messages to parent window using SendMessage
Return LRESULT(0) to prevent default child window closure

Constants:

Added WM_SYSCOMMAND and SC_CLOSE to NativeMethods.txt for CsWin32 generation
SC_MASK (0xFFF0) kept as local constant for extracting system command from wParam

PR Checklist ✅

Please check if your PR fulfills the following requirements:

📝 Commits must be following the Conventional Commits specification.
🧪 Added Runtime tests, UI tests, or a manual test sample for the changes have been added (for bug fixes / features) (if applicable)
📚 Docs have been added/updated which fit documentation template (for bug fixes / features)
🖼️ Validated PR Screenshots Compare Test Run results.
❗ Contains NO breaking changes

Other information ℹ️

This fix is specific to Windows/Skia WebView2 implementation. Windows message constants WM_SYSCOMMAND and SC_CLOSE are now defined in NativeMethods.txt and generated by CsWin32 for consistency with the codebase pattern.

Original prompt

This section details on the original issue you should resolve

<issue_title>[Windows/Skia] Alt+F4 on a Focused WebView2 only closes the webview itself</issue_title>
<issue_description>### Current behavior 🐛

When clicking around on the WebView2 everything is looking correct, until you decide to press Alt+F4.

Once pressed, the WebView2 control closes, but the app main window stays.

Interestingly, this breaks the app in an interesting way which resultss in the following errors:
fail: Uno.UI.Runtime.Skia.Win32.Win32NativeElementHostingExtension[0]
      SetWindowRgn failed: The operation completed successfully.

fail: Uno.UI.Runtime.Skia.Win32.Win32NativeElementHostingExtension[0]
      SetWindowRgn failed: The operation completed successfully.

fail: Uno.UI.Runtime.Skia.Win32.Win32NativeElementHostingExtension[0]
      SetWindowRgn failed: The operation completed successfully.

fail: Uno.UI.Runtime.Skia.Win32.Win32NativeElementHostingExtension[0]
      SetWindowRgn failed: The operation completed successfully.
Expected behavior 🎯

Alt+F4 should close the whole window, not just the embedded web view (I think)

How to reproduce it (as minimally and precisely as possible) 🔬

I do this through the Visual Studio IDE extension:

New Project > Uno Application

As minimal setup as possible - Desktop-Only, Skia-based, XAML, MVUX, no DI, no logging...

Once the project is created, edid .csproj - add WebView; at the bottom of the <UnoFeatures>...</UnoFeatures> section

Add WebView2 to the main page ---- <WebView2 Source="https://github.com" />

Start Windows app

Click around in the webview

Press Alt+F4

Workaround 🛠️

Not found, outside of auto unfocusing the WebView2 all the time.

Renderer 🎨

Skia

Native

Affected platforms 📱💻🖥️

Desktop (Windows)

Uno.Sdk version (and other relevant versions) 📦

.NET 10

Uno.Sdk v6.4.40

Microsoft.Web.WebView2 v1.0.3595.46

IDE version 🧑‍💻

Microsoft Visual Studio Community 2026 - 18.0.0 - November 2025 Feature Update

Anything else we need to know? 💬

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes [Windows/Skia] Alt+F4 on a Focused WebView2 only closes the webview itself #22032

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Co-authored-by: MartinZikmund <[email protected]>

CLAassistant · 2025-12-08T13:26:20Z

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ morning4coffe-dev
❌ Copilot
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

Co-authored-by: MartinZikmund <[email protected]>

… SC_CLOSE Co-authored-by: MartinZikmund <[email protected]>

Co-authored-by: MartinZikmund <[email protected]>

unodevops · 2025-12-08T14:12:55Z

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22039/wasm-skia-net9/index.html

unodevops · 2025-12-08T14:43:53Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22039/docs/index.html

jeromelaban · 2025-12-08T15:54:33Z

/azp run

azure-pipelines · 2025-12-08T15:55:02Z

Azure Pipelines successfully started running 2 pipeline(s).

unodevops · 2025-12-08T17:24:46Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22039/docs/index.html

src/Uno.UI.Runtime.Skia.Win32/UI/Xaml/Controls/WebView/Win32NativeWebView.cs

ramezgerges · 2025-12-09T15:00:22Z

src/Uno.UI.Runtime.Skia.Win32/UI/Xaml/Controls/WebView/Win32NativeWebView.cs

+	private const uint WM_SYSCOMMAND = 0x0112;
+	private const uint SC_CLOSE = 0xF060;
+	private const uint SC_MASK = 0xFFF0; // Mask to extract system command from wParam


@copilot Don't define these here. Define what you need in NativeMethods.txt and use it instead. Make sure to keep the alphabetical order in that file.

Done in b0bdb4b. Added WM_SYSCOMMAND and SC_CLOSE to NativeMethods.txt in alphabetical order. SC_MASK is kept as a local constant since it's not a standard Windows API constant but a mask value (0xFFF0) used to extract the system command from wParam.

…pression Co-authored-by: ramezgerges <[email protected]>

…Win32 generation Co-authored-by: ramezgerges <[email protected]>

ramezgerges · 2025-12-09T15:38:03Z

src/Uno.UI.Runtime.Skia.Win32/UI/Xaml/Controls/WebView/Win32NativeWebView.cs

 internal class Win32NativeWebView : INativeWebView, ISupportsVirtualHostMapping
 {
 	private const string WindowClassName = "UnoPlatformWebViewWindow";
+	private const uint SC_MASK = 0xFFF0; // Mask to extract system command from wParam


@copilot why didn't you add this to NativeMethods.txt like the other consts?

SC_MASK (0xFFF0) is not a standard Windows API constant - it's a bit mask value used to extract the system command from wParam. Unlike WM_SYSCOMMAND and SC_CLOSE which are official Windows constants defined in the API, SC_MASK is a utility value. However, if you prefer consistency with the pattern, I can add it to NativeMethods.txt as well. Should I add it?

unodevops · 2025-12-09T15:40:36Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22039/docs/index.html

…tionality

unodevops · 2025-12-14T14:24:51Z

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22039/wasm-skia-net9/index.html

unodevops · 2025-12-14T14:52:10Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22039/docs/index.html

Copilot

Pull request overview

This PR fixes a bug where pressing Alt+F4 on a focused WebView2 control in Windows/Skia would only close the WebView itself instead of the entire application window, leaving the app in a broken state with SetWindowRgn errors.

Key changes:

Added window message forwarding in Win32NativeWebView to intercept Alt+F4 (WM_SYSCOMMAND/SC_CLOSE) and WM_CLOSE messages
Added ParentHwnd property to retrieve the parent window handle for forwarding messages
Created a manual test sample page to verify the fix behavior

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Win32NativeWebView.cs	Added message forwarding logic for WM_SYSCOMMAND and WM_CLOSE to parent window, plus ParentHwnd property
NativeMethods.txt	Added WM_SYSCOMMAND and SC_CLOSE constants for CsWin32 generation
UITests.Shared.projitems	Registered new test page XAML and code-behind files
WebView2_WindowClose.xaml.cs	Implemented manual test page with ViewModel for testing window closing behavior
WebView2_WindowClose.xaml	Created test UI with instructions and checkbox for testing Closing event cancellation

src/Uno.UI.Runtime.Skia.Win32/UI/Xaml/Controls/WebView/Win32NativeWebView.cs

...plesApp/UITests.Shared/Microsoft_UI_Xaml_Controls/WebView2Tests/WebView2_WindowClose.xaml.cs

Co-authored-by: Copilot <[email protected]>

unodevops · 2025-12-17T00:20:16Z

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22039/wasm-skia-net9/index.html

unodevops · 2025-12-17T00:21:15Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22039/docs/index.html

Initial plan

5c5758e

Copilot AI assigned Copilot and MartinZikmund Dec 8, 2025

Copilot started work on behalf of MartinZikmund December 8, 2025 13:23 View session

fix: Forward Alt+F4 and WM_CLOSE from WebView2 to parent window

bebd503

Co-authored-by: MartinZikmund <[email protected]>

Copilot AI and others added 3 commits December 8, 2025 13:33

fix: Use ParentHwnd property to get parent window handle

96b1363

Co-authored-by: MartinZikmund <[email protected]>

fix: Replace magic numbers with named constants for WM_SYSCOMMAND and…

ccf457b

… SC_CLOSE Co-authored-by: MartinZikmund <[email protected]>

fix: Define SC_MASK constant and optimize parentHwnd variable reuse

38953ff

Co-authored-by: MartinZikmund <[email protected]>

Copilot AI changed the title ~~[WIP] Fix Alt+F4 behavior to close main window with WebView2~~ fix(win32): Forward Alt+F4 and WM_CLOSE from WebView2 to parent window Dec 8, 2025

Copilot AI requested a review from MartinZikmund December 8, 2025 13:53

Copilot finished work on behalf of MartinZikmund December 8, 2025 13:53

ramezgerges reviewed Dec 9, 2025

View reviewed changes

src/Uno.UI.Runtime.Skia.Win32/UI/Xaml/Controls/WebView/Win32NativeWebView.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of ramezgerges December 9, 2025 14:58 View session

ramezgerges reviewed Dec 9, 2025

View reviewed changes

refactor: Simplify ParentHwnd property to one-line null-coalescing ex…

b5f123c

…pression Co-authored-by: ramezgerges <[email protected]>

Copilot AI requested a review from ramezgerges December 9, 2025 15:07

Copilot finished work on behalf of ramezgerges December 9, 2025 15:07

Copilot started work on behalf of ramezgerges December 9, 2025 15:07 View session

refactor: Move WM_SYSCOMMAND and SC_CLOSE to NativeMethods.txt for Cs…

b0bdb4b

…Win32 generation Co-authored-by: ramezgerges <[email protected]>

Copilot finished work on behalf of ramezgerges December 9, 2025 15:18

ramezgerges reviewed Dec 9, 2025

View reviewed changes

Copilot started work on behalf of ramezgerges December 9, 2025 15:38 View session

Copilot AI requested a review from ramezgerges December 9, 2025 15:42

Copilot finished work on behalf of ramezgerges December 9, 2025 15:42

feat: Add WebView2 window close test page with keyboard shortcut func…

53d8694

…tionality

github-actions bot added area/automation Categorizes an issue or PR as relevant to project automation kind/documentation labels Dec 14, 2025

morning4coffe-dev mentioned this pull request Dec 14, 2025

fix: macOS window close and quit shortcuts #22134

Draft

5 tasks

morning4coffe-dev marked this pull request as ready for review December 16, 2025 15:38

Copilot AI review requested due to automatic review settings December 16, 2025 15:38

Copilot AI reviewed Dec 16, 2025

View reviewed changes

chore: Apply suggestions from code review

af41799

Co-authored-by: Copilot <[email protected]>

fix(win32): Forward Alt+F4 and WM_CLOSE from WebView2 to parent window #22039

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fix(win32): Forward Alt+F4 and WM_CLOSE from WebView2 to parent window #22039

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PR Type:

What is the current behavior? 🤔

What is the new behavior? 🚀

PR Checklist ✅

Other information ℹ️

Expected behavior 🎯

How to reproduce it (as minimally and precisely as possible) 🔬

Workaround 🛠️

Renderer 🎨

Affected platforms 📱💻🖥️

Uno.Sdk version (and other relevant versions) 📦

IDE version 🧑‍💻

Anything else we need to know? 💬

Comments on the Issue (you are @copilot in this section)

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