fix: detach platform input when presentation source closes - #21782
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MrJul merged 4 commits intoJul 21, 2026
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Closed top levels retain the presentation source as the platform input callback. A late platform input event can therefore target an already disposed visual tree.\n\nThe regression test requires top-level closure to clear ITopLevelImpl.Input.
Win32 can deliver WM_CAPTURECHANGED while destroying a popup that owns mouse capture. The platform then calls the input handler retained by the disposed presentation source, which logs a warning and can route input into a detached visual tree.\n\nClear the platform input callback at the start of presentation source disposal, alongside the existing scaling event unsubscription.
NathanDrake2406
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July 15, 2026 08:03
MrJul
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MrJul
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* test: cover platform input detachment on close Closed top levels retain the presentation source as the platform input callback. A late platform input event can therefore target an already disposed visual tree.\n\nThe regression test requires top-level closure to clear ITopLevelImpl.Input. * fix: detach platform input when presentation source closes Win32 can deliver WM_CAPTURECHANGED while destroying a popup that owns mouse capture. The platform then calls the input handler retained by the disposed presentation source, which logs a warning and can route input into a detached visual tree.\n\nClear the platform input callback at the start of presentation source disposal, alongside the existing scaling event unsubscription. --------- Co-authored-by: Julien Lebosquain <julien@lebosquain.net>
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What does the pull request do?
Detaches the platform input callback when a presentation source closes. This prevents late native input, including Win32
WM_CAPTURECHANGED, from reaching an already disposed popup or window.What is the current behavior?
The Win32 handling added by #19685 forwards
WM_CAPTURECHANGEDthroughITopLevelImpl.Input. When a menu item closes a native popup while that popup owns mouse capture, Win32 can destroy the popup and then send the capture-loss message.PresentationSource.Disposeclears itsPlatformImplreference but leavesITopLevelImpl.Inputassigned toPresentationSource.HandleInput. The late message therefore enters the disposed presentation source, logsPlatformImpl is null, couldn't handle input, and can route later input work toward a detached visual tree.What is the updated/expected behavior with this PR?
Closing a top level clears
ITopLevelImpl.Inputbefore layout and renderer teardown, so the native implementation cannot dispatch input after close handling starts.Validation:
Closing_Should_Detach_Platform_Input_Handler, which fails before the fix because the closed top level retains the callback.Avalonia.Controls.UnitTestsexecutable: 3,643 passed, 1 existing test skipped, 0 failed.How was the solution implemented (if it's not obvious)?
PresentationSourceassigns and owns the platform input callback. Disposal now clears it alongsideScalingChangedbefore layout and renderer teardown.The change does not alter pointer capture, popup close ordering, or public API. The regression test verifies the framework/platform ownership boundary using the mock top-level implementation. Native Win32 UI automation was not run because the development host is macOS.
Checklist
Breaking changes
None.
Obsoletions / Deprecations
None.
Fixed issues
Fixes #19892