Avoid exceptions when getting a position from a PointerEventArgs#21301
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MrJul merged 1 commit intoMay 4, 2026
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Return null when an IPresentationSource can't convert from/to screen coordinates Document exceptions in VisualExtensions PointToClient and PointToScreen Add tests for cross-root pointer event positions
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MrJul
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May 28, 2026
…niaUI#21301) Return null when an IPresentationSource can't convert from/to screen coordinates Document exceptions in VisualExtensions PointToClient and PointToScreen Add tests for cross-root pointer event positions
MrJul
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#21294 identifies a case in which
PointerEventArgs.GetPositioncan throw. The bug report blamesItemSelectionEventTriggers.IsPointerEventWithinBounds, which is where the exception was observed. But the problem is more general than that.What is the current behaviour?
Inspecting the code of
GetPosition, it's clear that the intent is to return (0,0) if a position can't be calculated. However, it will in fact throw if_rootVisual.VisualRootis null when the method is called.What is the updated/expected behavior with this PR?
GetPositionis no longer dependent on the value of_rootVisual.VisualRoot, and so no longer throws if it's null.VisualExtensions.PointToClientandPointToScreenare now documented.How was the solution implemented (if it's not obvious)?
I refactored
PointerEventArgs.GetPositionto use the newIPresentationSource.PointToClientandPointToScreenmethods when transforming a point between two presentation sources. We can bypass theVisualExtensionsequivalents because we already know that the position is in the coordinate space of the presentation source which raised the event.This refactoring allows us to store
rootVisual.PresentationSourcein the constructor instead ofrootVisualitself. This protects us from the property changing later. The onlyVisualinvolved is now the one passed toGetPosition.IPresentationSource.PointToClientandPointToScreennow returnnullif they failed to transform the point, so that callers can respond appropriately.Breaking changes
None.
Obsoletions / Deprecations
None.
Fixed issues
Fixes #21294