Avoid NullReferenceException in Gestures.PointerReleased #15117
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* refs #14249 Avoid NullReferenceException in Gestures.PointerReleased * refs #14249 Track current gesture state with single readonly struct * Update from review * Moved the last click location from the GestureState record to a separate field. (#14249) --------- Co-authored-by: Заболотнев Юрий <zabolotnev@promit-ek.ru>
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What does the pull request do?
PR allows you to avoid crashes during multi-touch input #14249. This is not a complete fix as I'm not sure the new behavior is correct.
What is the current behavior?
The bug is described in #14249. In my case, I created an application with one large button. I pressed the Linux device's touch display several times with three fingers. After a few touches the app crashes with message:
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at Avalonia.Input.Gestures.PointerReleased(RoutedEventArgs ev)
What is the updated/expected behavior with this PR?
The application does not crash.
How was the solution implemented (if it's not obvious)?
There is three ways to avoid NRE here:
PointerReleasedbefore raising the event. In this case theHoldingState.Completedevent will not be raised in some cases. Is it good or bad? I don't know.s_lastHeldPointer.Typein separate field. EventHoldingState.Completedwill be raised even ifs_lastHeldPointerisnull. I think this is better than the first case.s_lastHeldPointermight benulland causes NRE and rewrite (refactor?) this code.I decided to take the second path as it is more reliable. I also changed the
PointerPressedandPointerMovedmethods to uses_lastHeldPointerTypefield just for consistency. These two methods do not throw NRE exceptions.Checklist
Breaking changes
Obsoletions / Deprecations
Fixed issues