Fix nth-child styles on virtualized lists
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The `IValueEntry.HasValue` and `ValueFrame.IsActive` properties could alter state, which meant that when inspecting objects with these properties in a debugger, the state got altered by observing it. Make them methods.
Break the rules in this case. Fixes #12381
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* Don't alter state in properties. The `IValueEntry.HasValue` and `ValueFrame.IsActive` properties could alter state, which meant that when inspecting objects with these properties in a debugger, the state got altered by observing it. Make them methods. * Deleted unused file. * Add failing test for #12381. * Use the index from the event in EvaluateIsActive. Break the rules in this case. Fixes #12381 --------- Co-authored-by: Max Katz <maxkatz6@outlook.com>
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What does the pull request do?
#12381 occurs when there are multiple
nth-childstyles applied to a virtualized list.The fix is to always use the index from the
ChildIndexChangedEventArgsevent inNthChildActivator.EvaluateIsActive.The docs for
StyleActivatorBase.EvaluateIsActivesay:Which is good advice in general, however in this case we need to break the rule and use the value from the event subscription where possible instead of calling
IChildIndexProvider.GetChildIndex. This is because this event can be fired during the process of realizing an element of a virtualized list; in this case there may be more than onenth-childstyle on a the list item and when the other is re-evaluated, callingGetChildIndexmay not return the correct index as the element isn't yet realized."Bonus" fix
The
IValueEntry.HasValueandValueFrame.IsActiveproperties could alter state, which meant that when inspecting objects with these properties in a debugger, the state got altered by observing it. Make them methods, which makes debugging stuff like this a lot less frustrating! (Most of this PR is actually this change, the meat of the actual fix for #12381 is inNthChildActivator.)Fixed issues
Fixes #12381