[MessageBar] Fix NullReferenceException and thread safety in MessageService#4677
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JamesNK wants to merge 3 commits intomicrosoft:mainfrom
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[MessageBar] Fix NullReferenceException and thread safety in MessageService#4677JamesNK wants to merge 3 commits intomicrosoft:mainfrom
JamesNK wants to merge 3 commits intomicrosoft:mainfrom
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- Add null check on OnMessageItemsUpdatedAsync before invoking in ShowMessageBarAsync, using local variable capture for thread safety. - Return snapshot copies from AllMessages and MessagesToShow instead of the live MessageList reference to prevent concurrent modification errors. Fixes microsoft#4674
vnbaaij
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Apr 7, 2026
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Hi @JamesNK please re-target this PR to go to the dev branch |
dvoituron
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Apr 7, 2026
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As Vincent pointed out, the PR should be merged into dev, not main
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Rolled up into #4680. Thanks again for your contribution! |
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Summary
Fix #4674
NullReferenceException in
ShowMessageBarAsyncShowMessageBarAsynccalledawait OnMessageItemsUpdatedAsync!.Invoke()without a null check. IfShowMessageBarAsyncis called beforeFluentMessageBarProvider.OnInitializedsubscribes to the event, this throws aNullReferenceException. The delegate is now captured in a local variable before invoking for thread safety:Thread safety of
AllMessagesandMessagesToShowBoth properties/methods acquired a read lock but returned the live
MessageListreference. The lock was released before the caller could enumerate, so concurrent writes (e.g. adding a message) could modify the collection during enumeration, causingInvalidOperationException.Both now return a snapshot copy via
.ToList()while still holding the read lock.