[release/9.0] Fix #12661 Null Reference Exception: System.Windows.Forms.TabControl.<WmSelChange> #12728
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…utomationEventRaised() test
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## release/9.0 #12728 +/- ##
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+ Coverage 74.82960% 97.00847% +22.17887%
======================================================
Files 3022 1066 -1956
Lines 630276 345877 -284399
Branches 46797 5040 -41757
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- Hits 471633 335530 -136103
+ Misses 155260 9625 -145635
+ Partials 3383 722 -2661
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Backport of #12683 to release/9.0
Fixes #12661
/cc @LeafShi1 @John-Qiao
Customer Impact
A customer reported a crash in their application that uses WinForms TabControl and requested a fix in NET8 release. Application is running under accessibility tools and is removing TabPages from a control dynamically. When the selected page is removed, the selection moves to the next page and the corresponding accessibility event is queued using BeginInvoke to be raised. If by the time the event is raised, the page is removed, a NullReferenceException is thrown. No workaround is available.
Fix
Test if the selected page is still available before raising the accessibility event inside the BeginInvoke delegate.
Testing
Manual with the customer repro case and unit tests.
Risk
Low - this is an additional validation only.
Microsoft Reviewers: Open in CodeFlow