fix issues#12941 Combox autocomplete list weird selection behaviour

[Epica3055]

Fixes #12941

Proposed changes

• when OnKeyDown is triggered, Hide dropdown properly.

Regression?

• No

Screenshots

Before

WinFormsApp-TestCombobox_eC5825XdQA.mp4

After

Issue_12941.mp4

Test methodology

• Manual

Microsoft Reviewers: Open in CodeFlow

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

src/System.Windows.Forms/src/System/Windows/Forms/Controls/ComboBox/ComboBox.cs:2438

• [nitpick] The comment 'for fix' should be more descriptive, such as 'Fix for issue Combox autocomplete list weird selection behaviour #12941: Hide dropdown when a non-control key is pressed in AutoComplete mode'.

// for fix https://github.com/dotnet/winforms/issues/12941

src/System.Windows.Forms/src/System/Windows/Forms/Controls/ComboBox/ComboBox.cs:2439

• Ensure that the new behavior of hiding the dropdown when a non-control key is pressed in AutoComplete mode is covered by tests.

char input = (char)e.KeyValue;

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 76.01253%. Comparing base (ff19802) to head (6752039).
Report is 79 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #12999         +/-   ##
===================================================
- Coverage   76.13911%   76.01253%   -0.12659%     
===================================================
  Files           3258        3267          +9     
  Lines         642851      643465        +614     
  Branches       47307       47433        +126     
===================================================
- Hits          489461      489114        -347     
- Misses        149825      150790        +965     
+ Partials        3565        3561          -4     

Flag	Coverage Δ
Debug	76.01253% <33.33333%> (-0.12659%)	⬇️
integration	18.02927% <0.00000%> (-0.14390%)	⬇️
production	49.96040% <33.33333%> (-0.12258%)	⬇️
test	96.93683% <ø> (-0.03306%)	⬇️
unit	47.41202% <33.33333%> (-0.01555%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[LeafShi1]

LGTM！

[ricardobossan]

All LGTM!

[Tanya-Solyanik]

This change in behavior might not work for some users. For example, if the autocomplete list is not displayed because what the user types is not in the drop-down list, we shouldn't close the drop down. I would rather not fix it.

[merriemcgaw]

I'm going to have to agree here. I don't like that change in behavior.