Reset MouseIsOver when the control loses focus

[LeafShi1]

Fixes #12590

Root Cause

In order to fix the flickering issue#2053861, we modified the drawing logic of ComboBox in #11529

When FlatStyle == FlatStyle.Popup and the control gets the focus or the mouse entering, draw the black border of the popup instead of re-rendering the entire control

This leads to the current issue. When the drop-down box is expanded by the mouse, and the focus is moved to the property page using Tab, FlatStyle is changed to popup, and then the RightToLeft property is modified

At this time, the conditions for drawing the Popup border are met (i.e. FlatStyle == FlatStyle.Popup and MouseIsOver=true), which causes DrawFlatCombo not to be executed

Proposed changes

• Set MouseIsOver = false in OnLostFocus method of ComboBox.cs

Customer Impact

• ComboBox dropdown button can be shown normally when switching RightToLeft property, or recreating the combobox for any other reason.

Regression?

• Yes

Risk

• Minimal

Screenshots

Before

When change the RightToLeft property after expanding the Popup FlatStyle comboBox, the dropdown button on the comboBox disappeared

After

The dropdown button on the comboBox can be show normally

Test methodology

• Manually

Test environment(s)

• .net 10.0.0-alpha.1.24605.1

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 86.20690% with 4 lines in your changes missing coverage. Please review.

Project coverage is 76.03698%. Comparing base (af49f16) to head (75ca31f).
Report is 117 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #12598         +/-   ##
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+ Coverage   75.73242%   76.03698%   +0.30455%     
===================================================
  Files           3153        3164         +11     
  Lines         635807      639335       +3528     
  Branches       46975       47188        +213     
===================================================
+ Hits          481512      486131       +4619     
+ Misses        150870      149697       -1173     
- Partials        3425        3507         +82     

Flag	Coverage Δ
Debug	76.03698% <86.20690%> (+0.30455%)	⬆️
integration	18.15167% <0.00000%> (-0.10286%)	⬇️
production	49.79835% <20.00000%> (+0.49282%)	⬆️
test	97.02935% <100.00000%> (-0.02059%)	⬇️
unit	47.02069% <20.00000%> (+0.75762%)	⬆️

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[ricardobossan]

I proceeded to test this PR and the issue has been resolved:

All LGTM!

[LeafShi1]

The first repair idea is changing MouseIsOver to False when the control loses focus, but there is a problem here that the mouse is actually still in the hovering state when the control loses focus, as shown in the figure below. When the focus is switched using Tab, the mouse hovering position remains unchanged. At this time, MouseIsOver=false will cause DrawFlatCombo to be executed and the Popup's black border will disappear.

Therefore, when changing the property value while the mouse is hovering, the control must be drawn in its basic form before drawing the black border of the Popup. So I redrawn the DropDown button when executing DrawPopUpCombo in the latest commit

This inevitably causes the DropDown button to flicker when the cursor moves between the DropDown button and the edit box

@Tanya-Solyanik Do you have other suggestions?