Fix issue 14094: After reducing the form width, clicking the ToolStrip options triggers a Win32Exception error

[SimonZhao888]

Fixes #14094

Proposed changes

• Ensure hosted controls are only reparented to ToolStrip parents after the parent handle is created, preventing SetParent failures when items overflow.
• Added a regression test to verify ToolStripControlHost controls with existing handles can move into the overflow drop-down without throwing.

Customer Impact

• When the form width is reduced to prevent Toolstrip items from displaying, clicking the ToolBar Options no error throws and Toolstrip items show correctly.

Regression?

• Yes

Risk

-Min

Screenshots

Before

After

Bug14094.mp4

Test methodology

• Manually

Test environment(s)

• 11.0.0-alpha.1.25619.109

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

Fixes Win32Exception when ToolStripControlHost-hosted controls (e.g., ToolStripComboBox/ToolStripProgressBar) move into the overflow drop-down after the form is narrowed, by ensuring the ToolStrip parent has a handle before reparenting hosted controls.

Changes:

• Update ToolStripControlHost.SyncControlParent() to create the ToolStrip parent handle when the hosted control handle already exists.
• Add a regression test covering moving hosted controls with existing handles into the overflow drop-down without throwing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripControlHost.cs	Ensures the ToolStrip parent handle exists before adding the hosted control to the ToolStrip’s control collection.
src/test/unit/System.Windows.Forms/System/Windows/Forms/ToolStripControlHostTests.cs	Adds a regression test intended to reproduce/guard against the overflow reparenting Win32Exception scenario.

[LeafShi1]

LGTM! The failed tests need to be addressed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.17980%. Comparing base (86f2d9a) to head (1d3fba0).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #14244         +/-   ##
===================================================
+ Coverage   77.17712%   77.17980%   +0.00267%     
===================================================
  Files           3279        3279                 
  Lines         645129      645161         +32     
  Branches       47728       47730          +2     
===================================================
+ Hits          497892      497934         +42     
+ Misses        143544      143528         -16     
- Partials        3693        3699          +6     

Flag	Coverage Δ
Debug	77.17980% <100.00000%> (+0.00267%)	⬆️
integration	18.98827% <55.55556%> (-0.00054%)	⬇️
production	52.05190% <100.00000%> (+0.00481%)	⬆️
test	97.40497% <100.00000%> (+0.00018%)	⬆️
unit	49.51635% <100.00000%> (+0.02956%)	⬆️

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