Fix UIA Invoke hang when ToolStripMenuItem opens modal dialog from MenuStrip

[LeafShi1]

Fixes #10244

Root Cause

• UI Automation invokes menu items via ToolStripMenuItemAccessibleObject.Invoke, which previously called DoDefaultAction() synchronously.
• When the menu item lives on a MenuStrip and its click handler opens a modal window (e.g. ShowDialog / MessageBox.Show), this happens while WinForms is inside the Win32 “menu mode” message loop.
• The synchronous call starts a nested modal loop inside the menu loop while the UIA client is still blocked waiting for Invoke to return, which can lead to the invoke call appearing “stuck” or the app becoming unresponsive in this scenario.

Proposed changes

• Override ToolStripMenuItemAccessibleObject.Invoke to dispatch the default action asynchronously when the item has an owning ToolStrip with a created handle:
  • If Owner is non-null and Owner.IsHandleCreated is true, call owner.BeginInvoke(new MethodInvoker(DoDefaultAction)); and return immediately.
  • If there is no owner (or no handle yet), fall back to calling DoDefaultAction() directly as before.
• This ensures that for real MenuStrip scenarios the click logic (and any modal UI it shows) runs after the menu loop has exited, under the normal UI message pump, while non-attached/test-only items preserve their existing synchronous behavior.

Customer Impact

• UI Automation tools invoking MenuStrip menu items that open modal dialogs will no longer hang or throw errors, so automated testing and accessibility scenarios can reliably trigger these commands.

Regression?

• Yes

Risk

• Minimal

Screenshots

Before

Accessibility tools and UIA-based automation that invoke ToolStripMenuItem items which open dialogs from a MenuStrip will blocked, invokes will fail to complete.

BeforeChanges.mp4

After

Accessibility tools and UIA-based automation that invoke ToolStripMenuItem items which open dialogs from a MenuStrip will no longer hang or appear blocked, invokes will complete and dialogs will show reliably.

AfterChanges.mp4

Test methodology

• Unit test

Test environment(s)

• .net 11.0.0-preview.2.26080.101

Microsoft Reviewers: Open in CodeFlow

[Shyam-Gupta]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.23985%. Comparing base (9b546b7) to head (43b3a46).
⚠️ Report is 167 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #14301         +/-   ##
===================================================
+ Coverage   77.18395%   77.23985%   +0.05590%     
===================================================
  Files           3279        3279                 
  Lines         645138      645132          -6     
  Branches       47730       47730                 
===================================================
+ Hits          497943      498299        +356     
+ Misses        143503      143126        -377     
- Partials        3692        3707         +15     

Flag	Coverage Δ
Debug	77.23985% <100.00000%> (+0.05590%)	⬆️
integration	19.08742% <0.00000%> (+0.09678%)	⬆️
production	52.16967% <100.00000%> (+0.10648%)	⬆️
test	97.42121% <100.00000%> (+0.01641%)	⬆️
unit	49.55251% <100.00000%> (+0.04988%)	⬆️

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[Copilot]

Pull request overview

This PR addresses a UI Automation (UIA) hang when InvokePattern.Invoke is used on a ToolStripMenuItem hosted by a MenuStrip whose click handler opens modal UI (e.g., ShowDialog). The fix changes the UIA invoke path to dispatch the default action asynchronously when the owning ToolStrip has a created handle, avoiding nested modal/message loops that can make the UIA client appear blocked.

Changes:

• Override ToolStripMenuItemAccessibleObject.Invoke() to BeginInvoke(DoDefaultAction) when the owning ToolStrip handle is created; otherwise fall back to synchronous DoDefaultAction().
• Re-enable and update the previously-skipped unit test scenario that opens a modal dialog from a MenuStrip item.
• Add a new unit test asserting the invoke behavior is asynchronous when the item has an owner with a handle.

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/ToolStripMenuItem.ToolStripMenuItemAccessibleObject.cs	Implements asynchronous UIA invoke dispatch via BeginInvoke when hosted by a handle-created ToolStrip.
src/test/unit/System.Windows.Forms/System/Windows/Forms/AccessibleObjects/ToolStripMenuItem.ToolStripMenuItemAccessibleObjectTests.cs	Updates/regresses the test that previously hung and adds coverage for the new asynchronous behavior.

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