Fix issue 15031: Disable NET11 VisualStylesMode for composite controls (ToolStrip, DataGridView, etc.) until NET11 layout modernization is completed

[SimonZhao888]

Fixes #15031

Proposed changes

• Fall back to Classic rendering for ToolStrip, MenuStrip, and DataGridView when Net11 visual styles are requested.
• Add AppContext switches to opt these controls into Net11 rendering:

• System.Windows.Forms.ToolStripModernRendering
• System.Windows.Forms.DataGridViewModernRendering

• Preserve visual-style inheritance and change-notification behavior for coerced modes.

Customer Impact

• ToolStrip, MenuStrip, and DataGridView use stable Classic rendering by default until their Net11 layout modernization is complete.
• Applications can opt into Net11 rendering through the corresponding AppContext switches.
• Existing applications retain their current behavior unless explicitly opted in.

Regression?

• No

Risk

• Mini

Screenshots

Before

After

Screen.Recording.2026-09-08.164528.mp4

Screen.Recording.2026-09-08.164230.mp4

Test methodology

• Manually
• Automated test cases

Accessibility testing

Test environment(s)

• 11.0.0-preview.7.26381.103

Microsoft Reviewers: Open in CodeFlow

[Copilot]

🟡 Changes recommended

The current OnParentVisualStylesModeChanged early-return path can suppress propagation/notifications when removing a local VisualStylesMode value changes the effective mode under coercion.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Disables modern VisualStylesMode rendering for composite controls (currently ToolStrip and DataGridView) by coercing Net11/Latest requests to Classic, and adds unit tests to lock in the expected effective-mode behavior and eventing.

Changes:

• Add per-control coercion hook (GetSupportedVisualStylesMode) and override it in ToolStrip/DataGridView to force Classic for Net11 and newer modes.
• Adjust Control visual-styles inheritance / transition plumbing to account for coercion when determining effective-mode changes.
• Add unit tests validating ToolStrip/DataGridView effective mode is Classic under modern requests and that parent modern-mode transitions do not raise VisualStylesModeChanged when effective mode is unchanged.

File summaries

File	Description
src/System.Windows.Forms/System/Windows/Forms/Control.cs	Adds supported-mode coercion hook and updates inheritance/transition logic to respect coerced effective modes.
src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs	Forces Net11/Latest requests to use Classic effective visual styles mode.
src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridView.cs	Forces Net11/Latest requests to use Classic effective visual styles mode.
src/test/unit/System.Windows.Forms/System/Windows/Forms/ToolStripTests.cs	Adds tests ensuring modern requests result in Classic effective mode and no spurious change events.
src/test/unit/System.Windows.Forms/System/Windows/Forms/DataGridViewTests.cs	Adds tests ensuring modern requests result in Classic effective mode and no spurious change events.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.24166%. Comparing base (f0cd8e4) to head (f93a065).

Additional details and impacted files

@@              Coverage Diff              @@
##                main      #15033   +/-   ##
=============================================
  Coverage   37.24166%   37.24166%           
=============================================
  Files            246         246           
  Lines           9774        9774           
  Branches        1029        1029           
=============================================
  Hits            3640        3640           
  Misses          5970        5970           
  Partials         164         164           

Flag	Coverage Δ
Debug	37.24166% <ø> (ø)
production	39.36526% <ø> (ø)
test	20.64923% <ø> (ø)
unit	39.36526% <ø> (ø)

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[KlausLoeffelmann]

@LeafShi1, @SimonZhao888, @ricardobossan ... and also everybody else - just asking:

Should we quirk that with an AppContext switch?
(And I am NOT saying we should. But I am also not saying we should not.)

[KlausLoeffelmann]

Yes!!
Can't wait to see this live!!

Thanks a lot!

[SimonZhao888]

Yes!! Can't wait to see this live!!

Thanks a lot!

Did you misread that PR draft? It likely still needs further revision.