Use MouseWheel scrolling in ToolStripDropDownMenu

[toehead2001]

Fixes #13302

Proposed changes

• Add an OnMouseWheel override on ToolStripDropDownMenu to handle scrolling the menu items.

Customer Impact

• Allow users to scroll a ToolStripDropDownMenu with the Mouse Wheel.

Regression?

• No

Risk

• Could potentially cause an issue if an application already has an override/event for handling MouseWheel on an ToolStripDropDownMenu.
• Maybe need to add a property to make this opt-in or opt-out.

Test methodology

• Manually tested through the user interface of scratch project.

Microsoft Reviewers: Open in CodeFlow

[Tanya-Solyanik]

Error:
src\System.Windows.Forms\System\Windows\Forms\Controls\ToolStrips\ToolStripDropDownMenu.cs#L847

src\System.Windows.Forms\System\Windows\Forms\Controls\ToolStrips\ToolStripDropDownMenu.cs(847,29): error RS0016: (NETCORE_ENGINEERING_TELEMETRY=Build)
Symbol 'override System.Windows.Forms.ToolStripDropDownMenu.OnMouseWheel(System.Windows.Forms.MouseEventArgs! e) -> void'
is not part of the declared public API (https://github.com/dotnet/roslyn-analyzers/blob/main/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.89944%. Comparing base (7c04597) to head (be95b05).
⚠️ Report is 249 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13303         +/-   ##
===================================================
- Coverage   76.90689%   76.89944%   -0.00746%     
===================================================
  Files           3260        3260                 
  Lines         643088      643110         +22     
  Branches       47601       47605          +4     
===================================================
- Hits          494579      494548         -31     
- Misses        144845      144893         +48     
- Partials        3664        3669          +5     

Flag	Coverage Δ
Debug	76.89944% <0.00000%> (-0.00746%)	⬇️
integration	18.97564% <0.00000%> (-0.01227%)	⬇️
production	51.56089% <0.00000%> (-0.01472%)	⬇️
test	97.42152% <ø> (ø)
unit	48.95130% <0.00000%> (-0.00826%)	⬇️

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[Copilot]

Pull Request Overview

This PR adds support for scrolling a ToolStripDropDownMenu using the mouse wheel, addressing issue #13302.

• Implements an override of OnMouseWheel in ToolStripDropDownMenu to calculate and apply a scroll amount.
• Updates PublicAPI.Unshipped.txt to document the new override.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripDropDownMenu.cs	Added OnMouseWheel override handling scroll logic.
src/System.Windows.Forms/PublicAPI.Unshipped.txt	Added API declaration for the new override.

Comments suppressed due to low confidence (1)

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripDropDownMenu.cs:865

• [nitpick] Consider renaming 'delta' to 'scrollDelta' to clarify that it represents the scroll amount calculated from the mouse wheel event.

int delta = firstItemBounds.Height * SystemInformation.MouseWheelScrollLines * -Math.Sign(e.Delta);

[Tanya-Solyanik]

System.Windows.Forms.Tests.ClipboardTests.SetDataObject_InvokeObjectBoolNotIComDataObject_GetReturnsExpected(data: "data", copy: True)

Error message
Expected object to be "data", but found "".

Stack trace
at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
at FluentAssertions.Execution.AssertionChain.FailWith(Func1 getFailureReason) at FluentAssertions.Primitives.ObjectAssertions2.Be(TSubject expected, String because, Object[] becauseArgs)
at System.Windows.Forms.Tests.ClipboardTests.SetDataObject_InvokeObjectBoolNotIComDataObject_GetReturnsExpected(Object data, Boolean copy) in /_/src/test/unit/System.Windows.Forms/System/Windows/Forms/ClipboardTests.cs:line 307
at InvokeStub_ClipboardTests.SetDataObject_InvokeObjectBoolNotIComDataObject_GetReturnsExpected(Object, Span`1)
at System.Reflection.MethodBaseInvoker.InvokeWithFewArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

[toehead2001]

That error looks unrelated to the code changes in this PR.

[Tanya-Solyanik]

That error looks unrelated to the code changes in this PR.

@toehead2001 - I'm adding these errors for our internal tracking. ClipboardTests is a known flaky set of tests because they read from a machine-wide resource, we ignore any non-recurring failures there.

[Tanya-Solyanik]

Could you please explain why the base class handling in insufficient?

[toehead2001]

The direct base class (ToolStripDropDown) doesn't have a implementation of OnMouseWheel, so what gets called here is the implementation all the way down in ScrollableControl.
Obviously, ScrollableControl doesn't know how to handle the re-positioning of ToolStripItems, and just handles normal Controls.

[Tanya-Solyanik]

Right, but why does scrollable control need to know about the ToolStripItems. Is ClientRectangle or Display rectangle calculated incorrectly in this case?

[toehead2001]

The parent ToolStrip class has it own scroll implementation that doesn't use OnScroll() of ScrollableControl.

winforms/src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs

Line 4051 in 7c04597

internal virtual void ScrollInternal(int delta)

I am not sure why it was originally designed that way.