Fix issue 14025: [DarkMode] the item lost dot line when using the mouse to expand the dropdown panel for SelectionPanelRadioButton

[SimonZhao888]

Fixes #14025

Root Cause

SelectionPanelRadioButton relies on native painting when used with Appearance.Button, if the focus rectangle is not drawn after native painting completes, it can be missing or inconsistent under certain themes/modes.

Proposed changes

• Override WndProc in SelectionPanelRadioButton and handle WM_PAINT.
• Call base.WndProc(ref m) first to preserve native button visuals.
• Only when Focused && ShowFocusCues, overlay the focus cue by calling ControlPaint.DrawFocusRectangle(...) after WM_PAINT.
• Keep a small inset and bounds validation for the focus rectangle to avoid invalid drawing.

Customer Impact

• [Dark Mode] When using the mouse to expand the dropdown panel for the "Selection Panel" radio button, the dashed line displays correctly

Regression?

• No

Risk

• Mini

Screenshots

Before

After

Dark Mode

14025.mp4

Normal

14025-1.mp4

Test methodology

• Manually

Test environment(s)

• 11.0.0-preview.6.26317

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

Fixes a dark-mode rendering regression in the WinForms designer “Selection Panel” radio-button UI by ensuring the focus cue (dotted rectangle) is drawn consistently after native painting.

Changes:

• Overrides SelectionPanelRadioButton.WndProc to intercept WM_PAINT.
• Calls base.WndProc(ref m) first to preserve native button rendering, then overlays a focus rectangle when Focused and focus cues are shown.
• Adds basic bounds validation/inset to avoid invalid focus-rectangle drawing.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.