[Epic] .NET 11 new WinForms API surface (accessibility-driven)

[KlausLoeffelmann]

Overview

Tracking issue for the .NET 11 WinForms API proposals authored/updated in this batch. Each is its own api-suggestion issue and stands on its own for API review; this issue exists to keep them visible as a related cluster and to track implementation status and cross-cutting follow-up work.

API proposals in this batch

• [NET 11 API Proposal] Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting #14583 - Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting (branch Net11Api_01_New_Application_Api also adds Application.GetWindowsAccentColor())
• [NET11 API Proposal] TreeView.NodeLeading - opt-in honest, text-scale-aware node-row height #14584 - TreeView.NodeLeading - opt-in, text-scale-aware node-row height (depends on [NET 11 API Proposal] Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting #14583)
• [.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585 - Add APIs for performance improved, flicker-free WinForms UI mutation (ISupportSuspendPainting/ISupportSuspendRelocation, Form.FormRevealMode)
• [.NET 11 API Proposal] Introduce KioskModeManager component #14586 - Introduce KioskModeManager component
• [NET11 new API] Visual Styles feature (postponed from .NET 9 and .NET 10) #14587 - Visual Styles feature (VisualStylesMode), postponed from .NET 9 and .NET 10

Related, not part of this batch:

• Introduce ApplicationDefaults for Application and the Application Framework #4958 - Introduce ApplicationDefaults for Application and the VB Application Framework (the existing ApplyApplicationDefaults mechanism these proposals extend)
• [API Suggestion] Introduce Modern Visual Styles for Apps targeting .NET 11+ and Win 11+ for A11Y improvements. (Was DarkMode/VisualStyles) #7641 - Original upstream dark-mode/Visual Styles ask that [NET11 new API] Visual Styles feature (postponed from .NET 9 and .NET 10) #14587 was extracted from
• [API Proposal] DeferLocationChange - batch child-control location changes (split from #14585, postponed) KlausLoeffelmann/winforms#12 - DeferLocationChange batch child-location API, split out of [.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585 and postponed

Implementation tracking

Each feature branch is tracked with three independent check-offs:

1. Branch Implemented - the branch matches the current, agreed API shape in the linked issue and builds/tests cleanly.
2. Klaus Test-App Approval - exercised through the shared exploratory test app and Klaus is satisfied with the runtime behavior.
3. WinForms Team Testing - Olina or Leaf (Beyondsoft) have tested and signed off.

#14585 - Flicker-free UI mutation (ISupportSuspendPainting/ISupportSuspendRelocation, Form.FormRevealMode)

Branch: KlausLoeffelmann/winforms @ Net11Api_03_ImproveControlRendering (renamed from ImproveControlPositioningAndRendering now that DeferLocationChange is split out)

• Branch Implemented
• Klaus Test-App Approval
• WinForms Team Testing

#14587 - Visual Styles (VisualStylesMode, modern Button/CheckBox/RadioButton, TextBoxBase.Padding)

Branch: KlausLoeffelmann/winforms @ Net11Api_05_VisualStylesMode

• Branch Implemented
• Klaus Test-App Approval
• WinForms Team Testing

#14586 - KioskModeManager component

Branch: KlausLoeffelmann/winforms @ Net11Api_04_KioskManagerComponent

• Branch Implemented
• Klaus Test-App Approval
• WinForms Team Testing

#14583 - Application.SystemTextSize / SystemTextSizeAwareness

Branch: KlausLoeffelmann/winforms @ Net11Api_01_New_Application_Api

• Branch Implemented
• Klaus Test-App Approval
• WinForms Team Testing

#14584 - TreeView.NodeLeading

Branch: KlausLoeffelmann/winforms @ Net11Api_02_TreeView_NodeLeading

• Branch Implemented
• Klaus Test-App Approval
• WinForms Team Testing

Refactoring / follow-up work tracked here

• Rework [.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585: rename FormAppearanceMode -> FormRevealMode (Inherit/Classic/Deferred); remove the DeferLocationChange sub-feature (now tracked separately, see [API Proposal] DeferLocationChange - batch child-control location changes (split from #14585, postponed) KlausLoeffelmann/winforms#12); change SuspendPaintingScope/SuspendRelocationScope from readonly ref struct to sealed class : IDisposable; make ISupportSuspendPainting/ISupportSuspendRelocation explicit interface implementations on Control with protected ...Core() hooks instead of public virtual methods; add Application.DefaultFormRevealMode / SetDefaultFormRevealMode / IsFormRevealDeferred. (Issue text updated; branch implementation tracked above.)
• Extend [NET11 new API] Visual Styles feature (postponed from .NET 9 and .NET 10) #14587's API Proposal with Microsoft.VisualBasic.ApplicationServices.ApplyApplicationDefaultsEventArgs.VisualStylesMode, completing the VB Application Framework wiring anticipated (but never finished) back in the .NET 9 Visual Styles attempt. (Issue text updated; branch implementation tracked above.)
• Extend [.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585's API Proposal with Microsoft.VisualBasic.ApplicationServices.ApplyApplicationDefaultsEventArgs.FormRevealMode, following the same ColorMode/HighDpiMode pattern already established in that class. (Issue text updated; branch implementation tracked above.)
• Normalize Markdown paragraph formatting across [NET 11 API Proposal] Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting #14583, [NET11 API Proposal] TreeView.NodeLeading - opt-in honest, text-scale-aware node-row height #14584, [.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585, [.NET 11 API Proposal] Introduce KioskModeManager component #14586, [NET11 new API] Visual Styles feature (postponed from .NET 9 and .NET 10) #14587 for consistency (hard-wrapped vs. single-line-per-paragraph source style - both render identically on github.com, but consistency helps terminal/CLI review).
• Fix malformed C# in [NET 11 API Proposal] Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting #14583's API Proposal code block (GetSystemTextSize() -> SystemTextSize property; invalid SetSystemTextSizeAwareness signature) before implementation started.
• Investigate a TreeView.FullRowSelect rendering regression noticed during Visual Styles exploration; file a dedicated bug issue if reproduced independent of these proposals. Investigated: no regression found on main or Net11Api_05_VisualStylesMode (no TreeView file differences between them); current best diagnosis is the long-standing, already-documented native constraint that FullRowSelect has no visual effect while ShowLines is true (the WinForms default). Filed as Investigate TreeView.FullRowSelect appearing ineffective KlausLoeffelmann/winforms#13 for further confirmation/follow-up, not treated as a regression from this batch of work.

Branch summaries (as implemented)

• Net11Api_03_ImproveControlRendering ([.NET 11 API Proposal] Add APIs for performance improved, flicker-free WinForms UI mutation #14585): FormRevealMode (Inherit/Classic/Deferred) as a real Form-level ambient property backed by PropertyStore, resolving through Application.DefaultFormRevealMode/IsFormRevealDeferred; SuspendPaintingScope/SuspendRelocationScope as sealed class : IDisposable (async-await-safe); ISupportSuspendPainting/ISupportSuspendRelocation as explicit interface implementations on Control with protected ...Core() override hooks; DeferLocationChange removed entirely (see [API Proposal] DeferLocationChange - batch child-control location changes (split from #14585, postponed) KlausLoeffelmann/winforms#12). VB Application Framework wiring included. 3 commits, full targeted test pass (only a single pre-existing, unrelated DPI test failure reproduced independent of these changes).
• Net11Api_05_VisualStylesMode ([NET11 new API] Visual Styles feature (postponed from .NET 9 and .NET 10) #14587): added the missing VisualStylesMode.LatestPreview value; fixed a getter/setter coupling bug in the write-once SetDefaultVisualStylesMode; gated TextBoxBase.Padding to stay inert without a Net11+ opt-in; completed the VB Application Framework VisualStylesMode wiring. 3 commits.
• Net11Api_04_KioskManagerComponent ([.NET 11 API Proposal] Introduce KioskModeManager component #14586): fixed Site/ContainerControl auto-resolution semantics (including explicit-null handling), FullScreen init-time deferral and dispose-time restore, WakeUpCommand parameter (wake-source string), replaced a static SystemEvents dependency with form-local power/session observation, keyboard handling correctness, and ISupportInitialize side-effect deferral. 2 commits, 49/49 targeted tests passing. Confirmed as one of the lower-risk branches in this batch, per the original working hypothesis.
• Net11Api_01_New_Application_Api ([NET 11 API Proposal] Application.SystemTextSize - runtime awareness of the Accessibility text-scale setting #14583): full implementation from scratch (branch previously had only the drafting prompt) - Application.SystemTextSize/SystemTextSizeAwareness/SetSystemTextSizeAwareness/static SystemTextSizeChanged via the leak-safe SystemEvents.UserPreferenceChanged architecture, plus Form.SystemTextSizeChanged via each form's own WM_SETTINGCHANGE handling (mirroring the existing DPI-change architecture to avoid rooting hazards). Now also adds Application.GetWindowsAccentColor() (WinRT UISettings accent color via a hand-authored IUISettings3 ABI in Microsoft.Private.Windows.Core, no CsWinRT dependency; returns the OS default accent color when none is set), broadening the branch into the general "new Application API" bucket.
• Net11Api_02_TreeView_NodeLeading ([NET11 API Proposal] TreeView.NodeLeading - opt-in honest, text-scale-aware node-row height #14584): full implementation from scratch (new branch, none existed previously) - TreeView.NodeLeading with the legacy/honest ItemHeight split, TVS_NONEVENHEIGHT/handle-recreate wiring, Font/DPI-aware recompute, and full designer serialization support. 2 commits, all NodeLeading tests passing.