WinUIRichEditor

A from-scratch rich text editor control for WinUI 3, rendered with Win2D (CanvasVirtualControl / CanvasTextLayout). It is a port of AvaloniaRichEditor — the same document model, formatters, and "single TextLayout is the source of truth" engine design, rebuilt on the DirectWrite-backed CanvasTextLayout instead of Avalonia's TextLayout.

Status: converged with AvaloniaRichEditor — feature parity in both directions. Beyond matching the original's feature set, the two projects have since exchanged improvements both ways (a source-compatible alias layer here, platform-agnostic features back-ported there), and the original's own full-source audit has been swept against this codebase. Tables, images, formatting, clipboard, page view, print/PDF, the drop-in host controls, localization and accessibility all work, including the edge cases (nested/inline-table row·column resize, full keyboard caret traversal through inline-table cells). Native AOT publish works end-to-end (self-contained — builds, runs, renders; re-verified each release). The document format is byte-compatible with AvaloniaRichEditor (verified by loading a .flow saved by the original). See Project_Roadmap.md and CHANGELOG.md. The control API may still change.

Requires Windows App SDK 2.3.2 or later. (Raised from 2.2.1 in 0.9.0 — see the CHANGELOG for the other behavioural changes in that release.)

Tech stack

• .NET 10 (net10.0-windows10.0.26100.0), C# nullable enable. Target: unpackaged (no MSIX).
• WinUI 3 / Windows App SDK 2.3.x — the library references the split Microsoft.WindowsAppSDK.WinUI package (2.3.2); controls are code-only (no XAML, avoids AOT compiled-binding pitfalls).
• Win2D 1.4.0 (Microsoft.Graphics.Win2D) — immediate-mode rendering; one CanvasTextLayout per paragraph drives render, caret, hit-testing, and selection.
• HtmlAgilityPack 1.12.4 for external HTML paste parsing.

Features

Text & formatting

• Bold / italic / underline / strikethrough, font family & size, foreground & highlight color, clear formatting
• Paragraph alignment, headings (H1–H6), blockquote, indent, bullet / numbered lists, custom line spacing
• Hyperlinks (insert / edit / open / remove), format painter
• Caret + drag/Shift selection, double-click word / triple-click paragraph select, undo/redo
• Keyboard: arrows, Home/End (visual line), Ctrl+←/→ word, Ctrl+Home/End document, Ctrl+Backspace/Delete word delete, PageUp/PageDown, and shortcuts (Ctrl+B/I/U, Ctrl+Z/Y, Ctrl+C/X/V, Ctrl+Shift+V plain paste)
• Korean / CJK IME composition (inline underline) via CoreTextEditContext

Tables

• colspan/rowspan, nested tables, recursive cell content (paragraphs, images, dividers, nested tables)
• Tab cell navigation, right-click row/column insert·delete, cell merge/split, drag-select cells
• Draw-to-size insert (toolbar grid picker), column-width & row-height resize (drag borders), table block selection, block↔inline ("treat as character") toggle

Images

• Block & inline rendering (async GPU decode), insert from file, clipboard image paste, drag-and-drop image files
• Click-to-select with resize handles (aspect-locked), right-click copy / size presets / replace / save / delete

Clipboard & I/O

• Internal rich copy/paste, RTF, external HTML (CF_HTML), image, and Excel/TSV→table paste; plain-text paste (Ctrl+Shift+V); copy a selected image to the system clipboard
• File formats: .flow (ZIP package), .json, .html, .rtf, PDF export — see the document format spec (byte-compatible with AvaloniaRichEditor)

Page view, print & PDF

• PageSize / PageOrientation / ShowPageBoundaries, stacked page view with line-aware page breaks, headers / footers / page numbers
• RenderPrintPage(i, dpi) (offscreen bitmap) and SavePdf(stream) (rasterized pages → PDF)

Host controls & chrome

• Drop-in RichEditorView (toolbar + page/zoom chrome + editor + status bar + Export/Import/Print) and a standalone RichEditorToolbar (LeadingItems/TrailingItems host slots, wrap-on-narrow)
• Icon theming: built-in Segoe Fluent Icons glyphs, host-overridable per slot via RichEditorIcons.Provider
• Capability: IsReadOnly (a viewer is IsReadOnly=true + no/minimal toolbar) + feature flags (AllowImages / AllowTables / AllowRichPaste). Toolbar density via ToolbarLevel (Minimal / Normal / Maximum)
• Word-standard keyboard shortcuts from a single table (RichEditorShortcuts), shown in menu hints + toolbar tooltips
• Localization (KO / EN, host-extensible) via RichEditorLocalization; accessibility peer (IValueProvider)
• Change events (TextChanged / SelectionChanged / DocumentChanged) and appearance DPs (SelectionBrush / CaretBrush)

Quick start

Drop-in host control (toolbar + editor + status bar):

using WinUIRichEditor.Controls;
using WinUIRichEditor.Formatters;

var view = new RichEditorView();
view.Document = HtmlDocumentFormatter.ParseHtml("<h1>Title</h1><p>Hello <b>world</b></p>");
// view.IsReadOnly = true;  // make it a viewer

// the toolbar's image button needs a host file picker (window handle required, unpackaged):
view.ImagePicker = async () => /* return image bytes, or null */;

// page view + export
view.Editor.PageSize = RichEditorPageSize.A4;
using var pdf = new MemoryStream();
view.Editor.SavePdf(pdf);

Bare control:

var editor = new RichEditor();
editor.Document = HtmlDocumentFormatter.ParseHtml("<p>Hello <b>world</b></p>");
editor.ToggleBold();                       // operates on the selection / caret word
editor.SetForeground(Windows.UI.Color.FromArgb(255, 204, 0, 0));

string json = editor.ToJson();             // also ToHtml / ToRtf / SavePackageAsync
editor.LoadHtml("<p>replaced</p>");

Controls are code-only — a no-XAML Page crashes WinUI 3 navigation, so host them in a XAML-shell page (see samples/.../ViewDemoPage.xaml). File pickers need HWND interop (InitializeWithWindow).

Build, test & run

dotnet build WinUIRichEditor.slnx
dotnet test  tests/WinUIRichEditor.Tests/WinUIRichEditor.Tests.csproj   # 26 headless model/formatter tests
dotnet build samples/WinUIRichEditor.Demo/WinUIRichEditor.Demo.csproj
# run the unpackaged exe directly:
#   samples/WinUIRichEditor.Demo/bin/Debug/net10.0-windows10.0.26100.0/win-x64/WinUIRichEditor.Demo.exe

A running instance locks the exe — stop it before rebuilding: Get-Process -Name "WinUIRichEditor.Demo" | Stop-Process -Force.

The demo is a four-page nav shell, one per library layer: 컨트롤 (bare RichEditor), 읽기 전용 (IsReadOnly=true), 컨트롤+툴바 (RichEditor + RichEditorToolbar), and View (full RichEditorView with page/zoom chrome, status bar, Export/Import/Print, and PDF export).

Native AOT

Native AOT publish works end-to-end. The library is AOT-shaped (source-gen JSON, no reflection serialization, code-only control, IsAotCompatible, no WinRT-static activation in the model/formatter layer), and the self-contained profile (samples/.../PublishProfiles/win-x64.pubxml: PublishAot + SelfContained + PublishSingleFile + PublishTrimmed, WindowsAppSDKSelfContained=true) builds cleanly (~13 MB native exe, 0 trim/AOT warnings), runs, and renders — Win2D CanvasTextLayout, CanvasDevice, and CanvasFontSet all activate under AOT. (An earlier "crashes at startup in combase 0x80004005" was a framework-dependent-only limitation; the self-contained bundle supplies WinRT activation.)

Build workaround (still required): GenerateLibraryLayout on the library plus an MSBuild target that strips the stale windowsappsdk.winui\1.8 PRIs (pulled in transitively by Win2D 1.4.0) clears the PRI277 conflict with Windows App SDK 2.2's PRI. Removable once a WinAppSDK-2.x-aligned Win2D ships.

Project layout

Path	Contents
src/WinUIRichEditor	Control library: Controls, document model Documents, Formatters.
samples/WinUIRichEditor.Demo	Unpackaged WinExe demo: four-page nav shell (control / read-only / control+toolbar / view).
tests/WinUIRichEditor.Tests	Headless xUnit tests for the model + formatters (dotnet test).

License

MIT © 2026 centwon. Depends on the Windows App SDK, Win2D, and HtmlAgilityPack (all MIT) — see THIRD-PARTY-NOTICES.md.