FabWinUI Designer

A standalone visual form designer for WinUI 3 — a WinForms/WPF-designer-style tool (toolbox, drag-to-place, property grid, live XAML source view) for a platform that doesn't ship one of its own.

Goal

WinUI 3 has no built-in visual designer comparable to the WinForms or WPF ones — Visual Studio's XAML editor is text-first, with only a passive preview. This project is a "simple," standalone app to place controls, edit their properties, and generate/round-trip real, hand-editable .xaml files, in the spirit of those older designers.

What it does

• Renders a real, live WinUI 3 tree on the design surface (via XamlReader.Load), not a drawn approximation.
• Round-trips genuine hand-editable .xaml files (XDocument-based) — no proprietary project format.
• Click-to-add toolbox, drag-to-move, 8-handle resize, and a reflection-driven property grid, all backed by an in-app undo/redo stack.
• A two-way-synced, syntax-highlighted XAML source view sits alongside the design surface: edit either one and the other follows, with inline error reporting for invalid XAML and a one-click reformat.

What's supported

Area	Support
Controls	Button, TextBlock, TextBox, CheckBox, ComboBox, Image, StackPanel, Grid
Layout	Canvas-based absolute positioning (Canvas.Left/Top, Width/Height) for v1
Selection	Single-select, move, 8-handle resize
Properties	Reflection-driven property grid (curated per-type list, no design-time metadata exists on WinUI controls to discover this automatically)
XAML source	Editable, syntax-highlighted, two-way caret sync with the design surface, inline error reporting, Format Document
File I/O	Open/New/Save, folder-based file browser, Recent Files/Folders
Undo/Redo	Whole-document snapshots
Not yet	Multi-select, data binding UI, event-handler code generation (planned next — see below)

Requirements

• .NET 10 SDK
• Windows 10/11 SDK 10.0.19041.0 or later
• Visual Studio 2026 (recommended for day-to-day editing; not required for the CLI build below)

See docs/dev-setup.md for full setup details, including the .sln vs .slnx note and pinned package versions.

Building and running

dotnet build FabWinUIDesigner.sln -p:Configuration=Debug -p:Platform=x64
dotnet build src/FabWinUIDesigner.App/FabWinUIDesigner.App.csproj -p:Platform=x64
./src/FabWinUIDesigner.App/bin/x64/Debug/net10.0-windows10.0.19041.0/FabWinUIDesigner.App.exe

dotnet test tests/FabWinUIDesigner.Document.Tests/FabWinUIDesigner.Document.Tests.csproj
dotnet test tests/FabWinUIDesigner.CodeGen.Tests/FabWinUIDesigner.CodeGen.Tests.csproj

Project layout

• src/FabWinUIDesigner.Document — the XAML document model (XDocument-backed), no WinUI dependency.
• src/FabWinUIDesigner.CodeGen — Roslyn-based code generation, no WinUI dependency.
• src/FabWinUIDesigner.Core — WinUI-dependent designer logic (live-tree correlation, property grid schema, preview loading).
• src/FabWinUIDesigner.App — the WinUI 3 application shell.
• tests/ — MSTest projects for the two pure-.NET layers.
• samples/ — example .xaml files used by the app and its tests.

Syntax highlighting

The XAML source view uses TextControlBox-WinUI (MIT) with a custom highlighting scheme matching Visual Studio's classic XML/XAML editor palette.

What's next

Event-handler code generation: wiring a XAML event (e.g. a Button.Click) to a Roslyn-generated stub inserted into the paired .xaml.cs partial class.

License

MIT — see LICENSE.