VB WinUI 3 Demos

Demonstrates how to use WinUI 3 in Visual Basic .NET projects.

Status

Works, verified with Visual Studio and with dotnet build on .NET 10:

• XAML compilation by the forked compiler, including the Sub Main entry point - a VB project needs no Program.vb.
• XBF generation, running self-contained without MSIX, Mica/Acrylic, WinForms host integration (HostServices.VBHost).
• BatchFfmpegWinUI builds warning-clean (0 warnings, 0 errors) and shows its window; all three of its XAML files compile.
• BatchFfmpegWinUI binds with x:Bind, including x:DataType templates.

Progress

• No C# or C++ projects for startup
• Load XamlControlsResources from Microsoft.UI.Xaml.Controls automatically
• Let the XAML compiler generate the entry point - no Program.vb is needed; DISABLE_XAML_GENERATED_MAIN remains available for taking the entry point over manually.
• Allow Windows Forms integration, such as registering HostServices.VBHost at startup
• Make sure Mica and Acrylic are working as expected on Windows 11
• Workaround blocking bugs of the WinUI 3 XAML compiler - Generate Xbf files and VB source files
• Run apps without MSIX packaging
• Use a custom XAML compiler (Approach 3) - see Custom XAML compiler
• Publish a NuGet package that contains VB specific build transitive files, so any VB projects will be able to use WinUI 3 without editing *.vbproj manually.
• Publish a VSIX to add VB WinUI 3 templates to Visual Studio.
• Write a new VB application framework for WinUI 3 - Allow users to delete Program.vb and use events to configure the App in the Application class
• Write a new VB "My extension" for WinUI 3 - Enable My.* for WinUI 3 specific things

Environment

• Visual Studio 2026 with Windows Desktop and WinUI development workloads
• Windows 10 21H2+ or Windows 11

Build

vbxamlc is a submodule that holds the compiler and the local NuGet feed. Its nupkg is not committed, so pack it once:

git submodule update --init --recursive
cd vbxamlc
msbuild XamlCompilerPrerequisites.sln /p:Configuration=Release /p:Platform=x64 /restore /m
build\xamlcompiler-nupkg\pack.cmd
cd ..

Then build BatchFfmpegWinUI.sln in Visual Studio, or:

dotnet build BatchFfmpegWinUI\BatchFfmpegWinUI.vbproj -c Debug -p:Platform=x64

If the compiler build stops with MSB4019 about Microsoft.MSBuildCache.Local, run vbxamlc\init.cmd once (or put that package under vbxamlc\packages\).

To check which compiler was used: the build log prints VBWinUI3 XamlCompiler override active: ... with paths under the package, and generated files carry the 3.0.0.0 stamp (the stock compiler stamps 3.0.0.2606). Repacking, version bumps and cache rules are in vbxamlc\build\xamlcompiler-nupkg\readme.md.

How does it work

• Approach 1 - VB workarounds: two MSBuild files (WinUI3.VisualBasic.props / .targets) that BatchFfmpegWinUI imports through Directory.Build.props.
• Approach 2 - C# compiler plus code converter: abandoned, see XamlLanguageConverter.
• Approach 3 - custom XAML compiler: what this repository uses. Details below.

Custom XAML compiler

The XAML compiler comes from winui3-vbxamlc, whose Visual Basic code generators are fixed, and is consumed as a compiler-only NuGet package. The package replaces three tool paths of the stock WinUI package and leaves its targets, genxbf and reference assemblies in place.

Using it in another VB project

Reference Microsoft.WindowsAppSDK and Nukepayload2.UI.VBWinUI3 - nothing else:

Package	Purpose
Nukepayload2.UI.VBWinUI3	VB build support: ImportFrameworkWinFXTargets, VBRuntime=None for XamlPreCompile, reg-free WinRT initializer for self-contained apps
Nukepayload2.UI.VBWinUI3.XamlCompiler	redirects the XAML compiler to the fork; arrives as a dependency of the package above

Everything BatchFfmpegWinUI imports by hand (WinUI3.VisualBasic.props, WinUI3.VisualBasic.targets and include\UndockedRegFreeWinRTAutoInitializer.vb) ships under buildTransitive\, named after the package id, so NuGet imports it automatically - there is nothing to copy from this repository and nothing to Import.

BatchFfmpegWinUI itself stays on the source-tree import instead of referencing the package: it is the development project these files and the compiler are built from.

0.10.0-beta no longer defines DISABLE_XAML_GENERATED_MAIN, so the compiler generates Program and Sub Main itself; delete the entry point you had to write for 0.9.4-beta.

This repository's nuget.config adds vbxamlc\PackageStore as a feed: that is where the sample picks up compiler packages built from the submodule, before they are pushed.

Samples

BatchFfmpegWinUI

A mp4 video to h265 transcoder.

It converts .mp4 and .mkv videos to h265 encoding by calling H265.bat.

Status

✅ Builds and runs with Windows App SDK 2.5.1.

How to use it

• Install ffmpeg to %programfiles%\ffmpeg\bin. If you have installed it in a different location, please add it to %PATH%.
• Open BatchFfmpegWinUI.sln with Visual Studio.
• Set BatchFfmpegWinUI_Pack as startup project and run.
• Drag and drop .mp4 or .mkv files.
• Press the "Convert" button and wait.

XamlLanguageConverter

Demonstrates how to use MSBuild extension points to invoke the C# XAML compiler and start a code converter to convert the C# output to VB.

Status

❌ Stopped with error. Because it has severe performance issues.