Edit

Windows App SDK platform overview

The Windows App SDK supports two languages for app development: C# and C++. Each language uses a language projection to call Windows Runtime (WinRT) APIs, and both use XAML (specifically WinUI 3 XAML, in the Microsoft.UI.Xaml namespace) to define the user interface. Together, these projections and the UI framework form the platform layer.

Note

C# and C++ are the only languages with supported projections for Windows App SDK and WinUI 3. Community projects exist for other languages (such as Rust), but they are not officially supported.

Do you need to know about this?

If you create a project from the standard Visual Studio templates for Windows App SDK or WinUI 3, the language projection is already configured for you. Your C# or C++ code can call WinRT APIs directly, and you don't need to think about how the projection works.

You typically need to look deeper into the projection layer when you:

  • Author a Windows Runtime component that other apps or languages consume.
  • Distribute a library as a NuGet package that wraps WinRT APIs.
  • Interop with low-level COM or ABI interfaces from C++ code.
  • Troubleshoot build errors related to generated interop code or WinMD files.

For everyday app development, the details below are background knowledge — useful if you're curious, but not required to get started.

Language projections

Windows Runtime APIs are defined in a language-neutral way using Windows Metadata (.winmd) files. A language projection reads that metadata and generates idiomatic bindings so you can call the APIs naturally from C++ or C#.

Projection Language What it is Namespace pattern
C++/WinRT C++17 A header-only library that provides first-class access to WinRT APIs. It replaces C++/CX and the Windows Runtime C++ Template Library (WRL). winrt::Microsoft::UI::Xaml
C#/WinRT C# (.NET) A NuGet-packaged toolkit that generates .NET interop assemblies from .winmd files. It enables you to consume, and author, WinRT components from C#. Microsoft.UI.Xaml

UI framework

Framework What it is Namespace
XAML (WinUI 3) The declarative XML-based markup language for WinUI 3 user interfaces. Handles layout, styling, data binding, and animations. Code-behind is written in C# or C++. Microsoft.UI.Xaml (not Windows.UI.Xaml, which is UWP)

Important

WinUI 3 XAML uses the Microsoft.UI.Xaml namespace. If you see code or documentation referencing Windows.UI.Xaml, that is UWP XAML, which is a different framework. Do not mix the two namespaces in a WinUI 3 project.

Next steps

Choose the area that matches what you want to learn:

  • Last updated on