At Build 2020, Microsoft announced Project Reunion with the aim of unifying app development across multiple Windows 10 versions and devices. The first three components of Project Reunion available to developers in preview are WinUI 3, WebView2 and MSIX (MSIX-Core).
Project Reunion makes it easier to build a great Windows app by providing a unified platform for new and existing Win32 and UWP apps. It will unify access to existing Win32 and UWP APIs and make them available decoupled from the OS, via tools like NuGet.
As the following picture clarifies, with Project Reunion Microsoft is working to build new APIs on top of existing Win32 and UWP APIs to provide a common API layer independent from the underlying OS. Microsoft will distribute the new API as independent packages that can be bundled along with apps and used on a variety of Windows versions.
(Image courtesy of Microsoft)
As mentioned, one of the first Project Reunion component is WinUI 3, a framework to build graphical user interfaces for Windows apps.
Technically, WinUI 3 decouples the XAML, Composition, and Input layers of Windows 10, and ships them independently via NuGet for any app targeting Windows 10 1803 and above. It can be used in both C++ and .NET-based apps.
Project Reunion packages are not limited to decoupling existing APIs and making them available through packages, but can also add new features. As an example of that, WinUI 3 includes a new SwapChainPanel control to enable better integration with DirectX, as well as a new Chromium-based WebView2 control.
Another component already available with Project Reunion is MSIX, Microsoft package format, which will provide the foundation for Project Reunion package distribution. A new feature introduced in MSIX is MSIX App Attach, meant to make it easier for developers to create apps that can work with Windows Virtual Desktop:
The MSIX App Attach Preview will optimize people’s experiences by untangling the OS image that organizations deploy in the cloud from the apps that people need to access.
According to Microsoft, apps using MSIX App Attach can be ported seamlessly from the desktop to Azure-based Windows Virtual Desktop.
Work on Project Reunion will extend across multiple years, according to Microsoft official roadmap. No new components are planned to be released in 2020, although Microsoft intends to have an overarching preview of Project Reunion ready by the end of this year.
