Microsoft Will Let Developers Update Legacy UWP Apps to .NET 9

Microsoft today announced a surprising new modernization path for developers stuck supporting legacy UWP apps. Instead of full-on migration to the Windows App SDK, which can be complex and time consuming, developers will soon be able to upgrade their existing UWP apps to .NET 9, a half-step forward of sorts that will enable various low-level advantages. Then they can later continue their modernization efforts using UWP XAML Islands or go all-in with the Windows App SDK to gain access to the most modern controls and capabilities.

“UWP support for .NET 9 and Native AOT provides a path for existing UWP developers to modernize their apps using the latest version of .NET.,” Microsoft’s Sergio Pedri explains. “[It] does not introduce any new features for UWP. Instead, it provides a migration path for developers to modernize their apps with .NET 9 while they consider moving toward WinUI 3 [part of the Windows App SDK]. It is rather a way for UWP app developers to modernize their apps and leverage all the recent advancements in .NET and C#, while still retaining the existing features that UWP provides today.”

This is an interesting and unexpected development that was no doubt inspired by the same conditions that caused Microsoft to bring WPF back from the dead: Despite wanting to move on to more modern app frameworks and capabilities, there are lots of these apps out in the world and their developers would like to keep them as up-to-date as possible. UWP is particularly problematic because its a mobile app framework that Microsoft has abandoned, and it’s stuck on .NET version 6. Migrating UWP apps to the desktop-based Windows App SDK can thus be difficult.

By supporting .NET 9 in UWP, Microsoft is hoping to soften the blow. Developers can upgrade their apps incrementally by modernizing the underlying code base first, removing dependencies on .NET Native (which is stuck at the .NET Core 2.0 feature level), access the latest .NET and C# features, and receive impressive performance improvements. Then they can later take the additional step of migrating to the UWP XAML Islands, which has its own issues, or the full Windows App SDK, by which those apps can take advantage of WinUI 3 and the other desktop-based advances Microsoft has made in the years since it killed UWP.

UWP support for .NET 9 is currently available in early preview–which makes sense since .NET 9 itself is still in preview–and there are likely all kinds of issues, plus some missing features. But if you want to get started now, or just want to see what to expect, you can learn more in the original post.