The latest version of the Uno Platform was unveiled at UnoConf. Uno is a UI platform that uses C# and WinUI and can be used with single-codebase applications across Windows, WebAssembly, iOS, macOS, Android, and Linux. 

One major addition in Uno Platform 4.0 is Uno Extensions, which is based on Microsoft Extensions, which are capabilities that Microsoft extracted from ASP.NET and made them available elsewhere. According to Uno, the idea behind Uno Extensions is that developers shouldn’t have to rewrite code for commonly used functions.

There are about 10 extensions currently available, and one of the main ones is Reactive (MVU-X), which allows for the different states that data can go through to be packaged and sent through a dedicated interface called a Feed. 

Navigation is another extension and it provides a paradigm for different types of navigation, including frame-based, modal, selecting a view item, pickers, returning data, and dynamically adding views to regions. 

This release also introduces a preview of a new Visual Studio Code Plugin and Codespaces Integration, which offers benefits like XAML Code Completion, XAML Hot Reload, WebAssembly C# debugging, and more. 

Uno Toolkit was also introduced in this release. Uno Toolkit is a set of multiplatform components that WinUI doesn’t offer out-of-the-box, such as NavigationBar, which is a cross-platform navigation solution, and TabBar, which is a primitive control that provides a list of selectable items. 

More information about what’s new in this release, as well as the breaking changes that were introduced, can be found here.