Microsoft promises to eventually make WinUI 'truly open source'

Microsoft lead software engineer Beth Pan has stated that WinUI, the modern user interface framework for Windows, will be made "truly open source," though no date is yet set because of deep entanglements with proprietary code in the operating system.

WinUI 3 is the framework introduced as part of Project Reunion in 2020, the company's effort to bring together developers who adopted the Universal Windows Platform, introduced with Windows 10, with those using the older Win32 API or .NET frameworks such as Windows Forms and Windows Presentation Foundation (WPF).

Project Reunion became the Windows App SDK (WASDK). WinUI supports Fluent Design, the Microsoft design system used for apps across Windows, web, and mobile.

The WinUI 3 gallery is an official demonstration of the UI framework, now to be made fully open source

Pan seemed to acknowledge the frustration of developers disappointed with the slow progress of WinUI, including many unfixed bugs and the lack of any visual designer for Visual Studio, and said that the team is entering a new phase of improvements including actively working toward "truly open sourcing the repo."

Currently, much of the WinUI code is periodically mirrored to GitHub, but the main repository is private to Microsoft. Pan set out four phases for the move to open source, beginning with more frequent mirroring, followed by the ability for third-party developers to build the code, then the ability to contribute pull requests and run tests locally, and finally making GitHub the primary repo.

The process is complex, she said, because of proprietary layers in Windows that need to be separated or shared.

Developers responding to Pan are largely positive about the open source move, but doubtful concerning whether Microsoft will now invest sufficient resources to build confidence.

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"I've been heavily invested in WinUI for years now," said one. "I don't think Microsoft understands the damage they have caused to the evangelists and wider developer community, along with the companies who have embraced the never-ending stagnation and false promises from WinRT-UWP-WinUI/WASDK."

Further complaints include buggy modal dialogs and no "working solution for input validation."

Another developer suggested that "the entire WinRT (and its follow-on WinUI) idea was a mistake," referencing the fracturing of Windows development that began when, in Windows 8, Microsoft chose to create a new Windows Runtime (WinRT) with projections (interop) enabling code in C++ or .NET languages.

Open sourcing WinUI is likely a positive move for the framework, yet what counts more is how much resource Microsoft is willing to dedicate to it. "How many people in total are assigned to the WinUI/WinAppSDK teams?" asked another developer, adding: "Today it feels like Web is the primary focus, and everything else is just maintenance." ®