Microsoft is Moving File Explorer to the Windows App SDK

In an unexpected move, Microsoft said this week that it will transition the Windows 11 File Explorer app to the Windows App SDK, a potentially monumental change that could break compatibility with apps that integrate with this key system app.

News of the change came during a live WinUI Community Call and was first reported by Rafael Rivera.

“We wanted to share some news with File Explorer,” Microsoft WinUI product manager Gabby Bilka said during the call. “We’ve been working really closely with the File Explorer team over the last year-plus to migrate that app to WinAppSDK and WinUI 3. File Explorer on WinAppSDK is going to be available soon in the Windows Insider Preview Program. It looks similar to the Windows 11 File Explorer that you use today.” (It looks identical.)

To understand what this change means, one first needs to understand how Microsoft created the current version of File Explorer: this is a decades-old classic desktop application that was skinned with WinUI 2 in Windows 11 using a private version of a technology called XAML Islands to give it a more modern look and feel. To transition this app to the Windows App SDK and WinUI 3, Microsoft will most likely have to rewrite it from scratch. And doing so would likely break File Explorer’s extensibility model. The most obvious victims are cloud storage services like Box, Dropbox, and Google Drive, unless of course Microsoft has figured out a way to bring these things forward to the new app.

Windows App SDK is the successor to the deprecated Universal Windows Platform (UWP). It solves some of the problems with UWP, the most obvious being that each UWP version was tied to a specific Windows 10 version, creating headaches for developers that wanted to use specific features. And it advances its user interface functionality to WinUI 3, where UWP is stuck on the older WinUI 2. But WinAppSDK also introduces some new limitations, the most obvious being that, unlike with UWP, WinAppSDK apps only run on Windows; they are not compatible with Xbox, HoloLens, or other UWP-compatible platforms.

The issue with the current versions of File Explorer is that XAML Islands is complex and hard to work with. But as most people following Windows 11 have noticed, Microsoft has screwed around with File Explorer a lot: there have been three distinct versions of this app since Windows 11 first shipped in October 2021, each with its own UI tweaks. And it appears that Microsoft wants to keep messing with the File Explorer UI, and they have decided internally that migrating to WinAppSDK is the only way to do what they want to do. (At least easily.)

Very interesting.