.NETpad 2025: A Look Ahead to .NET 10 (Premium)

In 2024, Microsoft brought the Windows Presentation Foundation (WPF) back from the dead as part of .NET 9, adding Windows 11 theming support and a few other improvements. But its work was half-assed, with many bugs and functional omissions, including some I experienced and documented as part of my .NETpad modernization efforts. And so my hope for 2025, as I continue that work, is that Microsoft will address at least some of the many problems it introduced and advance WPF further, making it even more of a viable option for developers looking to create or update Windows apps.

I know. Naive.

What's the saying about doing the same thing repeatedly and expecting a different outcome? I went into my .NETpad modernization work full of excitement, expecting Microsoft to follow up its initial pre-release support for WPF Windows 11 theming with more new features and improvements and, as importantly, the documentation to back it up. And so I plowed forward, knowing it could only get better.

It never got better.

Microsoft released its initial support for WPF Windows 11 theming in .NET 9 Preview 5 the week of Build 2025 ... and then never once provided any further documentation or functional updates. It pushed forward with a steady cadence of .NET 9 preview releases throughout the summer, and then a series of release candidates that fall. But it never once updated WPF or its support for Windows 11. Not once.

So I did what I could. I focused on what I could get done in 2024 with the tools Microsoft provided, bugs and all. And by the time .NET 9 arrived right on cue in November, I was resigned to what I still see as an unprofessional lack of documentation and support. But I was surprised to discover that Microsoft finally documented a few additional features for WPF developers targeting Windows 11 theming in the initial stable release of .NET 9. And then further surprised when I discovered a few other changes, including the ability to change the app theme dynamically at runtime, a key feature I needed.

I'm not a professional developer, a point I try to drive home every time I tackle a particularly thorny topic. And after discovering the aforementioned feature, I was surprised to discover that .NETpad crashed repeatedly when I implemented it in the app. Naturally, I assumed it was me. And I spent (wasted) weeks, literally, trying to figure out what I had done wrong. Eventually, I discovered that it was tied to the WPF Expander control I was using--because that's what Notepad uses, God damn it--in the settings interface. If I changed the app theme dynamically at runtime while using (or, oddly, after using) an Expander, it would crash. If there was no Expander, it worked fine. Huh.

I Googled this, as one would. And I what I eventually learned was that this was Microsoft's fault: The bug was in the WPF code tied to Windows 11 theming. Microsoft acknowledged the bug, fixed it internally, and marked the issue closed. So I asked, "where" was...