Microsoft has released preview 6 of .NET 11, for which release is expected in November, including a big change to MAUI (Multi-platform App UI): it now runs only on .NET Core, rather than the Mono runtime.

Principal product manager David Ortinau reports that “your app builds and runs on CoreCLR, the same runtime behind ASP.NET Core, your cloud services, and desktop .NET.”

According to Ortinau, performance is generally faster than Mono on iOS and Mac Catalyst. The implication is that it is slower on Android, though he does say that it is within 10% on startup and app size. Selecting Mono is no longer an option, and the only use of Mono in .NET 11 is for Blazor WebAssembly.

There is a key remark in Ortinau’s post. “We have worked closely with first party .NET MAUI apps validating our progress, and have received feedback from several others,” he says. The question developers may ask: what first party .NET MAUI apps? Microsoft does not use MAUI for its well-known cross-platform apps such as Teams or Office. In 2023, the company said it uses MAUI for its 365 admin, Azure admin and Store Commerce apps, though I do not know if this is still the case.

Developers would have more confidence in MAUI, both for its quality and its long-term future, if Microsoft itself made more use of it.

That said, the company does seem to be putting substantial effort into MAUI for .NET 11. Along with the CoreCLR work there are other updates in this preview. Microsoft states that the focus in .NET 11 is “to improve product quality” and this is something developers will be happy about; in some cases a statement like this might imply neglect but for MAUI it is exactly what is needed.

I have a demo MAUI project and decided to upgrade it to the new preview, working with Visual Studio Code on a Mac. It was not as easy as I had hoped. The process involved not only updating the target framework, but also the minimum versions of Android, iOS and Mac Catalyst. Then the Android SDK had to be updated, with an annoyance related to the recommended:

dotnet build -t:InstallAndroidDependencies -f net11.0-android “-p:AndroidSdkDirectory=[your path to the Android SDKs]”

The command failed with an error about the Android SDK licenses not being accepted. The fix is to set an environment variable:

export AcceptAndroidSDKLicenses=True

and then it works, though I’m not sure how this satisfies the lawyers. I also had an error where

builder.Logging.AddDebug();

could not find the AddDebug method; the fix was to add a package reference to Microsoft.Extensions.Logging.Debug to the .csproj file.

With all that done, the “Start debugging” command is not working for me in VS Code. I get a message that the “configured debug type ‘coreclr_mobile’ is not supported, and an instruction to install coreclr_mobile Extension; clicking this button gets me “no extensions found.” Update – this was resolved after updating both the C# and C# Dev Kit extensions to pre-release versions (.NET MAUI was already pre-release).

However, dotnet run from the command line works:

I plan to do some more experimentation; note that this is a preview of .NET so some friction is expected.