MVVM Toolkit error MVVMTK0008

The source generator features from the MVVM Toolkit require consuming projects to set the C# language version to at least C# 8.0. Make sure to add <LangVersion>8.0</LangVersion> (or above) to your .csproj file.

To learn more about how to enable a newer C# version on older frameworks, see this blog post.

Note

While updating the C# language version will generally work with no issues, as the compiler has to be resilient to missing types and runtime features, using a newer C# version than the default one for a given framework/runtime is not officially supported. Make sure to test your application properly if you decide to manually override the language version in your projects.

The following sample generates MVVMTK0008:

<PropertyGroup>
    <LangVersion>7.3</LangVersion>
</PropertyGroup>

using CommunityToolkit.Mvvm.ComponentModel;

namespace MyApp;

// The project doesn't have a high enough version of C#
[INotifyPropertyChanged]
public partial class SampleViewModel
{
}

Additional resources

• You can find more examples in the unit tests.