WPF .Net Core 3.0 mapping language primitive types in Xaml

Question

One of the issues I'm facing while converting WPF application from NET Framework 4.7 to .Net Core 3.0 is a problem with mapping primitive types like Double in XAML. In NET Framework this XAML has worked perfectly:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    >

   <sys:Double x:Key="BaseSize">10</sys:Double>
</ResourceDictionary>

However mscorlib does not exist in .Net Core. How can I map primitive types in XAML in .Net Core 3?

Had tried this: https://docs.microsoft.com/en-us/dotnet/framework/xaml-services/built-in-types-for-common-xaml-language-primitives

But for WPF this does not work as it is stated here:

"In WPF, you can use XAML 2009 features but only for XAML that is not markup-compiled. Markup-compiled XAML for WPF and the BAML form of XAML do not currently support the XAML 2009 keywords and features."

Answer 1

You can use the exact same markup when targeting .NET Core 3.0, i.e. xmlns:sys="clr-namespace:System;assembly=mscorlib" does actually work. Any reference to mscorlib is type forwarded to System.Runtime automatically.

Try to build the solution or take a look at this GitHub issue if you don't believe me.

Edit: Starting with .NET Core 3.1, you should replace assembly=mscorlib with assembly=System.Runtime.