How to access to Internal class converter in another assembly from XAML with "InternalsVisibleTo"

Question

I have something like this converter with the difference that class is internal and for security the converter belongs to another assembly (MyAssembly.dll):

namespace MyAssembly.InAnotherNameSpace
{
    internal class ValueConvertor : IValueConverter
        {        
            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
            {
                ...
            }

            public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
            {
                ....
            }
        }
}

And I use InternalsVisibleToAttribute to access the converter from a WPF project:

....
xmlns:c="clr-namespace:MyAssembly.InAnotherNameSpace;assembly=MyAssembly"
....
 <UserControl.Resources>
        <ResourceDictionary>
            <c:ValueConvertor x:Key="valueConvertor"/>
        </ResourceDictionary>
    </UserControl.Resources>

I have a problem in XAML, not recognize the class as internal and Visual Studio show this error:

Only public or internal classes can be used within markup. 'ValueConvertor' type is not public or internal.

Follow this answer thread, InternalsVisibleTo not working in XAML, that is true?

Why should it not be true, taking that fact into account that you experience the same problem? — Clemens, Mar 02 '20 at 21:36
@Clemens Because in that answer thread Ângelo Moreira asking: "Are you saying, that InternalsVisibleTo works only for C# but not for XAML?" and nobody affirms if it is true or false, so I suspect that nobody knows the answer, or is a WPF bug. — Ejrr1085, Mar 03 '20 at 00:48

score 1 · Accepted Answer · answered Mar 03 '20 at 08:21

1

you can apply a workaround - create converter in control code-behind and use it from XAML markup:

public partial class View : UserControl
{
    public static readonly IValueConverter valueConvertor = new MyAssembly.InAnotherNameSpace.ValueConvertor();

    public View()
    {
        InitializeComponent();
    }
}

<TextBlock Text="{Binding Something, Converter={x:Static local:View.valueConvertor}}"/>

answered Mar 03 '20 at 08:21

ASh

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Ok, so I must create public copy properties, because XAML only working with public properties. Nice solution, thank you!. – Ejrr1085 Mar 03 '20 at 16:25
@Ejrr1085, note that I used *static* field, which can be accessed via `{x:Static}` extension. Instance properties will require binding, which is not supported inside `{Binding}` expression. And yes, they have to be public. – ASh Mar 03 '20 at 16:42
Or you can use `Converter={DynamicResource valueConvertor}` and add converter to control Resources in code-behind, or anywhere really – ASh Mar 03 '20 at 16:44
Thank you very match. – Ejrr1085 Mar 03 '20 at 21:20

score 0 · Answer 2 · answered Mar 03 '20 at 14:50

You can use an internal class in another assembly with InternalsVisibleTo(). Confirmed it with VS2019 and .net 4.7.2.

The VS2019 XAML editor complains throws a few errors but runs just fine.

XDG0009 - The type "UserControl1" is not accessible.)
XLS0419 - Undefined CLR namespace. The 'clr-namespace' URI refers to a namespace 'WpfControlLibrary2' that could not be found

This seems just a limitation of VS XAML Editor.

How to access to Internal class converter in another assembly from XAML with "InternalsVisibleTo"

2 Answers2