WPF VS2022 无法检查 targettype 是否为 Visibility

Question

I have a IValueConverter that converts "null" to "Visible":

public class InverseNullToVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        if (targetType != typeof(System.Windows.Visibility))
            throw new InvalidOperationException("The target must be a Visibility");
        
        if (value == null)
            return Visibility.Visible;

        return Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

This worked fine in Visual Studio 2019 , however when i updated to 2022 i got error on every place that used this valueconverter. The first if-case ALWAYS returns true, no matter what input is given.

Why does not "if (targetType.= typeof(System.Windows.Visibility))" work in VS 2022? What should i change to make it work?

Im using .Net Framework 4.7.2.

The error message that i receive is XDG0066 , it has no text other than the text i provide in the throw "The target must be a Visibility"

An example of where i used the valueconverter:

<Rectangle x:Name="Back" Fill="{TemplateBinding Background}" Visibility="{TemplateBinding ImageBack, Converter={StaticResource InverseNullToVisibilityConverter}}"/>

Answer 1

It is a problem in the XAML designer, which seems to apply your converter in a context where the target type is not exactly Visibility .

Change your check to a more generally applicable expression, like

if (!targetType.IsAssignableFrom(typeof(Visibility)))
{
    throw new InvalidOperationException("The target must be assignable from Visibility");
}