Binding GradientStop works but reports error

Question

The following code binds a GradientStop to the Background.Color property of TemplatedParent. Everything works but I am getting a bindi

Answer 1

I also had the same error in the Visual Studio console output.

A possible explanation and workaround for this is reported here

Basically if you use a Converter that returns a LinearGradientBrush then you don't get the error

The code is something like this

[ValueConversion(typeof(System.Windows.Media.Color), typeof(LinearGradientBrush))]
class GradientConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var brush = new LinearGradientBrush();
        var color = (Color)value;
        brush.StartPoint = new Point(0.5, 0);
        brush.EndPoint = new Point(0.5, 1);

        brush.GradientStops.Add(new GradientStop(Colors.White, 0));
        brush.GradientStops.Add(new GradientStop((Color)value, 1));

        return brush;
    }

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

And in the XAML

<Border BorderThickness="1" BorderBrush="{TemplateBinding Background}" Background="{Binding Path=Background.Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource gradConv}}">