Binding Converter with paramater in one line syntax

Question

I am basically trying to formulate the following Binding conditions in one line/tag:

<Rectangle.Fill>
     <Binding Path="Contents.Value">
          <Binding.Converter>
               <localVM:SquareConverter Empty="White" Filled="Black" Unknown="Gray"/>
           </Binding.Converter>
      </Binding>
</Rectangle.Fill>

I can't seem to figure out how to specify the parameters above Empty="white" Filled="Black" Unkown="gray"

What I have so far:

 <Button Background="{Binding Path=Contents.Value, Converter={StaticResource localVM:SquareConverter}, ConverterParameter={ }}">

I give it the resource fine I think, now I can't find out how to specify the parameters syntactically correct?

P.S. Don't worry about the context, the button background is mapped to a rectangle fill via control template etc.

Answer 1

You might have noticed that the number of parameters that you can pass to Converter is just 1. You may pass an array of string or whatsoever, but I believe having all of your arguments in a single string would be easier to write and handle. For ex: "Empty=White|Filled=Black|Unknown=Gray"

Your converter should look like this:

public class SquareConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is string arg && parameter is string str)
        {
            string[] splits = str.Split("|"); // split by the delimiter
            var colorConverter = new ColorConverter(); // required to convert invariant string to color
            foreach (var kv in splits)
            {
                if(kv.StartsWith(arg, StringComparison.OrdinalIgnoreCase))
                {
                    var v = kv.Split("=")[1]; // get the value from key-value
                    var color = (Color)colorConverter.ConvertFromInvariantString(v); // convert string to color
                    var brush = new SolidColorBrush(color); // convert color to solid color brush
                    return brush;
                }
            }
        }

        return default;
    }

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

in your xaml

xmlns:c="clr-namespace:WpfApp.Converters"

<Window.Resources>
    <c:SquareConverter x:Key="SquareConverter"/>
</Window.Resources>

<Rectangle Fill="{Binding Path=Contents.Value,
                          Converter={StaticResource SquareConverter},
                          ConverterParameter='Empty=White|Filled=Black|Unknown=Gray'}"/>