Question

I saw in this post a solution that fits exactly my needs https://stackoverflow.com/a/8858815/1462911.

But I don’t really know how to properly implement it.

I have for now a PositionConverter which converts coordinates in Strings but i’d like to pass through its parameter the ActualWidth of its Parent (a Canvas).

Does my ConverterHelper have to implement IValueConverter and DependencyObject or just DependencyObject?

I’m a bit lost….

Answer 1

What you need is best accomplished through an IMultiValueConverter and a MultiBinding:

public class PositionConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        var scale = (double)values[0]; // this is your [0, 1] double
        var max = (double)values[1]; // this is the ActualWidth
        return scale * max;
    }
}

The binding would look like:

<Element.Property>
    <MultiBinding Converter="{StaticResource myConverter}">
        <Binding Path="path_to_the_original_double" />
        <Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorLevel=1}"
                 Path="ActualWidth" />
    </MultiBinding>
</Element.Property>