StringFormat is ignored

Question

This is my binding (shortened, Command-Property is also bound)

Answer 1

use Binding Converter:

public class CommandParamConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is string)
        {
            return string.Format("Key {0}", value);
        }
        return value;
    }

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

Add it to Windows\UserControl resource:

Refer it in Menu CommandParameter binding: