Silverlight Multi-Binding

using System;
using System.Globalization;
using System.Windows.Data;

namespace slMultiBinding
{
    public class Bindings2ConcatString : IMultiValueConverter// IMyMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            string ret = "";
            foreach (Object param in values)
            {
                if (param != null)
                {
                    ret += param.ToString();
                }
            }
            return ret;
        }

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



    public class Num2Pow : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Math.Pow(System.Convert.ToDouble(value), System.Convert.ToDouble(parameter));
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return null;
        }
    }

    public class Nums2Sum : IMultiValueConverter
    {

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            //return 0;
            //if (values == null || (values.AsQueryable().Any(v => v == null || v == DependencyProperty.UnsetValue)))
            //{
            //    return 0;
            //}

            double ret = 0;
            foreach (Object param in values)
            {
                if (param != null)
                {
                    ret += System.Convert.ToDouble(param);
                }
            }
            return ret;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            return null;
        }
    }

}