Silverlight: Converter with multiple parameters

Sometimes it is necessary that you have a converter (interface IValueConverter) with multiple parameters. To reach this goal, you can use a DependencyProperty. That’s normally a very easy step, but I spend some extraordinary time with my converter becuase in my case the second parameter should be bindable

– So what was the problem?

I have tried to derive the Converter from UserControl – great mistake: You have to use FrameworkElement instead!

Usage:

   1: <Helpers:StatisticsConverter x:Key="StatisticsConverter" ViewModel="{Binding ElementName=LayoutRoot,Path=DataContext.Statistics}" />

   2:     

   3: <TextBlock Margin="0,0,10,0"

   4:    FontSize="9"  

   5:    x:Name="InfoSummeText" Text="{Binding Converter={StaticResource StatisticsConverter}, ConverterParameter=Summe}" >

   6: </TextBlock>

Converter:

   1: public class StatisticsConverter : FrameworkElement, IValueConverter

   2:    {

   3:  

   4:        #region IValueConverter Members

   5:  

   6:        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

   7:        {

   8:            var statisticsViewModel = (StatisticsViewModel)ViewModel;

   9:            var statistics = statisticsViewModel.GetAnzeigeKategorieStatistics(value as AnzeigeKategorie);

  10:            switch (parameter.ToString())

  11:            {

  12:                case "Summe":

  13:                    {

  14:                        return String.Format("{0:N2}", statistics.Summe) + " EUR";

  15:                    }

  16:                default:

  17:                    {

  18:                        throw new NotImplementedException(parameter as string);

  19:                    }

  20:            }

  21:        }

  22:  

  23:        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

  24:        {

  25:            return "";

  26:        }

  27:  

  28:        #endregion

  29:  

  30:        #region object ViewModel (DependencyProperty)

  31:  

  32:        public object ViewModel

  33:        {

  34:            get { return (object)GetValue(ViewModelProperty); }

  35:            set { SetValue(ViewModelProperty, value); }

  36:        }

  37:  

  38:        public static readonly DependencyProperty ViewModelProperty =

  39:            DependencyProperty.Register(

  40:                "ViewModel",

  41:                typeof(object),

  42:                typeof(StatisticsConverter),

  43:                new PropertyMetadata(null, null));

  44:  

  45:  

  46:        #endregion ViewModel (DependencyProperty)

  47:    }