Converter cannot be applied to a property that expects the type System.Windows.Data.IValueConverter

Question

I am having a problem in my WPF app that I do not quite understand. I am trying to bind a fill to a different color depending on the value of a certain property.

Here are the snippets involved:

public class GeoLocations
{

    private static ObservableCollection<Bus> _locations = new ObservableCollection<Bus>();
    public static ObservableCollection<Bus> locations
    {
        get { return _locations; }
        set 
        { 
            _locations = value;      
        }
    }
.
.
.
}
public class Bus : INotifyPropertyChanged
{
    private double _VSAI;
    public double VSAI
    {
        get
        {
            return _VSAI;
        }
        set
        {
            _VSAI = value;
            OnPropertyChanged(new PropertyChangedEventArgs("VSAI"));
        }
    }
public class VsaiToColorConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        double vsai = (double)value;

        if (vsai < App.Settings.medVSAI)
            return Brushes.Green;

        if (vsai >= App.Settings.medVSAI && vsai <= App.Settings.maxVSAI)
            return Brushes.Yellow;


        if (vsai > App.Settings.maxVSAI)
            return Brushes.Red;

        return Brushes.Transparent;
    }

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

Then in my xaml I have the following:

in my resources I have

<local:GeoLocations x:Key="geolocs"/>

and then I have a map

<ig:GeographicProportionalSymbolSeries x:Name="ProportionalSeries"
                                                       LongitudeMemberPath="Longitude"
                                                       LatitudeMemberPath="Latitude"
                                                       ItemsSource="{Binding Source={StaticResource geolocs}, Path=locations}"
                                                       >
                    <!-- custom marker template for GeographicProportionalSymbolSeries -->
                    <ig:GeographicProportionalSymbolSeries.MarkerTemplate>
                        <DataTemplate>
                            <Ellipse x:Name="RootElement" Width="10" Height="10" 
                                     Stroke="DarkGray"
                                     Opacity=".8"
                                     StrokeThickness="0.5" 
                                     Fill="{Binding Path=Item.VSAI, Converter={StaticResource VSAIConverter}}">
                          </Ellipse>
                        </DataTemplate>
                    </ig:GeographicProportionalSymbolSeries.MarkerTemplate>

But the error I'm getting is on the FILL=..... above. I'm hoping this is an easy fix. I'm just a little too new still to understand how to fix this and what this error means.

Answer 1

Your converter needs to implement the IValueConverter interface. You've implemented the two methods but you omitted the IValueConverter interface so as far as the CLR is concerned, you just have a class that happens to have the same methods as IValueConverter but isn't actually implementing it.

public class VsaiToColorConverter : IValueConverter

You generally want to handle null value cases as well

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{  
    if(value == null) return Brushes.Transparent; //or null
    double vsai = (double)value;
    //..
}