How to customize the legend Icon based on series appearance in WPF Chart

    <Grid>
        <Grid.DataContext>
            <local:ViewModel></local:ViewModel>
        </Grid.DataContext>
        <chart:SfChart Margin="10">
            <chart:SfChart.Legend>
                <chart:ChartLegend></chart:ChartLegend>
            </chart:SfChart.Legend>
            <chart:SfChart.PrimaryAxis>
                <chart:CategoryAxis  LabelFormat="MMM/dd"></chart:CategoryAxis>
            </chart:SfChart.PrimaryAxis>
            <chart:SfChart.SecondaryAxis>
                <chart:NumericalAxis ></chart:NumericalAxis>
            </chart:SfChart.SecondaryAxis>
            <chart:FastLineSeries Label="Series 1" StrokeDashArray="1,1" ItemsSource="{Binding DataCollection}" XBindingPath="Date" YBindingPath="Value">
                <chart:FastLineSeries.LegendIconTemplate>
                    <DataTemplate >
                        <Polyline Points="0,8,25,8" Stroke="{Binding Interior}" StrokeThickness="{Binding StrokeThickness}" StrokeDashArray="1,1"/>
                    </DataTemplate>
                </chart:FastLineSeries.LegendIconTemplate>
            </chart:FastLineSeries>
        </chart:SfChart>
    </Grid>
 

public class Data
    {
        public Data(DateTime date, double value)
        {
            Date = date;
            Value = value;
        }
 
        public DateTime Date
        {
            get;
            set;
        }
 
        public double Value
        {
            get;
            set;
        }
    }
 
    public class ViewModel
    {
        public int DataCount = 100;
 
        private Random randomNumber;
 
        public ObservableCollection<Data> DataCollection { get; set; }
 
        public ViewModel()
        {
            randomNumber = new Random();
            DataCollection = GenerateData();
        }
 
        public ObservableCollection<Data> GenerateData()
        {
            ObservableCollection<Data> datas = new ObservableCollection<Data>();
 
            DateTime date = new DateTime(2000, 1, 1);
            double value = 100;
            for (int i = 0; i < this.DataCount; i++)
            {
                datas.Add(new Data(date, value));
                date = date.Add(TimeSpan.FromDays(5));
 
                if (randomNumber.NextDouble() > .5)
                {
                    value += randomNumber.NextDouble();
                }
                else
                {
                    value -= randomNumber.NextDouble();
                }
            }
 
            return datas;
        }
    }