I'm trying to plot a “stepline” chart where AxisX is a DateTime and some points are nulls.
As I didn't find any specific series (I hope you'll address soon), I use LineSeriesDefinizion doubling data point (see code) but:
- null value are treated as 0 (wrong since 0 means 0 value while null means missing value)
- where first value is null, the control throws a NullReferenceException

        public MainWindow()

        {

            InitializeComponent();

            ConfigureChart();

        }

        private void ConfigureChart()

        {

            LineSeriesDefinition lineSeries = new LineSeriesDefinition();

            lineSeries.ShowItemLabels = false;

            lineSeries.ShowPointMarks = false;

            SeriesMapping actualMapping = new SeriesMapping();

            actualMapping.SeriesDefinition = lineSeries;

            actualMapping.LegendLabel = "Data";

            actualMapping.ItemMappings.Add(new ItemMapping("Day", DataPointMember.XValue));

            actualMapping.ItemMappings.Add(new ItemMapping("Value", DataPointMember.YValue));

            radChart.SeriesMappings.Add(actualMapping);

            radChart.DefaultView.ChartArea.AxisX.DefaultLabelFormat = "#VAL{dd-MM-yy}";

            radChart.DefaultView.ChartArea.AxisX.LabelRotationAngle = 45;

            radChart.DefaultView.ChartArea.AxisX.IsDateTime = true;

            radChart.ItemsSource = MyData.GetData();

        }

    }

    class MyData

    {

        public DateTime Day { get; set; }

        public double? Value { get; set; }

        public static List<MyData> GetData()

        {

            DateTime today = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day);

            List<MyData> list = new List<MyData>();

            list.Add(new MyData() { Day = today, Value = null });

            list.Add(new MyData() { Day = today.AddDays(1), Value = 1 });

            list.Add(new MyData() { Day = today.AddDays(1), Value = 2 });

            list.Add(new MyData() { Day = today.AddDays(2), Value = 2 });

            list.Add(new MyData() { Day = today.AddDays(2), Value = 1.5 });

            list.Add(new MyData() { Day = today.AddDays(3), Value = 1.5 });

            return list;

        }

    }

Sincerely
Ivano