Currently, VisualStudio2012DarkTheme has a white background in order to be able to read the labels. This change was done when addressing this item:

https://feedback.telerik.com/winforms/1535458-radchartview-the-axis-label-are-difficult-to-read-in-visualstudio2012darktheme 

However, it is inconsistent a dark theme to have a white background color. The design should be improved to achieve consistent look and feel.

Public Class RadForm2
    Public Sub New()
        InitializeComponent()

        AddHandler Me.RadChartView1.CreateRenderer, AddressOf radChartView1_CreateRenderer

        Me.RadChartView1.ShowSmartLabels = True
        Me.RadChartView1.ShowPanZoom = True

        Dim barSeries As New BarSeries()
        Dim barSeries1 As New BarSeries()
        Dim barSeries2 As New BarSeries()
        Dim rand As New Random()
        barSeries.DataPoints.Add(New CategoricalDataPoint(101, 0))
        barSeries1.DataPoints.Add(New CategoricalDataPoint(101, 0))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(101, 0))
        For i As Integer = 1 To 9
            barSeries.DataPoints.Add(New CategoricalDataPoint(rand.[Next](100), i))
            barSeries1.DataPoints.Add(New CategoricalDataPoint(rand.[Next](100), i))
            barSeries2.DataPoints.Add(New CategoricalDataPoint(rand.[Next](100), i))
        Next

        barSeries.ShowLabels = True
        barSeries.DrawLinesToLabels = True
        barSeries1.ShowLabels = True
        barSeries1.DrawLinesToLabels = True
        barSeries2.ShowLabels = True
        barSeries2.DrawLinesToLabels = True

        Me.RadChartView1.Series.Add(barSeries)
        Me.RadChartView1.Series.Add(barSeries1)
        Me.RadChartView1.Series.Add(barSeries2)
    End Sub

    Private Sub radChartView1_CreateRenderer(sender As Object, e As ChartViewCreateRendererEventArgs)
        'e.Renderer = New CustomCartesianRenderer(TryCast(e.Area, CartesianArea))
    End Sub
End Class


Workaround: Create a custom renderer
Public Class CustomCartesianRenderer
    Inherits CartesianRenderer
    Public Sub New(area As CartesianArea)
        MyBase.New(area)
    End Sub

    Protected Overrides Sub Initialize()
        MyBase.Initialize()

        For i As Integer = 0 To Me.DrawParts.Count - 1
            Dim labelPart As BarLabelElementDrawPart = TryCast(Me.DrawParts(i), BarLabelElementDrawPart)
            If labelPart IsNot Nothing Then
                Me.DrawParts(i) = New CustomBarLabelElementDrawPart(DirectCast(labelPart.Element, BarSeries), Me)
            End If
        Next
    End Sub
End Class

Public Class CustomBarLabelElementDrawPart
    Inherits BarLabelElementDrawPart
    Public Sub New(owner As ChartSeries, renderer As IChartRenderer)
        MyBase.New(owner, renderer)
    End Sub

    Public Overrides Sub Draw()
        Dim graphics As Graphics = TryCast(Me.Renderer.Surface, Graphics)
        Dim cartesianSeries As CartesianSeries = TryCast(Me.Element, CartesianSeries)
        If cartesianSeries IsNot Nothing Then
            Dim area As CartesianArea = DirectCast(cartesianSeries.[GetType]().GetField("area", BindingFlags.Instance Or BindingFlags.NonPublic).GetValue(cartesianSeries), CartesianArea)
            Dim clipRect As RectangleF = DirectCast(area.[GetType]().GetMethod("GetCartesianClipRect", BindingFlags.Instance Or BindingFlags.NonPublic).Invoke(area, New Object() {}), RectangleF)

            graphics.SetClip(clipRect)
        End If

        MyBase.Draw()

        graphics.ResetClip()
    End Sub

    Protected Overrides Function GetLineStart(label As LabelElement, point As DataPointElement, isSmartLabel As Boolean) As PointF
        Dim lineStart As PointF = MyBase.GetLineStart(label, point, isSmartLabel)

        Dim x As Single = CSng(TryCast(Me.Element.View, IChartView).PlotOriginX)
        Dim y As Single = CSng(TryCast(Me.Element.View, IChartView).PlotOriginY)

        lineStart.X += x
        lineStart.Y += y

        Return lineStart
    End Function

    Protected Overrides Function GetLineEnd(label As LabelElement, point As DataPointElement, isSmartLabel As Boolean) As PointF
        Dim lineEnd As PointF = MyBase.GetLineEnd(label, point, isSmartLabel)

        If Not isSmartLabel Then
            Dim x As Single = CSng(TryCast(Me.Element.View, IChartView).PlotOriginX)
            Dim y As Single = CSng(TryCast(Me.Element.View, IChartView).PlotOriginY)
            lineEnd.X += x
            lineEnd.Y += y
        End If

        Return lineEnd
    End Function
End Class

To reproduce:
- Set the position like this:
this.radChartView1.ChartElement.LegendElement.Alignment = ContentAlignment.TopCenter;

- Export the chart to an image, the position is not the same as in the application.

Workaround:
- Set the position manually:

this.radChartView1.ChartElement.LegendPosition = LegendPosition.Float;
this.radChartView1.ChartElement.LegendOffset = new Point(400, 0);

How to reproduce:

Public Class Form1

    Sub New()

        InitializeComponent()

        Me.SetupLineSeries()

    End Sub

    Private Sub SetupLineSeries()
        Dim splitContainer = New RadSplitContainer()
        splitContainer.SplitPanels.Add(New SplitPanel())
        splitContainer.SplitPanels.Add(New SplitPanel())
        splitContainer.SplitPanels(0).Controls.Add(Me.RadChartView1)
        Me.RadChartView1.Dock = DockStyle.Fill

        splitContainer.Orientation = Orientation.Horizontal
        splitContainer.Parent = Me
        splitContainer.Dock = DockStyle.Fill


        Dim lineSeries As New Telerik.WinControls.UI.LineSeries("2014")
        lineSeries.LegendTitle = "2014"
        lineSeries.ShowLabels = True

        lineSeries.DataPoints.Add(New CategoricalDataPoint(8000, "Jan"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8700, "Feb"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8500, "Mar"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8900, "Apr"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8400, "May"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8300, "Jun"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8600, "Jul"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8800, "Aug"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8400, "Sep"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8300, "Oct"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8500, "Nov"))
        lineSeries.DataPoints.Add(New CategoricalDataPoint(8100, "Dec"))

        Me.RadChartView1.Series.Add(lineSeries)
        Dim lineSeries2 As New Telerik.WinControls.UI.LineSeries("2015")
        lineSeries2.LegendTitle = "2015"
        lineSeries2.ShowLabels = True

        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5800, "Jan"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5900, "Feb"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5700, "Mar"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5500, "Apr"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5300, "May"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5600, "Jun"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5800, "Jul"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5800, "Aug"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(5900, "Sep"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(6100, "Oct"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(7900, "Nov"))
        lineSeries2.DataPoints.Add(New CategoricalDataPoint(7600, "Dec"))
        Me.RadChartView1.Series.Add(lineSeries2)

        Me.RadChartView1.ShowSmartLabels = True
        Me.RadChartView1.ShowTitle = True
        Me.RadChartView1.ShowLegend = True
        Me.RadChartView1.LegendTitle = "Legend"

        Dim verticalAxis As LinearAxis = RadChartView1.Axes.[Get](Of LinearAxis)(1)
        verticalAxis.Minimum = 4000
        verticalAxis.Maximum = 20000
        verticalAxis.MajorStep = 4000

        Me.RadChartView1.ShowPanZoom = True
    End Sub

End Class

How to reproduce: 
Public Class Form1

    Sub New()

        InitializeComponent()

        Dim barSeries As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries.Name = "Q1"
        barSeries.LegendTitle = "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "Leg

        barSeries.DataPoints.Add(New CategoricalDataPoint(177, "Harley"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(128, "White"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(143, "Smith"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(111, "Jones"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(118, "Marshall"))

        Me.RadChartView1.Series.Add(barSeries)
        Dim barSeries2 As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries2.Name = "Q2"
        barSeries2.LegendTitle = "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "Le

        barSeries2.DataPoints.Add(New CategoricalDataPoint(153, "Harley"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(141, "White"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(130, "Smith"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(88, "Jones"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(109, "Marshall"))
        Me.RadChartView1.Series.Add(barSeries2)

        Me.RadChartView1.ShowTitle = True
        Me.RadChartView1.ShowLegend = True
        Me.RadChartView1.LegendTitle = "Legend"

        Me.RadChartView1.Size = New Size(500, 150)
        Me.RadChartView1.ShowPanZoom = True

        'Me.SetupLineSeries()

    End Sub

    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        Dim filePath As String = "..\..\exprotedChart2.png"
        Me.RadChartView1.ExportToImage(filePath, New Size(1000, 800), System.Drawing.Imaging.ImageFormat.Png)

    End Sub
End Class

Workaround: increase the size of the chart
Public Class Form1

    Sub New()

        InitializeComponent()

        Dim barSeries As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries.Name = "Q1"
        barSeries.LegendTitle = "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1"

        barSeries.DataPoints.Add(New CategoricalDataPoint(177, "Harley"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(128, "White"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(143, "Smith"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(111, "Jones"))
        barSeries.DataPoints.Add(New CategoricalDataPoint(118, "Marshall"))

        Me.RadChartView1.Series.Add(barSeries)
        Dim barSeries2 As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
        barSeries2.Name = "Q2"
        barSeries2.LegendTitle = "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1" + vbCrLf + "LegendTitle1"

        barSeries2.DataPoints.Add(New CategoricalDataPoint(153, "Harley"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(141, "White"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(130, "Smith"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(88, "Jones"))
        barSeries2.DataPoints.Add(New CategoricalDataPoint(109, "Marshall"))
        Me.RadChartView1.Series.Add(barSeries2)

        Me.RadChartView1.ShowTitle = True
        Me.RadChartView1.ShowLegend = True
        Me.RadChartView1.LegendTitle = "Legend"

        Me.RadChartView1.Size = New Size(500, 150)
        Me.RadChartView1.ShowPanZoom = True

        'Me.SetupLineSeries()

    End Sub

    Dim size As Size
    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        AddHandler Me.RadChartView1.SizeChanged, AddressOf RadChartView1_SizeChanged
        size = Me.RadChartView1.Size
        Me.RadChartView1.Size = New Size(1000, 800)

    End Sub

    Private Sub RadChartView1_SizeChanged(sender As Object, e As EventArgs)
        RemoveHandler Me.RadChartView1.SizeChanged, AddressOf RadChartView1_SizeChanged

        Dim filePath As String = "..\..\exprotedChart2.png"
        Me.RadChartView1.ExportToImage(filePath, Me.RadChartView1.Size, System.Drawing.Imaging.ImageFormat.Png)
        Me.RadChartView1.Size = size
    End Sub
End Class

Improve performance, when calculating the positions of Smart Labels.

To reproduce:
- Add polar series and selection controller


Workaround:

private void RadChartView1_CreateRenderer(object sender, ChartViewCreateRendererEventArgs e)
{
    e.Renderer = new MyPolarRenderer(e.Area as PolarArea);
}

class MyPolarRenderer : PolarRenderer
{
    public MyPolarRenderer(PolarArea area) : base(area)
    { }

    public override DataPoint HitTest(int x, int y)
    {
        for (int i = 0; i < this.DrawParts.Count; i++)
        {
            DataPoint dataPoint = this.DrawParts[i].HitTest(new Point(x, y));
            if (dataPoint != null)
            {
                return dataPoint;
            }
        }

        return base.HitTest(x, y);
    }
    protected override void Initialize()
    {
        base.Initialize();
        for (int i = 0; i < this.DrawParts.Count; i++)
        {
            PolarPointSeriesDrawPart linePart = this.DrawParts[i] as PolarPointSeriesDrawPart;
            if (linePart != null)
            {
                this.DrawParts[i] = new MyDrawpart((PolarPointSeries)linePart.Element, this);
            }
        }
    }

}
class MyDrawpart : PolarPointSeriesDrawPart
{
    public MyDrawpart(PolarPointSeries series, IChartRenderer renderer) : base(series, renderer)
    { }
    public override DataPoint HitTest(Point location)
    {
        if (this.Element.PointSize.Width == 0 || this.Element.PointSize.Height == 0)
        {
            return null;
        }

        for (int i = 0; i < this.Element.DataPoints.Count; i++)
        {
            RadRect slot = this.Element.DataPoints[i].LayoutSlot;
            float pointHalfWidth = this.Element.PointSize.Width / 2;
            float pointHalfHeight = this.Element.PointSize.Height / 2;

            RectangleF dataPointBounds = new RectangleF((float)(slot.X - pointHalfWidth), (float)(slot.Y - pointHalfHeight), this.Element.PointSize.Width, this.Element.PointSize.Height);

            if (dataPointBounds.Contains(location.X, location.Y))
            {
                return this.Element.DataPoints[i];
            }
        }

        return base.HitTest(location);
    }
}

Workaround: use a custom ChartPanZoomController

public class MyChartPanZoomController : ChartPanZoomController
    {
        protected override ActionResult OnMouseWheel(MouseEventArgs e)
        {
            if (!(this.Area is CartesianArea))
            {
                return base.OnMouseWheel(e);
            }

            if ((Control.ModifierKeys & Keys.Control) == Keys.Control)
            {
                IChartView chartView = this.Area.View;

                double zoomWidth = chartView.ZoomWidth;

                if (this.PanZoomMode == ChartPanZoomMode.Horizontal || this.PanZoomMode == ChartPanZoomMode.Both)
                {
                    zoomWidth += ((double)e.Delta / 1200d);
                }

                double zoomHeight = chartView.ZoomHeight;

                if (this.PanZoomMode == ChartPanZoomMode.Vertical || this.PanZoomMode == ChartPanZoomMode.Both)
                {
                    zoomHeight += ((double)e.Delta / 1200d);
                }

                zoomWidth = this.ClampValue(zoomWidth, 1d, 100d);
                zoomHeight = this.ClampValue(zoomHeight, 1d, 100d);

                double virtualHorizontalPosition = e.X - this.Area.AreaModel.LayoutSlot.X - chartView.PlotOriginX;
                double plotAreaVirtualWidth = this.Area.AreaModel.LayoutSlot.Width * chartView.ZoomWidth;
                double relativeHorizontalPosition = virtualHorizontalPosition / plotAreaVirtualWidth;
                double newPlotAreaVirtualWidth = this.Area.AreaModel.LayoutSlot.Width * zoomWidth;
                double newPanOffsetX = (newPlotAreaVirtualWidth * relativeHorizontalPosition) - (e.X - this.Area.AreaModel.LayoutSlot.X);
                newPanOffsetX = this.ClampValue(newPanOffsetX, 0, this.Area.AreaModel.LayoutSlot.Width * (zoomWidth - 1d));

                double virtualVerticalPosition = e.Y - this.Area.AreaModel.LayoutSlot.Y - chartView.PlotOriginY;
                double plotAreaVirtualHeight = this.Area.AreaModel.LayoutSlot.Height * chartView.ZoomHeight;
                double relativeVerticalPosition = virtualVerticalPosition / plotAreaVirtualHeight;
                double newPlotAreaVirtualHeight = this.Area.AreaModel.LayoutSlot.Height * zoomHeight;
                double newPanOffsetY = (newPlotAreaVirtualHeight * relativeVerticalPosition) - (e.Y - this.Area.AreaModel.LayoutSlot.Y);
                newPanOffsetY = this.ClampValue(newPanOffsetY, 0, this.Area.AreaModel.LayoutSlot.Height * (zoomHeight - 1d));

                this.Area.View.Zoom(zoomWidth, zoomHeight);
                this.Area.View.Pan(-newPanOffsetX, -newPanOffsetY);
            }

            return Controller.Empty;
        }

        private double ClampValue(double value, double minValue, double maxValue)
        {
            return Math.Max(minValue, Math.Min(value, maxValue));
        }
    }

To reproduce:

public RadForm1()
{
    InitializeComponent();
    Random rand = new Random(); 
    
    LineSeries lineSeria = new LineSeries();
    lineSeria.ValueMember = "WorkingHours";
    lineSeria.CategoryMember = "Date";
    lineSeria.ShowLabels = true;
    lineSeria.PointSize = new System.Drawing.SizeF(10, 10);
    lineSeria.BackColor = Color.Red;
    LinearAxis verticalAxis2 = new LinearAxis();
    verticalAxis2.AxisType = AxisType.Second;
    verticalAxis2.HorizontalLocation = AxisHorizontalLocation.Right ;
    lineSeria.VerticalAxis = verticalAxis2;
    DataTable table = new DataTable();
    table.Columns.Add("Value", typeof(double));
    table.Columns.Add("Name", typeof(string));
    table.Rows.Add(rand.Next(1, 20), "John");
    table.Rows.Add(rand.Next(1, 20), "Adam");
    table.Rows.Add(rand.Next(1, 20), "Peter");
    table.Rows.Add(rand.Next(1, 20), "Sam");
    table.Rows.Add(rand.Next(1, 20), "Paul");
    lineSeria.ValueMember = "Value";
    lineSeria.CategoryMember = "Name";
    lineSeria.DataSource = table;

    BarSeries barSeria = new BarSeries();
   
    barSeria.ValueMember = "Finished";
    barSeria.CategoryMember = "Date";
    barSeria.ShowLabels = true;
    barSeria.BackColor = Color.Aqua;
    LinearAxis verticalAxis1 = new LinearAxis();
    verticalAxis1.AxisType = AxisType.Second;
    verticalAxis1.HorizontalLocation = AxisHorizontalLocation.Left;
    barSeria.VerticalAxis = verticalAxis1;

    table = new DataTable();
    table.Columns.Add("Value", typeof(double));
    table.Columns.Add("Name", typeof(string));
    table.Rows.Add(rand.Next(1, 20), "John");
    table.Rows.Add(rand.Next(1, 20), "Adam");
    table.Rows.Add(rand.Next(1, 20), "Peter");
    table.Rows.Add(rand.Next(1, 20), "Sam");
    table.Rows.Add(rand.Next(1, 20), "Paul");
    barSeria.ValueMember = "Value";
    barSeria.CategoryMember = "Name";
    barSeria.DataSource = table;

    this.radChartView1.ChartElement.View.Series.Add(lineSeria);
    this.radChartView1.ChartElement.View.Series.Add(barSeria);
    this.radChartView1.ChartElement.Margin = new System.Windows.Forms.Padding(10);
    (this.radChartView1.ChartElement.View.Axes[0] as CategoricalAxis).LabelFitMode =
        Telerik.Charting.AxisLabelFitMode.MultiLine; 
     
    SmartLabelsController c = new SmartLabelsController();

    this.radChartView1.ChartElement.View.Controllers.Add(c);
}

Workaround: change the strategy: 
SmartLabelsController c = new SmartLabelsController();
c.Strategy = new FourPositionsLabelsStrategy();
this.radChartView1.ChartElement.View.Controllers.Add(c);

Workaround:

 Sub New()

     InitializeComponent()

     AddHandler Me.RadChartView1.CreateRenderer, AddressOf CreateRenderer
     
     AddHandler Me.RadChartView1.LabelFormatting, AddressOf LabelFormatting 
     Dim barSeries As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
     barSeries.ShowLabels = True

     barSeries.DataPoints.Add(New CategoricalDataPoint(177, "Harley"))
     barSeries.DataPoints.Add(New CategoricalDataPoint(128, "White"))
     barSeries.DataPoints.Add(New CategoricalDataPoint(143, "Smith"))
     barSeries.DataPoints.Add(New CategoricalDataPoint(111, "Jones"))
     barSeries.DataPoints.Add(New CategoricalDataPoint(118, "Marshall"))
     Me.RadChartView1.Series.Add(barSeries)
     Dim barSeries2 As New Telerik.WinControls.UI.BarSeries("Performance", "RepresentativeName")
     barSeries2.ShowLabels = True
     barSeries2.DataPoints.Add(New CategoricalDataPoint(153, "Harley"))
     barSeries2.DataPoints.Add(New CategoricalDataPoint(141, "White"))
     barSeries2.DataPoints.Add(New CategoricalDataPoint(130, "Smith"))
     barSeries2.DataPoints.Add(New CategoricalDataPoint(88, "Jones"))
     barSeries2.DataPoints.Add(New CategoricalDataPoint(109, "Marshall"))
     Me.RadChartView1.Series.Add(barSeries2)

 End Sub

 Private Sub LabelFormatting(sender As Object, e As Telerik.WinControls.UI.ChartViewLabelFormattingEventArgs)
     Dim dataPoint As CategoricalDataPoint = TryCast(e.LabelElement.DataPoint, CategoricalDataPoint)
     e.LabelElement.Text = "Value: " & Environment.NewLine & dataPoint.Value
     e.LabelElement.BackColor = Color.Yellow 
 End Sub

 Private Sub CreateRenderer(sender As Object, e As ChartViewCreateRendererEventArgs)
     e.Renderer = New CustomCartesianRenderer(TryCast(e.Area, CartesianArea))
 End Sub

 Public Class CustomCartesianRenderer
 Inherits CartesianRenderer

     Public Sub New(area As CartesianArea)
         MyBase.New(area)

     End Sub

     Protected Overrides Sub Initialize()
         MyBase.Initialize()

         For i As Integer = 0 To Me.DrawParts.Count - 1
             Dim labelPart As BarLabelElementDrawPart = TryCast(Me.DrawParts(i), BarLabelElementDrawPart)
             If labelPart IsNot Nothing Then
                 Me.DrawParts(i) = New CustomLabelElementDrawPart(DirectCast(labelPart.Element, BarSeries), Me)
             End If
         Next
     End Sub
 End Class

 Public Class CustomLabelElementDrawPart
 Inherits BarLabelElementDrawPart
     Public Sub New(owner As ChartSeries, renderer As IChartRenderer)
         MyBase.New(owner, renderer)
     End Sub

     Public Overrides Sub Draw()
         For Each dataPointElement As DataPointElement In Me.Element.Children
             For Each label As LabelElement In dataPointElement.Children
                 label.ForeColor = Color.Transparent
             Next
         Next

         MyBase.Draw()
         Dim graphics As Graphics = TryCast(Me.Renderer.Surface, Graphics)
         Dim radGraphics As New RadGdiGraphics(graphics)
         Dim slot As RadRect
         Dim rect As Rectangle
         Dim stringFormat As New StringFormat()
         stringFormat.Alignment = StringAlignment.Center
         stringFormat.LineAlignment = StringAlignment.Center

         For Each dataPointElement As DataPointElement In Me.Element.Children
             For Each label As LabelElement In dataPointElement.Children
                 label.ForeColor = Color.Transparent
                 slot = label.GetLayoutSlot()
                 slot = AdjustLayoutSlot(slot, label.DataPointElement)
                 rect = ChartRenderer.ToRectangle(slot)
                 Using brush As Brush = New SolidBrush(Color.Red)
                     Dim drawLocation As New PointF()
                     drawLocation.X = rect.X + label.Padding.Left
                     drawLocation.Y = rect.Y + label.Padding.Top

                     graphics.DrawString(label.Text, label.Font, brush, rect, stringFormat)
                 End Using
             Next
         Next
     End Sub
 End Class

Good day,

My requierment is to have a RadChartView with a LineSeries and a RangeSeries.  I add CategoricalDataPoint objects manually to the LineSeries and I manually add RangeDataPoint objects to the RangeSeries. 

When I encounter NULL valued datapoints, for the LineSeries, I do the following.  The NULL valued datapoints appear as gaps in the chart as expected.

Dim value As Nullable(Of Double)
Dim serControl  As  LineSeries

serControl = New LineSeries()
chart.Series.Add(serControl)
value = IIf(IsDBNull(dr(data.ControlParameter.ID.ToString())), New Nullable(Of Double), dr(data.ControlParameter.ID.ToString()))
serControl.DataPoints.Add(New Telerik.Charting.CategoricalDataPoint(value))

However the RangeSeries do not handle the NULL valued datapoints the same.  I get the following error:  Nullable object must have a value.

Dim LowerBound, UpperBound As Nullable(Of Double)
Dim serRange  As  RangeSeries

serRange = New RangeSeries()
chart.Series.Add(serRange)
LowerBound = IIf(IsDBNull(dr("Lowerbound"), New Nullable(Of Double), dr("LowerBound"))
UpperBound = IIf(IsDBNull(dr("Upperbound"), New Nullable(Of Double), dr("UpperBound"))
serRange.DataPoints.Add(New Telerik.Charting.RangeDataPoint(UpperBound, LowerBound))

I need to be able to show gaps, not zero's in a RangeSeries when there are NULL values.

How can I do this?

How to reproduce:
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.radChartView1.ShowLegend = true;

        LineSeries lineSeries = new LineSeries();
        lineSeries.DataPoints.Add(new CategoricalDataPoint(20, "Jan"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(22, "Apr"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(12, "Jul"));
        lineSeries.DataPoints.Add(new CategoricalDataPoint(19, "Oct"));
        this.radChartView1.Series.Add(lineSeries);

        LineSeries lineSeries2 = new LineSeries();
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(18, "Jan"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(15, "Apr"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(17, "Jul"));
        lineSeries2.DataPoints.Add(new CategoricalDataPoint(22, "Oct"));
        this.radChartView1.Series.Add(lineSeries2);

        ChartPanZoomController panZoomController = new ChartPanZoomController();
        panZoomController.PanZoomMode = ChartPanZoomMode.Horizontal;
        radChartView1.Controllers.Add(panZoomController);
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        this.radChartView1.ExportToImage(@"..\..\image.png", this.radChartView1.Size, System.Drawing.Imaging.ImageFormat.Png);
    }
}

Workaround: use a custom export to image method
public void ExportChartToImage(string filePath, Size size, ImageFormat imageFormat)
{
    using (FileStream fs = new FileStream(filePath, FileMode.Create, FileAccess.Write))
    {
        if (!this.radChartView1.IsLoaded)
        {
            this.radChartView1.LoadElementTree();
        }

        Bitmap bmp = new Bitmap(size.Width, size.Height);
        Graphics graphics = Graphics.FromImage(bmp);
        graphics.Clear(Color.White);

        SizeF titleSize = graphics.MeasureString(this.radChartView1.Title, this.radChartView1.ChartElement.TitleElement.Font, this.Width);

        if (this.radChartView1.ChartElement.TitleElement.TextOrientation == Orientation.Vertical)
        {
            float swap = titleSize.Height;
            titleSize.Height = titleSize.Width;
            titleSize.Width = swap;
        }

        RadRect titleRect = new RadRect(0, 0, titleSize.Width, titleSize.Height);
        RadRect legendRect = new RadRect(0, 0, size.Width, size.Height);
        RadRect chartRect = legendRect;

        switch (this.radChartView1.ChartElement.TitlePosition)
        {
            case TitlePosition.Top:
            case TitlePosition.Bottom:
                titleRect.Width = size.Width;
                break;
            case TitlePosition.Right:
            case TitlePosition.Left:
                titleRect.Height = size.Height;
                break;
        }

        chartRect.X += this.radChartView1.View.Margin.Left;
        chartRect.Y += this.radChartView1.View.Margin.Top;
        chartRect.Width -= this.radChartView1.View.Margin.Horizontal;
        chartRect.Height -= this.radChartView1.View.Margin.Vertical;

        if (this.radChartView1.ShowTitle)
        {
            switch (this.radChartView1.ChartElement.TitlePosition)
            {
                case TitlePosition.Top:
                    legendRect.Y += titleRect.Height;
                    chartRect.Y += titleRect.Height;
                    legendRect.Height -= titleRect.Height;
                    chartRect.Height -= titleRect.Height;
                    break;
                case TitlePosition.Right:
                    titleRect.X = size.Width - this.radChartView1.ChartElement.TitleElement.Size.Width;
                    titleRect.Height = size.Height;
                    legendRect.Width -= titleRect.Width;
                    chartRect.Width -= titleRect.Width;
                    break;
                case TitlePosition.Bottom:
                    titleRect.Y = size.Height - this.radChartView1.ChartElement.TitleElement.Size.Height;
                    titleRect.Width = size.Width;
                    legendRect.Height -= titleRect.Height;
                    chartRect.Height -= titleRect.Height;
                    break;
                case TitlePosition.Left:
                    titleRect.Height = size.Height;
                    legendRect.X += titleRect.Width;
                    chartRect.X += titleRect.Width;
                    legendRect.Width -= titleRect.Width;
                    chartRect.Width -= titleRect.Width;
                    break;
            }
        }

        if (this.radChartView1.ShowLegend)
        {
            switch (this.radChartView1.ChartElement.LegendPosition)
            {
                case LegendPosition.Right:
                    if (this.radChartView1.ChartElement.TitlePosition == TitlePosition.Right)
                    {
                        legendRect.X = titleRect.X - this.radChartView1.ChartElement.LegendElement.Size.Width;
                    }
                    else
                    {
                        legendRect.X = size.Width - this.radChartView1.ChartElement.LegendElement.Size.Width;
                    }

                    legendRect.Width = this.radChartView1.ChartElement.LegendElement.Size.Width;
                    chartRect.Width -= this.radChartView1.View.Margin.Right;
                    break;
                case LegendPosition.Bottom:
                    if (this.radChartView1.ChartElement.TitlePosition == TitlePosition.Bottom)
                    {
                        legendRect.Y = titleRect.Y - this.radChartView1.ChartElement.LegendElement.Size.Height;
                    }
                    else
                    {
                        legendRect.Y = size.Height - this.radChartView1.ChartElement.LegendElement.Size.Height;
                    }

                    legendRect.Height = this.radChartView1.ChartElement.LegendElement.Size.Height;
                    chartRect.Height -= legendRect.Height;
                    break;
                case LegendPosition.Left:
                    legendRect.Width = this.radChartView1.ChartElement.LegendElement.Size.Width;
                    chartRect.X += legendRect.Width + this.radChartView1.View.Margin.Left;
                    chartRect.Width -= legendRect.Width + this.radChartView1.View.Margin.Left;
                    break;
                case LegendPosition.Top:
                    legendRect.Height = this.radChartView1.ChartElement.LegendElement.Size.Height;
                    chartRect.Y += legendRect.Height;
                    chartRect.Height -= legendRect.Height;
                    break;
                case LegendPosition.Float:
                    legendRect.Width = this.radChartView1.ChartElement.LegendElement.Size.Width;
                    legendRect.Height = this.radChartView1.ChartElement.LegendElement.Size.Height;
                    double xRatio = size.Width / this.Size.Width;
                    double yRatio = size.Height / this.Size.Height;
                    legendRect.X = (this.radChartView1.ChartElement.LegendOffset.X * xRatio) + ((this.radChartView1.ChartElement.TitlePosition == TitlePosition.Left) ? titleRect.Right : 0d);
                    legendRect.Y = (this.radChartView1.ChartElement.LegendOffset.Y * yRatio) + ((this.radChartView1.ChartElement.TitlePosition == TitlePosition.Top) ? titleRect.Bottom : 0f);
                    break;
            }
        }

        if (this.radChartView1.ShowLegend)
        {
            float xTransform = (float)legendRect.X - this.radChartView1.ChartElement.LegendElement.ControlBoundingRectangle.X + ((float)legendRect.Width - this.radChartView1.ChartElement.LegendElement.ControlBoundingRectangle.Width) / 2f;
            float yTransform = (float)legendRect.Y - this.radChartView1.ChartElement.LegendElement.ControlBoundingRectangle.Y + ((float)legendRect.Height - this.radChartView1.ChartElement.LegendElement.ControlBoundingRectangle.Height) / 2f;
            graphics.TranslateTransform(xTransform, yTransform);
            this.radChartView1.ChartElement.LegendElement.Paint(new RadGdiGraphics(graphics), this.radChartView1.ChartElement.LegendElement.ControlBoundingRectangle, 0f, new SizeF(1f, 1f), true);
            graphics.ResetTransform();
        }

        RadGdiGraphics radGraphics = new RadGdiGraphics(graphics);

        if (this.radChartView1.ShowTitle)
        {
            object[] miParams = new object[] { ChartRenderer.ToRectangleF(titleRect), titleSize, this.radChartView1.ChartElement.TitleElement.TextAlignment };
            radGraphics.DrawString(this.radChartView1.Title, (RectangleF)typeof(RadChartView).GetMethod("GetTitleDrawRectangle", BindingFlags.Instance | BindingFlags.NonPublic).Invoke(this.radChartView1, miParams), this.radChartView1.ChartElement.TitleElement.Font,
                this.radChartView1.ChartElement.TitleElement.ForeColor, this.radChartView1.ChartElement.TitleElement.TextParams.CreateStringFormat(), this.radChartView1.ChartElement.TitleElement.TextOrientation, this.radChartView1.ChartElement.TitleElement.FlipText);
        }

        this.radChartView1.View.Layout(chartRect);

        IChartRenderer renderer = (IChartRenderer)typeof(ChartArea).GetProperty("Renderer", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(this.radChartView1.Area);//
        renderer.Draw(graphics);

        if (imageFormat == ImageFormat.Emf ||
            imageFormat == ImageFormat.Wmf)
        {
            Metafile metafile = new Metafile(fs, graphics.GetHdc());
            using (Graphics g = Graphics.FromImage(metafile))
            {
                g.DrawImage(bmp, Point.Empty);
            }

            metafile.Dispose();
            graphics.ReleaseHdc();
        }
        else
        {
            bmp.Save(fs, imageFormat);
        }

        this.radChartView1.View.Layout();
    }

Use the attached project to reproduce.

Workaround:
Check for zero values.

Workaround:

CartesianRenderer renderer = null;

public RadForm1()
{
    InitializeComponent();
    this.radChartView1.CreateRenderer += new ChartViewCreateRendererEventHandler(radChartView1_CreateRenderer);
    LineSeries lineSeries = new LineSeries();
    lineSeries.LegendTitle = "Line 1";
    lineSeries.DataPoints.Add(new CategoricalDataPoint(20, "Jan"));
    lineSeries.DataPoints.Add(new CategoricalDataPoint(22, "Apr"));
    lineSeries.DataPoints.Add(new CategoricalDataPoint(12, "Jul"));
    lineSeries.DataPoints.Add(new CategoricalDataPoint(19, "Oct"));
    this.radChartView1.Series.Add(lineSeries);
    LineSeries lineSeries2 = new LineSeries();
    lineSeries2.LegendTitle = "Line 2";
    lineSeries2.DataPoints.Add(new CategoricalDataPoint(18, "Jan"));
    lineSeries2.DataPoints.Add(new CategoricalDataPoint(15, "Apr"));
    lineSeries2.DataPoints.Add(new CategoricalDataPoint(17, "Jul"));
    lineSeries2.DataPoints.Add(new CategoricalDataPoint(22, "Oct"));
    this.radChartView1.Series.Add(lineSeries2);
    this.radChartView1.ShowLegend = true;
    this.radChartView1.ChartElement.LegendPosition = LegendPosition.Float;
    this.radChartView1.ChartElement.LegendOffset = new Point(200, 95);

    CartesianArea area = this.radChartView1.GetArea<CartesianArea>();
    area.ShowGrid = true;
}

private void radChartView1_CreateRenderer(object sender, ChartViewCreateRendererEventArgs e)
{
    renderer = new CartesianRenderer(e.Area as CartesianArea);
    e.Renderer = renderer; 
}

private void radButton1_Click(object sender, EventArgs e)
{ 
    string filePath = @"..\..\..\exportedChart" + DateTime.Now.ToLongTimeString().Replace(":", "_") + ".png";
    using (MemoryStream stream = new MemoryStream())
    {
        ExportToImage(this.radChartView1, stream, new Size(1000 ,500), ImageFormat.Png, filePath);
    }
    Process.Start(filePath);
}

public void ExportToImage(RadChartView chart, Stream stream, Size size, ImageFormat imageFormat, string filePath)
{
    if (!this.IsLoaded)
    {
        this.LoadElementTree();
    }

    size = Telerik.WinControls.TelerikDpiHelper.ScaleSize(size, chart.ChartElement.DpiScaleFactor);

    Bitmap bmp = new Bitmap(size.Width, size.Height);
    Graphics graphics = Graphics.FromImage(bmp);
    graphics.Clear(Color.White);

    SizeF titleSize = graphics.MeasureString(chart.Title, chart.ChartElement.TitleElement.Font, this.Width);

    if (chart.ChartElement.TitleElement.TextOrientation == Orientation.Vertical)
    {
        float swap = titleSize.Height;
        titleSize.Height = titleSize.Width;
        titleSize.Width = swap;
    }

    RadRect titleRect = new RadRect(0, 0, titleSize.Width, titleSize.Height);
    RadRect legendRect = new RadRect(0, 0, size.Width, size.Height);
    RadRect chartRect = legendRect;

    switch (chart.ChartElement.TitlePosition)
    {
        case TitlePosition.Top:
        case TitlePosition.Bottom:
            titleRect.Width = size.Width;
            break;
        case TitlePosition.Right:
        case TitlePosition.Left:
            titleRect.Height = size.Height;
            break;
    }

    chartRect.X += chart.View.Margin.Left;
    chartRect.Y += chart.View.Margin.Top;
    chartRect.Width -= chart.View.Margin.Horizontal;
    chartRect.Height -= chart.View.Margin.Vertical;

    if (chart.ShowTitle)
    {
        switch (chart.ChartElement.TitlePosition)
        {
            case TitlePosition.Top:
                legendRect.Y += titleRect.Height;
                chartRect.Y += titleRect.Height;
                legendRect.Height -= titleRect.Height;
                chartRect.Height -= titleRect.Height;
                break;
            case TitlePosition.Right:
                titleRect.X = size.Width - chart.ChartElement.TitleElement.Size.Width;
                titleRect.Height = size.Height;
                legendRect.Width -= titleRect.Width;
                chartRect.Width -= titleRect.Width;
                break;
            case TitlePosition.Bottom:
                titleRect.Y = size.Height - chart.ChartElement.TitleElement.Size.Height;
                titleRect.Width = size.Width;
                legendRect.Height -= titleRect.Height;
                chartRect.Height -= titleRect.Height;
                break;
            case TitlePosition.Left:
                titleRect.Height = size.Height;
                legendRect.X += titleRect.Width;
                chartRect.X += titleRect.Width;
                legendRect.Width -= titleRect.Width;
                chartRect.Width -= titleRect.Width;
                break;
        }
    }
    chart.View.Layout(chartRect);
    renderer.Draw(graphics);
    if (chart.ShowLegend)
    {
        switch (chart.ChartElement.LegendPosition)
        {
            case LegendPosition.Right:
                if (chart.ChartElement.TitlePosition == TitlePosition.Right)
                {
                    legendRect.X = titleRect.X - chart.ChartElement.LegendElement.Size.Width;
                }
                else
                {
                    legendRect.X = size.Width - chart.ChartElement.LegendElement.Size.Width;
                }

                legendRect.Width = chart.ChartElement.LegendElement.Size.Width;
                chartRect.Width -= legendRect.Width;
                break;
            case LegendPosition.Bottom:
                if (chart.ChartElement.TitlePosition == TitlePosition.Bottom)
                {
                    legendRect.Y = titleRect.Y - chart.ChartElement.LegendElement.Size.Height;
                }
                else
                {
                    legendRect.Y = size.Height - chart.ChartElement.LegendElement.Size.Height;
                }

                legendRect.Height = chart.ChartElement.LegendElement.Size.Height;
                chartRect.Height -= legendRect.Height;
                break;
            case LegendPosition.Left:
                legendRect.Width = chart.ChartElement.LegendElement.Size.Width;
                chartRect.X += legendRect.Width;
                chartRect.Width -= legendRect.Width;
                break;
            case LegendPosition.Top:
                legendRect.Height = chart.ChartElement.LegendElement.Size.Height;
                chartRect.Y += legendRect.Height;
                chartRect.Height -= legendRect.Height;
                break;
            case LegendPosition.Float:
                legendRect.Width = chart.ChartElement.LegendElement.Size.Width;
                legendRect.Height = chart.ChartElement.LegendElement.Size.Height;
                double xRatio = size.Width / this.Size.Width;
                double yRatio = size.Height / this.Size.Height;
                legendRect.X = (chart.ChartElement.LegendOffset.X * xRatio) + ((chart.ChartElement.TitlePosition == TitlePosition.Left)
                                                                               ? titleRect.Right : 0d);
                legendRect.Y = (chart.ChartElement.LegendOffset.Y * yRatio) + ((chart.ChartElement.TitlePosition == TitlePosition.Top)
                                                                               ? titleRect.Bottom : 0f);
                break;
        }
    }
    
    if (chart.ShowLegend)
    {
        float xTransform = (float)legendRect.X - chart.ChartElement.LegendElement.ControlBoundingRectangle.X +
                           ((float)legendRect.Width - chart.ChartElement.LegendElement.ControlBoundingRectangle.Width) / 2f;
        float yTransform = (float)legendRect.Y - chart.ChartElement.LegendElement.ControlBoundingRectangle.Y +
                           ((float)legendRect.Height - chart.ChartElement.LegendElement.ControlBoundingRectangle.Height) / 2f;
        graphics.TranslateTransform(xTransform, yTransform);
        chart.ChartElement.LegendElement.Paint(new RadGdiGraphics(graphics), chart.ChartElement.LegendElement.ControlBoundingRectangle, 0f,
            new SizeF(1f, 1f), true);
        graphics.ResetTransform();
    }
 
    RadGdiGraphics radGraphics = new RadGdiGraphics(graphics);

    if (chart.ShowTitle)
    {
        radGraphics.DrawString(chart.Title, GetTitleDrawRectangle(ChartRenderer.ToRectangleF(titleRect), titleSize,
            chart.ChartElement.TitleElement.TextAlignment), chart.ChartElement.TitleElement.Font,
            chart.ChartElement.TitleElement.ForeColor, chart.ChartElement.TitleElement.TextParams.CreateStringFormat(),
            chart.ChartElement.TitleElement.TextOrientation, chart.ChartElement.TitleElement.FlipText);
    }

    if (imageFormat == ImageFormat.Emf ||
        imageFormat == ImageFormat.Wmf)
    {
        Metafile metafile = new Metafile(stream, graphics.GetHdc()); // file is created here
        using (Graphics g = Graphics.FromImage(metafile))
        {
            g.DrawImage(bmp, Point.Empty);
        }

        metafile.Dispose();
        graphics.ReleaseHdc();
    }
    else
    {
        bmp.Save(stream, imageFormat);
    }

    chart.View.Layout();

    Image img = Image.FromStream(stream);
    graphics.DrawImage(img, new Point(0, 0));
    img.Save(filePath);
}

private RectangleF GetTitleDrawRectangle(RectangleF drawArea, SizeF textRect, ContentAlignment textAlignment)
{
    switch (textAlignment)
    {
        case ContentAlignment.BottomCenter:
            return new RectangleF(new PointF(drawArea.X + (drawArea.Width - textRect.Width) / 2f, drawArea.Bottom - textRect.Height), textRect);
        case ContentAlignment.BottomLeft:
            return new RectangleF(new PointF(drawArea.X, drawArea.Bottom - textRect.Height), textRect);
        case ContentAlignment.BottomRight:
            return new RectangleF(new PointF(drawArea.Right - textRect.Width, drawArea.Bottom - textRect.Height), textRect);
        case ContentAlignment.MiddleCenter:
            return new RectangleF(new PointF(drawArea.X + (drawArea.Width - textRect.Width) / 2f, drawArea.Y + (drawArea.Height - textRect.Height) / 2f), 
                textRect);
        case ContentAlignment.MiddleLeft:
            return new RectangleF(new PointF(drawArea.X, drawArea.Y + (drawArea.Height - textRect.Height) / 2f), textRect);
        case ContentAlignment.MiddleRight:
            return new RectangleF(new PointF(drawArea.Right - textRect.Width, drawArea.Y + (drawArea.Height - textRect.Height) / 2f), textRect);
        case ContentAlignment.TopCenter:
            return new RectangleF(new PointF(drawArea.X + (drawArea.Width - textRect.Width) / 2, drawArea.Y), textRect);
        case ContentAlignment.TopLeft:
            return new RectangleF(drawArea.Location, textRect);
        case ContentAlignment.TopRight:
            return new RectangleF(new PointF(drawArea.Right - textRect.Width, drawArea.Y), textRect);
        default:
            return new RectangleF(drawArea.Location, textRect);
    }
}

To reproduce:
Add stacked series with equal category that has negative values as well.

To reproduce:
- Set the title and the offset:
radChartView1.Title = "Test Title";
radChartView1.ShowTitle = true;
radChartView1.ChartElement.TitleElement.PositionOffset = new SizeF(100, 100);

- Export the chart.

Please refer to the attached sample project. Select a range from RadRangeSelector and print the chart. You will notice that the preview chart is shifted. Even if the the default margin is reduced to 0, the preview chart is not the same as the one displayed on the form.

Workaround: export the chart to a file which file can be printed: https://docs.telerik.com/devtools/winforms/controls/chartview/features/export

When you have BarSeries and LineSeries in RadChartView the problem is that the DataPoint.Presenter is always BarSerries, never LineSeries. 

To workaround, create custom renderer:

this.radChartView1.CreateRenderer += this.RadChartView1_CreateRenderer;
private void RadChartView1_CreateRenderer(object sender, ChartViewCreateRendererEventArgs e)
{
    e.Renderer = new CustomCartesianRenderer(e.Area as CartesianArea);
}

public class CustomCartesianRenderer : CartesianRenderer
{
    public CustomCartesianRenderer(CartesianArea area)
        : base(area)
    { }
    public override DataPoint HitTest(int x, int y)
    {
        for (int i = this.DrawParts.Count - 1; i >= 0; i--)
        {
            DataPoint dataPoint = this.DrawParts[i].HitTest(new Point(x, y));
            if (dataPoint != null)
            {
                return dataPoint;
            }
        }

        return base.HitTest(x, y);
    }
}