VB.Net - First dataPoint in series plotting to wrong x value on chart

Question

I'm developing a class to manage data Series for a chart. However, when I add a new series, if the first dataPoint has an XValue of 0, it instead shows on the plot as having an XValue of 1. If I add an additional dataPoint, it seems to correct itself. Using the code below, the constructor is called first(obviously), then Initialize(with data like "Series1",0,0), then AddPoint can be called later. Anyone know what is going on?

Edit: From what I've found, this occurs any time the Series has only one data point and that data point has an xValue of 0. The series also does not behave correctly until one(or sometime more) data points with non-zero xValues are added. My workaround is if a data point to be added has an xValue of 0, make its xValue extremely small instead(1x10^-150). Seems to work, but this is still an odd bug in my book. I haven't been able to find any information on it either.

Public Sub New(ByVal chartObj As Chart)
    'Init m_chart
    m_chart = chartObj

    m_chart.BackColor = Color.Gainsboro

    'Init Legend
    m_legend = New Legend("Legend")
    m_legend.Docking = Docking.Bottom
    m_chart.Legends.Add(m_legend)

    'Init m_chartArea

    m_chartArea = New ChartArea("Default")

    m_chartArea.BackColor = Color.Black

    m_chartArea.AxisX.LabelStyle.Format = "{0:0.00}"

    setXLimits(-10, 10)
    setYLimits(-0.5, 0.5)

    m_chartArea.AxisX.Title = "Position (mm)"
    m_chartArea.AxisX.TitleFont = New Font("Arial", 10, FontStyle.Regular)

    m_chartArea.AxisY.Title = "Peak-To-Peak (Volts)"
    m_chartArea.AxisY.TitleFont = New Font("Arial", 10, FontStyle.Regular)

    m_chartArea.AxisX.MajorGrid.LineDashStyle = ChartDashStyle.Dash
    m_chartArea.AxisX.MajorGrid.LineColor = Color.DarkGreen
    m_chartArea.AxisY.MajorGrid.LineDashStyle = ChartDashStyle.Dash
    m_chartArea.AxisY.MajorGrid.LineColor = Color.DarkGreen

    m_chart.ChartAreas.Add(m_chartArea)

    'Init m_dataSeries
    m_dataSeries = New List(Of Series)

    'Init m_markerSeries
    m_markerSeries = New Series("Peaking Markers")
    m_markerSeries.ChartType = SeriesChartType.Point
    m_markerSeries.MarkerColor = Color.Red
    m_markerSeries.MarkerStyle = MarkerStyle.Triangle
    m_markerSeries.MarkerSize = 10
    m_chart.Series.Add(m_markerSeries)

    'Init m_title
    m_title = New Title("Plots")
    m_title.Font = New Font("Arial", 20, FontStyle.Regular)
    m_chart.Titles.Add(m_title)

End Sub

Public Sub Initialize(ByVal Legend As String, ByVal xVal As Double, ByVal yVal As Double)
    Dim temp As New Series(Legend)
    temp.ChartType = SeriesChartType.Line
    temp.Points.Clear()

    If nextAxis = "X" Then
        temp.Color = xColor
        nextAxis = "Y"
    Else
        temp.Color = yColor
        nextAxis = "X"
    End If

    temp.MarkerStyle = MarkerStyle.Circle

    m_dataSeries.Add(temp)
    m_chart.Series.Add(temp)

    AddPoint(xVal, yVal)

End Sub

Public Sub AddPoint(ByVal x As Double, ByVal y As Double)
    If m_chart.InvokeRequired Then
        m_chart.Invoke(New Action(Of Double, Double)(AddressOf AddPoint), x, y)
    Else
        Dim temp As New DataPoint(x, y)

        m_dataSeries.Item(m_dataSeries.Count - 1).Points.Add(temp)
    End If
End Sub

Benjo Benjo · Accepted Answer · 2014-04-15T08:11:36

Try changing this:

If m_chart.InvokeRequired Then
    m_chart.Invoke(New Action(Of Double, Double)(AddressOf AddPoint), x, y)
Else
    Dim temp As New DataPoint(x, y)

    m_dataSeries.Item(m_dataSeries.Count - 1).Points.Add(temp)
End If

To this:

If m_chart.InvokeRequired Then
    m_chart.Invoke(New Action(Of Double, Double)(AddressOf AddPoint), x, y)
End If

Dim temp As New DataPoint(x, y)
m_dataSeries.Item(m_dataSeries.Count - 1).Points.Add(temp)

VB.Net - First dataPoint in series plotting to wrong x value on chart

2 Answers