Mouse MOve event - Show values in a MS Chart Control

Question

Below is sample code, with sample values. Uses a Form with a Chart object ("Chart1") X-Axis is the date and there are 2 Y values. If the mouse passes over the line(s) I want to display which series, the value and the date, several show as "Unknown" because the value passed to the Function is slightly off the actual value. I'd rather NOT use the function I created anyway, I would rather get it direct from the HitTest results if that is possible.

Option Strict On
Imports System.Windows.Forms.DataVisualization.Charting

Public Class Form1
    Private TheDate As New List(Of Date)
    Private Series1 As New List(Of Integer)
    Private Series2 As New List(Of Integer)

    Private Function DateFromOtherData(SName As String, Data As Integer) As String
        Dim DataIndex As Integer = -1
        If SName = "Series1" Then
            DataIndex = Series1.IndexOf(Data)
        Else
            DataIndex = Series2.IndexOf(Data)
        End If
        If DataIndex > -1 Then
            Return TheDate(DataIndex).ToShortDateString
        Else
            Return "Unknown"
        End If

    End Function
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        'Add some saple data
        Dim Temp As New List(Of String)
        Temp.Add("2020-03-07")
        Series1.Add(428)
        Series2.Add(19)
        Temp.Add("2020-03-31")
        Series1.Add(188461)
        Series2.Add(4304)
        Temp.Add("2020-04-24")
        Series1.Add(909853)
        Series2.Add(51360)
        Temp.Add("2020-05-18")
        Series1.Add(1515593)
        Series2.Add(90414)
        Temp.Add("2020-06-11")
        Series1.Add(2036500)
        Series2.Add(113980)
        Temp.Add("2020-07-05")
        Series1.Add(2910782)
        Series2.Add(129941)
        Temp.Add("2020-07-29")
        Series1.Add(4433633)
        Series2.Add(151172)
        Temp.Add("2020-09-15")
        Series1.Add(6614318)
        Series2.Add(195689)
        Temp.Add("2020-10-09")
        Series1.Add(7719211)
        Series2.Add(213595)
        Temp.Add("2020-11-02")
        Series1.Add(9377208)
        Series2.Add(231480)
        Temp.Add("2020-11-26")
        Series1.Add(12954294)
        Series2.Add(263339)
        Temp.Add("2020-12-20")
        Series1.Add(17880478)
        Series2.Add(317810)
        Temp.Add("2021-01-13")
        Series1.Add(23135194)
        Series2.Add(384824)
        Temp.Add("2021-02-06")
        Series1.Add(26958807)
        Series2.Add(462052)
        Temp.Add("2021-03-02")
        Series1.Add(28738501)
        Series2.Add(515710)
        Temp.Add("2021-03-26")
        Series1.Add(30172762)
        Series2.Add(547621)
        Temp.Add("2021-04-19")
        Series1.Add(31754642)
        Series2.Add(567314)
        Temp.Add("2021-05-13")
        Series1.Add(32868084)
        Series2.Add(583991)
        Temp.Add("2021-06-06")
        Series1.Add(33329413)
        Series2.Add(596803)
        Temp.Add("2021-06-30")
        Series1.Add(33639764)
        Series2.Add(604446)
        Temp.Add("2021-07-24")
        Series1.Add(34469200)
        Series2.Add(610400)
        Temp.Add("2021-08-17")
        Series1.Add(37133674)
        Series2.Add(623237)
        Temp.Add("2021-09-10")
        Series1.Add(40914456)
        Series2.Add(658865)
        Temp.Add("2021-10-04")
        Series1.Add(43826566)
        Series2.Add(703362)
        Temp.Add("2021-10-28")
        Series1.Add(45797078)
        Series2.Add(743050)
        Temp.Add("2021-11-21")
        Series1.Add(47692614)
        Series2.Add(771871)
        Temp.Add("2021-12-15")
        Series1.Add(50346987)
        Series2.Add(801037)
        'For i = 0 To Series1.Count - 1         'This lowers each value in Series1
        'Series1(i) = CInt(Series1(i) / 50)     'and makes getting the date work
        'Next                                   'Not acceptable, just an example
        For Each S As String In Temp
            TheDate.Add(CDate(S))
        Next
    End Sub

    Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles Me.Shown
        Chart1.Series.Clear()
        Chart1.Series.Add("Series1")
        Chart1.Series.Add("Series2")
        Chart1.Series(0).YAxisType = AxisType.Primary
        Chart1.Series(1).YAxisType = AxisType.Secondary
        Chart1.ChartAreas(0).AxisY.MajorGrid.LineWidth = 0
        Chart1.ChartAreas(0).AxisY2.MajorGrid.LineWidth = 0
        Chart1.ChartAreas(0).AxisX.MajorGrid.LineWidth = 0
        Chart1.ChartAreas(0).AxisX2.MajorGrid.LineWidth = 0
        Chart1.ChartAreas(0).AxisX.Interval = 21
        Chart1.ChartAreas(0).AxisX2.Interval = 21
        Chart1.ChartAreas(0).AxisY.LabelStyle.ForeColor = Color.Blue
        Chart1.ChartAreas(0).AxisY.LabelStyle.Font = New Font("Arial", 12, FontStyle.Bold)
        Chart1.ChartAreas(0).AxisY2.LabelStyle.ForeColor = Color.Red
        Chart1.ChartAreas(0).AxisY2.LabelStyle.Font = New Font("Arial", 12, FontStyle.Bold)

        Chart1.Series(0).Name = "Series1"
        Chart1.Series(0).Points.DataBindXY(TheDate.ToArray, Series1.ToArray)
        Chart1.Titles.Clear()
        Chart1.Series(1).Name = "Series2"
        Chart1.Series(1).Points.DataBindXY(TheDate.ToArray, Series2.ToArray)
        Chart1.Series(0).ChartType = SeriesChartType.Line
        Chart1.Series(0).BorderWidth = 5
        Chart1.Series(1).ChartType = SeriesChartType.Line
        Chart1.Series(1).BorderWidth = 2

        Chart1.Series(0).Color = Color.Blue
        Chart1.Series(1).Color = Color.Red

        Chart1.Visible = True
    End Sub

    Private Sub Chart1_MouseMove(sender As Object, e As MouseEventArgs) Handles Chart1.MouseMove

        Dim result As HitTestResult = Chart1.HitTest(e.X, e.Y)
        Dim Ndx As Integer
        Dim thisPt As New PointF
        Dim ta As New CalloutAnnotation
        Dim TheText As String = ""

        Chart1.Annotations.Clear()
        If result.ChartElementType = ChartElementType.DataPoint Then

            Dim SName As String = result.Series.Name
            If SName = "Series1" Then
                Ndx = 0
            Else
                Ndx = 1
            End If
            thisPt = New PointF(CSng(Chart1.Series(Ndx).Points(result.PointIndex).XValue),
                                CSng(Chart1.Series(Ndx).Points(result.PointIndex).YValues(0)))

            ta.CalloutStyle = CalloutStyle.Rectangle
            ta.AnchorDataPoint = Chart1.Series(Ndx).Points(result.PointIndex)
            ta.Alignment = ContentAlignment.MiddleLeft
            ta.TextStyle = TextStyle.Default
            ta.Font = New Font("Arial", 10, FontStyle.Bold)

            TheText &= SName & ": " & vbLf &
                "Value: " & thisPt.Y.ToString("F0") & vbLf &
                "Date: " & DateFromOtherData(SName, CInt(thisPt.Y))
            ta.Text = TheText
            Chart1.Annotations.Add(ta)
            Chart1.Invalidate()
            Me.Text = "ThisPt.X = " & thisPt.X.ToString
        End If
    End Sub
End Class

Answer 1

Try this modification:

TheText &= SName & ": " & vbLf &
                "Value: " & thisPt.Y.ToString("F0") & vbLf &
                "Date: " & Date.FromOADate(thisPt.X) 

Answer 2

Hi @Devon Nullman ，
The problem occurs in lines 165 and 166 of your code.
When DataPoint.XValue is converted from double type to single type, the precision is lost and the data is distorted.
You can choose to use List(Of Double) to avoid this problem.
Here is the code I modified based on your code.

    Private Series1 As New List(Of Double)  
    Private Series2 As New List(Of Double)  
  
    Private Function DateFromOtherData(SName As String, Data As Double) As String  
        Dim DataIndex As Integer = -1  
        If SName = "Series1" Then  
            DataIndex = Series1.IndexOf(Data)  
        Else  
            DataIndex = Series2.IndexOf(Data)  
        End If  
        If DataIndex > -1 Then  
            Return TheDate(DataIndex).ToShortDateString  
        Else  
            Return "Unknown"  
        End If  
  
    End Function  
  
    Private Sub Chart1_MouseMove(sender As Object, e As MouseEventArgs) Handles Chart1.MouseMove  
  
        Dim result As HitTestResult = Chart1.HitTest(e.X, e.Y)  
        Dim Ndx As Integer  
        Dim ta As New CalloutAnnotation  
        Dim TheText As String = ""  
  
        Chart1.Annotations.Clear()  
        If result.ChartElementType = ChartElementType.DataPoint Then  
  
            Dim SName As String = result.Series.Name  
            If SName = "Series1" Then  
                Ndx = 0  
            Else  
                Ndx = 1  
            End If  
  
            ta.CalloutStyle = CalloutStyle.Rectangle  
            ta.AnchorDataPoint = Chart1.Series(Ndx).Points(result.PointIndex)  
            ta.Alignment = ContentAlignment.MiddleLeft  
            ta.TextStyle = TextStyle.Default  
            ta.Font = New Font("Arial", 10, FontStyle.Bold)  
  
            TheText &= SName & ": " & vbLf &  
                "Value: " & Chart1.Series(Ndx).Points(result.PointIndex).YValues(0) & vbLf &  
                "Date: " & DateFromOtherData(SName, Chart1.Series(Ndx).Points(result.PointIndex).YValues(0))  
            ta.Text = TheText  
            Chart1.Annotations.Add(ta)  
            Chart1.Invalidate()  
            Me.Text = "ThisPt.X = " & Chart1.Series(Ndx).Points(result.PointIndex).XValue  
        End If  
    End Sub  

Hope the code above could be helpful.
Best Regards.
Jiachen Li

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