How to stop controls from flickering during MouseMove Event - vb.net

Question

I know this is a pretty popular question, but none of the solutions I have found have worked for me.
Background: I have a windows forms project in VS2015 that reads data from text files and plots the data as multiple series on a line chart. The Chart.MouseMove event finds the point nearest the mouse and draws a circle around it. The circle is drawn in the Chart_Paint event
Private Sub crtLogView(sender As Object,e As PaintEventArgs) Handles crtLogView.Paint
Dim whitePen as New Pne(Color.White,2)
e.Graphics.DrawEllipse(whitePen,cir) '//cir is a Public Rectangle
End Sub
When moving the mouse across the chart, random controls flicker off then back on which is very annoying. I have posted the MouseMove event code below.
Potential solutions I have tried:
Turning on the DoubleBuffered property of the form, which does nothing
Using the Me.Invalidate() and Me.Update() method, which does not move the circle
Using the Chart.Invalidate() and Chart.Update() method, which works, but is very slow
Adding the following code to my Form_Load routine, which appears to do nothing
Any help with this would be greatly appreciated
Me.SetStyle(ControlStyles.AllPaintingInWmPaint, True)
Me.SetStyle(ControlStyles.DoubleBuffer, True)
Me.SetStyle(ControlStyles.UserPaint, True)
MouseMove Event Code:
Private Sub crtLogView_MouseMove(sender As Object, e As MouseEventArgs) Handles crtLogView.MouseMove
'//Show data for closest point to cursor & draw circle around point
Dim hResult As HitTestResult = crtLogView.HitTest(e.X, e.Y)
Dim srsNam As String = ""
Dim mouseY As Single
Dim pntDist As Double = 0
Dim pntX As Single
Dim pntY As Single
Dim mouseX As Single
On Error GoTo ErrTrap
'//Get X-Axis Position as integer
mouseX = Int(hResult.ChartArea.AxisX.PixelPositionToValue(e.X))
'// Set time value
lblTime.Text = String.Format("{0:n2}", hResult.ChartArea.AxisX.PixelPositionToValue(e.X) / 160)
'//Get Y-Axis Position
mouseY = hResult.ChartArea.AxisY.PixelPositionToValue(e.Y)
'//Get distance from mouse to point on Series(0)
pntDist = Math.Abs(crtLogView.Series(0).Points(mouseX).YValues(0) - mouseY)
srsNam = crtLogView.Series(0).Name '//1st series name
'//Find closest series
For i As Integer = 1 To crtLogView.Series.Count - 1
If Math.Abs(crtLogView.Series(i).Points(mouseX).YValues(0) - mouseY) < pntDist Then
pntDist = Math.Abs(crtLogView.Series(i).Points(mouseX).YValues(0) - mouseY)
srsNam = crtLogView.Series(i).Name
End If
Next
'//Set Top/Left values for circle
pntY = crtLogView.ChartAreas(0).AxisY.ValueToPixelPosition(crtLogView.Series(srsNam).Points(mouseX).YValues(0)) - 4
pntX = crtLogView.ChartAreas(0).AxisX.ValueToPixelPosition(Val(mouseX)) - 4
'//Move circle to closest point
cir.Location = New Point(pntX, pntY)
'//Refresh the form to move the circle
'//This works, but takes 2+ seconds to take effect
'crtLogView.Invalidate()
'crtLogView.Update()
'//This does not work
'Me.Invalidate()
'Me.Update()
'//This works, but randomly makes other controls flash/flicker
Me.Refresh()
ErrTrap:
End Sub

Answer 1

In the comments, I offered to provide an example of using a Chart Annotation or a DataPoint Label as an alternative to custom painting a circle around the point under the mouse-cursor and have included that in the code below. However, I realized that a DataPoint Marker should provide the function the OP is seeking and is likely the proper solution. Therefore, that option is also included.
Annotations are chart level graphics where-as the DataPoint Label and DataPoint Marker are as the name implies tied to the individual DataPoints. Proper sizing of annotations can be involved as their size is specified as a percentage of the Chart Area dimensions. This example does not attempt to resize the annotation based on the current chart size.
The following code sample is for a WinForm. In VS, add a new Class to a WinForm project and replace the auto-generated code with this. The set this Form as the startup Form.
Imports System
Imports System.Drawing
Imports System.Windows.Forms
Imports Charting = System.Windows.Forms.DataVisualization.Charting
Public Class ChartDemo : Inherits Form
Const yMultiplyer As Double = 100.0
Private rnd As Random
Friend WithEvents chart As System.Windows.Forms.DataVisualization.Charting.Chart
Friend WithEvents rbAnnotation As System.Windows.Forms.RadioButton
Friend WithEvents rbDataLabel As System.Windows.Forms.RadioButton
Friend WithEvents rbMarker As System.Windows.Forms.RadioButton
Private lastPoint As Charting.DataPoint
Private ellispeAnnotation As Charting.EllipseAnnotation
Public Sub New()
InitializeComponent()
rnd = New Random(0) ' use same basis for each run
SetupChart()
End Sub
Private Sub InitializeComponent()
Me.chart = New System.Windows.Forms.DataVisualization.Charting.Chart()
Me.rbAnnotation = New System.Windows.Forms.RadioButton()
Me.rbDataLabel = New System.Windows.Forms.RadioButton()
Me.rbMarker = New System.Windows.Forms.RadioButton()
CType(Me.chart, System.ComponentModel.ISupportInitialize).BeginInit()
Me.SuspendLayout()
Me.chart.Anchor = AnchorStyles.Top Or
AnchorStyles.Bottom Or
AnchorStyles.Left Or
AnchorStyles.Right
Me.chart.Location = New Point(4, 50)
Me.chart.Size = New Size(600, 500)
Me.rbAnnotation.AutoSize = True
Me.rbAnnotation.Location = New Point(50, 10)
Me.rbAnnotation.TabIndex = 1
Me.rbAnnotation.Text = "Use Annotation"
Me.rbAnnotation.UseVisualStyleBackColor = True
Me.rbDataLabel.AutoSize = True
Me.rbDataLabel.Location = New Point(200, 10)
Me.rbDataLabel.TabIndex = 2
Me.rbDataLabel.Text = "Use Data Label"
Me.rbDataLabel.UseVisualStyleBackColor = True
Me.rbMarker.AutoSize = True
Me.rbMarker.Location = New Point(400, 10)
Me.rbMarker.TabIndex = 3
Me.rbMarker.Text = "Use Data Marker"
Me.rbMarker.UseVisualStyleBackColor = True
Me.rbMarker.Checked = True
Me.AutoScaleDimensions = New SizeF(96.0!, 96.0!)
Me.AutoScaleMode = AutoScaleMode.Dpi
Me.ClientSize = New Size(610, 555)
Me.Controls.AddRange({Me.rbDataLabel, Me.rbAnnotation, Me.rbMarker, Me.chart})
Me.Text = "Charting Demo"
CType(Me.chart, System.ComponentModel.ISupportInitialize).EndInit()
Me.ResumeLayout(False)
Me.PerformLayout()
End Sub
Private Sub SetupChart()
chart.ChartAreas.Clear()
chart.Legends.Clear()
chart.Series.Clear()
chart.Annotations.Clear()
Dim area1 As New Charting.ChartArea("Area1")
chart.ChartAreas.Add(area1)
Dim ser As Charting.Series = chart.Series.Add("Series1")
ser.ChartArea = area1.Name
ser.ChartType = Charting.SeriesChartType.Line
' define defaults for point DataLabels
ser.LabelBorderColor = Color.Red
ser.LabelBorderWidth = 1
ser.LabelBackColor = Color.WhiteSmoke
ser.LabelForeColor = Color.Black
' define defaults for point DataMarkers
ser.MarkerSize = 10
ser.MarkerBorderWidth = 3
ser.MarkerBorderColor = Color.Red
ser.MarkerColor = Color.Transparent
' points for demo chart
For x As Double = -5.0 To 5.0
ser.Points.AddXY(x, rnd.NextDouble * yMultiplyer)
Next
ellispeAnnotation = CreateEllipseAnnotation()
ellispeAnnotation.Visible = False
chart.Annotations.Add(ellispeAnnotation)
End Sub
Private Sub chart_MouseLeave(sender As Object, e As EventArgs) Handles chart.MouseLeave
ellispeAnnotation.Visible = False
ClearLastPointDataLabel()
ClearLastPointMarker()
End Sub
Private Function CreateEllipseAnnotation() As Charting.EllipseAnnotation
Dim ret As New Charting.EllipseAnnotation()
ret.ForeColor = Color.Black
ret.Font = New Font("Arial", 10)
ret.LineWidth = 2
ret.Height = 7.5 ' % ChartArea height
ret.Width = 15 ' % ChartArea width
ret.BackColor = Color.PaleGoldenrod
ret.LineDashStyle = Charting.ChartDashStyle.Solid
Return ret
End Function
Private Sub chart_MouseMove(sender As Object, e As MouseEventArgs) Handles chart.MouseMove
Dim htr As Charting.HitTestResult = chart.HitTest(e.X, e.Y)
If htr.ChartElementType = Charting.ChartElementType.DataPoint Then
Dim pt As Charting.DataPoint = DirectCast(htr.Object, Charting.DataPoint)
If pt IsNot lastPoint Then
SetDataPointLabel(pt)
SetDataPointAnnotation(pt)
SetDataPointMarker(pt)
lastPoint = pt
End If
End If
End Sub
Private Sub SetDataPointAnnotation(pt As Charting.DataPoint)
If rbAnnotation.Checked Then
ellispeAnnotation.AnchorDataPoint = pt
ellispeAnnotation.Text = String.Format("{0:N2}, {1:N2}", pt.XValue, pt.YValues(0))
ellispeAnnotation.Visible = True
End If
End Sub
Private Sub SetDataPointLabel(pt As Charting.DataPoint)
ClearLastPointDataLabel()
If rbDataLabel.Checked Then
pt.Label = "#VALX{N2}, #VALY{N2}" ' case sensative, use uppercase for #VALX, #VALY
pt.IsValueShownAsLabel = True
End If
End Sub
Private Sub ClearLastPointDataLabel()
If lastPoint IsNot Nothing Then
lastPoint.Label = String.Empty
lastPoint.IsValueShownAsLabel = False
End If
End Sub
Private Sub SetDataPointMarker(pt As Charting.DataPoint)
ClearLastPointMarker()
If rbMarker.Checked Then pt.MarkerStyle = Charting.MarkerStyle.Circle
End Sub
Private Sub ClearLastPointMarker()
If lastPoint IsNot Nothing Then
lastPoint.MarkerStyle = Charting.MarkerStyle.None
End If
End Sub
Private Sub rbAnnotation_CheckedChanged(sender As Object, e As EventArgs) Handles rbAnnotation.CheckedChanged
If Not rbAnnotation.Checked Then
ellispeAnnotation.Visible = False
End If
End Sub
Private Sub rbDataLabel_CheckedChanged(sender As Object, e As EventArgs) Handles rbDataLabel.CheckedChanged
ClearLastPointDataLabel()
End Sub
Private Sub rbMarker_CheckedChanged(sender As Object, e As EventArgs) Handles rbMarker.CheckedChanged
ClearLastPointMarker()
End Sub
End Class