Hello, I have a problem concerning drawing on a panel. What I need to do is create a timeline, meaning I draw some vertical and horizontal lines. The problem occurs when I scroll the panel. All the drawing that should be in the scrolled area dissappears. I tried to set the paint event of the panel, but then it just draws the lines chaotically (one vertical line just after the other, not at specified intervals). I have no idea what to try further on.

Here is my code, with just the vertical lines: (drawing is performed on a panel -Panel1)

Public Class Form1

    Public lines As New ArrayList


    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        DrawLines()
    End Sub


    Private Sub DrawLines()
        Dim myVerticalPen As New System.Drawing.Pen(System.Drawing.Color.Black, 3)
        Dim myHorizontalPen As New System.Drawing.Pen(System.Drawing.Color.BlueViolet, 10)
        Dim formGraphics As System.Drawing.Graphics
        Dim dashValues As Single() = {5, 2, 10, 4}
        Dim blackPen As New System.Drawing.Pen(System.Drawing.Color.Black, 1)

        Dim datesLabelArray(20) As Label 'create an array of labels for the date(horizontal) part of the timeline
        Dim CurrD As DateTime = "07/12/2012"
        Dim labelPosX As Integer = 100
        Dim labelPosY As Integer = 50

        Dim line As Line
        formGraphics = Panel1.CreateGraphics()
        blackPen.DashPattern = dashValues

        'display vertical part of timeline (partno labels)
        Dim partsLabelArray(15) As Label 'create an array of labels for the part(vertical) part of the timeline

        For x = 0 To partsLabelArray.Length - 1 'initialize the array of labels
            partsLabelArray(x) = New Label
            partsLabelArray(x).Name = "myPartLabel" + x.ToString()
            partsLabelArray(x).Text = "mypart" + x.ToString()
            partsLabelArray(x).Visible = True 'Initializing the TextBox so that it is not rendered in the browser 
            partsLabelArray(x).AutoSize = True
            partsLabelArray(x).Left = 10
            partsLabelArray(x).Top = labelPosY

            Panel1.Controls.Add(partsLabelArray(x)) 'Adding the TextBox to the Panel that holds the text boxes. 
            CurrD = CurrD.AddDays(1)
            labelPosY += 30
        Next x

        CurrD = "07/12/2012"

        For x = 0 To datesLabelArray.Length - 1 'initialize the array of labels
            datesLabelArray(x) = New Label
            datesLabelArray(x).Name = "myDateLabel" + x.ToString()
            datesLabelArray(x).Text = CurrD
            datesLabelArray(x).Visible = True 'Initializing the TextBox so that it is not rendered in the browser 
            datesLabelArray(x).AutoSize = True
            datesLabelArray(x).Left = labelPosX + 20
            datesLabelArray(x).Top = 20

            line = New Line(myVerticalPen, formGraphics, New Point(labelPosX + 110, 50), New Point(labelPosX + 110, labelPosY - 50))
            'line.Draw()
            lines.Add(line)

            Panel1.Controls.Add(datesLabelArray(x)) 'Adding the TextBox to the Panel that holds the text boxes. 
            CurrD = CurrD.AddDays(1)
            labelPosX += 120
        Next x

        Panel1.Invalidate()
        Panel1.Update()


    End Sub



    Private Sub Form1_Paint(sender As System.Object, e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        For Each linie As Line In lines
            linie.Draw()
        Next linie
    End Sub
End Class