我用picturebox控件进行画线操作。涉及到2个函数（自己定义）。
    '----****----****----****----****----****----****----****----'
    ''函数:  DrawVI()
    ''功能：画曲线。
    '----****----****----****----****----****----****----****----'
    Public Sub DrawVI(ByVal index As Integer, ByVal TVP As PictureBox, ByVal Vol As Single, ByVal Cur As Single)
        Dim BeginningV As Point
        Dim EndingV As Point
        Dim BeginningI As Point
        Dim EndingI As Point
        Dim Yaxis_V As Single
        Dim Yaxis_I As Single
        Dim i As Integer
        Dim VTZB As Graphics = TVP.CreateGraphics()

        XStep(index) = 0.21 * (50 / XUnit(index))
        Xnew(index) = Xnew(index) + XStep(index)
        Yaxis_V = 280 - Vol / (SetVol(index) * 1.4) * 280            '电压
        Yaxis_I = 280 - Cur / (SetCur(index) * 1.4) * 280          '电流

        BeginningV.X = Xnew(index)
        BeginningV.Y = Yaxis_V
        EndingV.X = Xold(index)
        EndingV.Y = YVold(index)
        VTZB.DrawLine(Pens.Blue, BeginningV, EndingV)         '画电压曲线

        BeginningI.X = Xnew(index)
        BeginningI.Y = Yaxis_I
        EndingI.X = Xold(index)
        EndingI.Y = YIold(index)
        VTZB.DrawLine(Pens.Red, BeginningI, EndingI)          '画电流曲线

        Xold(index) = Xnew(index)
        YVold(index) = Yaxis_V
        YIold(index) = Yaxis_I

        If Xnew(index) > 280 Then
            XUnit(index) = XUnit(index) * 1.25
            Xnew(index) = 5
            Xold(index) = 5
            YVold(index) = 280
            YIold(index) = 280
            Test = True
            Select Case index
                Case 0
                   LineZB(0, TVP1, SetVol(0), SetCur(0))             '///////////////////重新坐标轴绘制部分/////////////////////
                    For i = 1 To SerialNum(0)
                        DrawVI(0, TVP1, VolSave(0, i), CurSave(0, i))’///////////////////重新曲线绘制部分/////////////////////
                    Next

                Case 1
                    LineZB(1, TVP2, SetVol(1), SetCur(1))
                    For i = 1 To SerialNum(1)
                        DrawVI(1, TVP2, VolSave(1, i), CurSave(1, i))
                    Next
                Case 2
                    LineZB(2, TVP3, SetVol(2), SetCur(2))
                    For i = 1 To SerialNum(2)
                        DrawVI(2, TVP3, VolSave(2, i), CurSave(2, i))
                    Next
            End Select
        End If
        Me.Invalidate()
        VTZB.Dispose()
    End Sub

 ''画坐标轴
    Public Sub LineZB(ByVal index As Integer, ByVal TVP As PictureBox, ByVal LineV As Single, ByVal LineI As Single)
        Dim Beginning As Point
        Dim Ending As Point
        Dim i As Byte
        Dim TimeZB, VolZB, CurZB As String
        Dim MyFont As Font

        MyFont = New System.Drawing.Font("宋体", 9)
        TVP.Image = New Bitmap(TVP.Width, TVP.Height)
        Dim VTZB As Graphics = Graphics.FromImage(TVP.Image)
        '画外框
        VTZB.DrawRectangle(Pens.Black, 5, 0, 280, 280)
        '画横坐标
        For i = 0 To 5
            Beginning.X = 45 + i * 40
            Beginning.Y = 0
            Ending.X = 45 + i * 40
            Ending.Y = 280
            VTZB.DrawLine(Pens.DarkGray, Beginning, Ending)
        Next i
        '画纵坐标
        For i = 0 To 5
            Beginning.X = 5
            Beginning.Y = 40 + i * 40
            Ending.X = 285
            Ending.Y = 40 + i * 40
            VTZB.DrawLine(Pens.DarkGray, Beginning, Ending)
        Next i
        '画刻度
        For i = 0 To 7
            Beginning.X = i * 38
            Beginning.Y = 280
            TimeZB = CStr(Format(i * XUnit(index), "0"))
            VTZB.DrawString(TimeZB, MyFont, System.Drawing.Brushes.Black, Beginning.X, Beginning.Y)
        Next

        For i = 0 To 6
            Beginning.X = 5
            Beginning.Y = 228 - i * 38
            Ending.X = 265
            Ending.Y = 228 - i * 38
            VolZB = LineV * 1.4 / 7 * (i + 1)
            CurZB = LineI * 1.4 / 7 * (i + 1)
            VTZB.DrawString(VolZB, MyFont, System.Drawing.Brushes.Black, Beginning.X, Beginning.Y)
            VTZB.DrawString(CurZB, MyFont, System.Drawing.Brushes.Black, Ending.X, Ending.Y)
        Next

        Me.Invalidate()
        VTZB.Dispose()
    End Sub

我调用DrawVI，当曲线画到头时，我重新绘制坐标轴，并将先前保存在数据缓冲区中的数据重新绘制曲线，然后再接着进行绘图(仍调用DrawVI).
但是在picturebox中，重新绘制曲线部分为空白，详细见附件图：

请问各位高手，空白部分是怎么回事，怎么样避免。我试了N种办法，都是行不通。
谢谢。

[ 本帖最后由 galaxing 于 2012-10-15 21:35 编辑 ]