VB2008中用GDI+画图的问题

Question

用以下代码在PictureBoxTemperature001中绘图，怎么会没有显示？语法没有任何错误。
控件PictureBoxTemperature001位于窗体Form1中的一个控件 TabControl 上
若PictureBoxTemperature001直接在窗体Form1中可以显示。
输入时Me. 后面自动出现的PictureBoxTemperature001
'图形显示
Dim graTemp001 As Graphics = Me.PictureBoxTemperature001.CreateGraphics
Dim intWidthAll, intHeightAll As Integer
intWidthAll = PictureBoxTemperature001.Width
intHeightAll = PictureBoxTemperature001.Height

'绘制矩形
Dim intX1, intY1, intWidth, intHeight, intWWW As Integer
intWWW = 10 '矩形到Picture边界的距离
intX1 = intWWW : intY1 = intWWW
intWidth = intWidthAll - 2 * intWWW : intHeight = intHeightAll - 2 * intWWW

Dim MyPen As New Pen(Color.BlueViolet, 2)
Dim MyPen1 As New Pen(Color.Red, 3)
Dim rect As New Rectangle(intX1, intY1, intWidth, intHeight)
'左上角位于 (intX1, intY1) 的矩形。该矩形的宽度为 intWidth，高度为intHeight
graTemp001.DrawRectangle(MyPen, rect)

Answer 1

因为一刷新图就消失了，控件 TabControl上会自动刷新，在Form1_Paint中绘制可避免

或者改成下面的代码

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        PictureBoxTemperature001.Image = Nothing
        Dim intWidthAll, intHeightAll As Integer
        intWidthAll = PictureBoxTemperature001.Width
        intHeightAll = PictureBoxTemperature001.Height
        Dim bm As New Bitmap(intWidthAll, intHeightAll)
        Dim graTemp001 As Graphics = Graphics.FromImage(bm)
        '绘制矩形
        Dim intX1, intY1, intWidth, intHeight, intWWW As Integer
        intWWW = 10                '矩形到Picture边界的距离
        intX1 = intWWW : intY1 = intWWW
        intWidth = intWidthAll - 2 * intWWW : intHeight = intHeightAll - 2 * intWWW
        Dim MyPen As New Pen(Color.BlueViolet, 2)
        Dim MyPen1 As New Pen(Color.Red, 3)
        Dim rect As New Rectangle(intX1, intY1, intWidth, intHeight)
        '左上角位于 (intX1, intY1) 的矩形。该矩形的宽度为 intWidth，高度为intHeight
        graTemp001.DrawRectangle(MyPen, rect)
        PictureBoxTemperature001.Image = bm
        PictureBoxTemperature001.Refresh()
        graTemp001.Dispose()
    End Sub