.net 我怎样才能用画上的内容重新画一个画框？

我有一个picturebox，可以获得类似以下内容的输出：

e = New PrintPageEventArgs(PictureBox1.CreateGraphics, New Rectangle(New Point(25, 25), New Size(New Point(825, 1075))), e.PageBounds, e.PageSettings)

'Draw box
e.Graphics.DrawRectangle(Pens.Gray, 20, 30, e.PageBounds.Width - 100, e.PageBounds.Height - 130)

DrawnImage = PictureBox1.Image

我需要在绘画活动中更新它：

Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint

    PictureBox1.Image = DrawnImage 

End Sub

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问题是DrawnImage为NULL。如何捕获图像？

我需要使用位图，而不是从picturebox创建图形对象

有关完整的说明，请参见此处：

Dim b As New Bitmap(PictureBox1.Width, PictureBox1.Height)

e = New PrintPageEventArgs(Graphics.GraphicsFromImage(b), New Rectangle(New Point(25, 25), New Size(New Point(825, 1075))), e.PageBounds, e.PageSettings)

'Draw box
e.Graphics.DrawRectangle(Pens.Gray, 20, 30, e.PageBounds.Width - 100, e.PageBounds.Height - 130)

PictureBox1.Image = b