删除另一个窗口下的部分PictureBox

Question

我正在使用vb.net 2008Express进行频谱分析应用程序，该应用程序将频谱图像绘制到picturebox中。我使用缓冲图形的速度和调用一个从画图事件的抽签例程。在大多数情况下，这是很好的工作，但当另一个窗口移动，当我回到我的窗口被覆盖的部分是空白的。我已经确定擦除是在从picturebox.paint事件调用抽签例程之后发生的。如果我再次调用绘图例程(在本例中是由Spectra_MouseUp引起的)，则图像将被完全重绘。

回到窗口后，我想不出如何保存(或重绘)整个图像。

我的代码的相关部分如下：

Private currentContext As BufferedGraphicsContext
Private spectraBuffer As BufferedGraphics

Private Sub DrawSpectra()
    Dim Gr As Graphics

    spectraBuffer = currentContext.Allocate(Spectra.CreateGraphics, Spectra.DisplayRectangle)
    Gr = spectraBuffer.Graphics
    '.
    '.
    '. Lots of drawing stuff here such as.... (yes, everything here is declared)
                If FillSpectra Then
                    Gr.DrawPolygon(BasePen, ptsSpec.ToArray)
                    Gr.FillPolygon(BaseBrush, ptsSpec.ToArray)
                Else
                    Gr.DrawLines(BasePen, ptsSpec.ToArray)
                End If
    '.
    '.
    ' Render the contents of the buffer to the Spectra window.
    spectraBuffer.Render()
End Sub

Private Sub frmMCAWindow_Activated(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles MyBase.Activated
    Call DrawSpectra()
    ' DrawSpectra() works fine from here
End Sub

Private Sub Spectra_MouseUp(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.MouseEventArgs) Handles Spectra.MouseUp
    Call DrawSpectra()
End Sub

Private Sub Spectra_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Spectra.Paint
    ' When dragging another window over mine, DrawSpectra() works fine here to keep the image in the picturebox 
    Debug.Print("Begin Spectra_Paint()")
    Call DrawSpectra()
    ' I put a 1 sec. sleep for testing, the image stayed complete while waiting
    ' The part that was covered was erased once the sleep completed.
    Debug.Print("End Spectra_Paint()")
End Sub

Answer 1

谢谢克里斯。结果是使用Spectra.CreateGraphics而不是PaintEventArgs (对于e.Graphics)才是问题所在。我重新做了下面的工作&它现在工作得很好。

Private currentContext As BufferedGraphicsContext
Private spectraBuffer As BufferedGraphics

Private Sub frmMCAWindow_Activated(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles MyBase.Activated
    Spectra.Invalidate()
End Sub

Private Sub Spectra_MouseUp(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.MouseEventArgs) Handles Spectra.MouseUp
    Spectra.Invalidate()
End Sub

Private Sub Spectra_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Spectra.Paint
    Dim Gr As Graphics

    spectraBuffer = currentContext.Allocate(e.Graphics, Spectra.DisplayRectangle)
    Gr = spectraBuffer.Graphics
    '.
    '.
    '. Lots of drawing stuff here such as....
            If FillSpectra Then
                Gr.DrawPolygon(BasePen, ptsSpec.ToArray)
                Gr.FillPolygon(BaseBrush, ptsSpec.ToArray)
            Else
                Gr.DrawLines(BasePen, ptsSpec.ToArray)
            End If
    '.
    '.
    ' Render the contents of the buffer to the Spectra window.
    spectraBuffer.Render()
End Sub