GDI 对象不删除

Question

我被要求通过将屏幕截图保存到 BMP 来调试一些试图在 VB.Net 中制作图形电影的代码。我发现它在达到 10,000 个 GDI 对象的限制后失败，并确定泄漏来自此代码：

Dim r As Integer
Dim hdcdest As System.IntPtr = CType(CreateCompatibleDC(CInt(GetWindowDC(frmDynamicsMDI.MainControl.fraAnimation.Handle))), IntPtr)
Dim hdcbitmap As System.IntPtr = CType(CreateCompatibleBitmap(GetWindowDC(frmDynamicsMDI.MainControl.fraAnimation.Handle), _
                                                            frmDynamicsMDI.MainControl.fraAnimation.Size.Width - (0 + CropRight), _
                                                            frmDynamicsMDI.MainControl.fraAnimation.Size.Height - (10 + 0)), IntPtr)
SelectObject(hdcdest, CInt(hdcbitmap))
BitBlt(hdcdest, 0, 0, frmDynamicsMDI.MainControl.fraAnimation.Width - (0 + CropRight), frmDynamicsMDI.MainControl.fraAnimation.Height - (10 + 0), _
GetWindowDC(frmDynamicsMDI.MainControl.fraAnimation.Handle), 0, 10, 13369376)

Image = System.Drawing.Image.FromHbitmap(hdcbitmap)

r = DeleteDC(CInt(GetWindowDC(frmDynamicsMDI.MainControl.fraAnimation.Handle)))


DeleteObject(CInt(hdcdest))
DeleteObject(CInt(hdcbitmap))

BitBlt 声明为：

Private Declare Function BitBlt Lib "GDI32" (ByVal hdestDC As IntPtr, ByVal x As Integer, ByVal y As Integer, _
        ByVal nwidth As Integer, ByVal nheight As Integer, ByVal HsrcDC As IntPtr, ByVal xsrc As Integer, ByVal ysrc As Integer, ByVal _
        dwRop As Int32) As Boolean

2 个System.IntPtr 创建调用每个创建 2 个 GDI 对象，而“BitBlt”创建 1 个。我发现的问题是 DeleteObject() 调用每个只删除 1 个 GDI 对象。

那么删除调用是否执行不正确？或者是否有其他对象与未被删除的 GDI 对象一起浮动？

Answer 1

来自GetWindowDC function

GetWindowDC 用于在窗口的非客户区内实现特殊的绘画效果。不建议在任何窗口的非客户区绘画。

绘制完成后，必须调用ReleaseDC函数来释放设备上下文。不释放窗口设备上下文会严重影响应用程序请求的绘制。

您的代码在多个地方调用 GetWindowDC。尝试只在变量中调用一次，然后在完成后对其使用 ReleaseDC。