BitBlt问题部份黑屏的问题!

Question

  private static IntPtr CreateBitmap(IntPtr hWnd, int width, int height)
        {            Bitmap retVal = new Bitmap(width, height);            Graphics sGrap = Graphics.FromImage(retVal);            IntPtr hdc = sGrap.GetHdc();            if (WinApi.PrintWindow(hWnd, hdc, 0))
            {
                sGrap.ReleaseHdc(hdc);
            }
            else
            {
                throw new Exception("截取窗体图片出错");
            }            return hdc;
        }        private static Bitmap CreateBitmap(IntPtr shdc, int x, int y, int width, int height)
        {                    Bitmap retVal = new Bitmap(width, height);            Graphics dhcd = Graphics.FromImage(retVal);            IntPtr dPtr = dhcd.GetHdc();            if (WinApi.BitBlt(dPtr, 0, 0, width, height, shdc, x, y, WinApi.SRCCOPY) == 0)
            {
                throw new Exception("区域截图错误");
            }
            else
            {
                dhcd.ReleaseHdc(dPtr);
            }            return retVal;
        }//Api声明
 public const int SRCCOPY = 0xcc0020;
        [DllImport("gdi32.dll ")]
        public static extern int BitBlt(IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);        [DllImport("user32.dll")]        public static extern bool PrintWindow(        IntPtr hwnd, // Window to copy,Handle to the window that will be copied.         IntPtr hdcBlt, // HDC to print into,Handle to the device context.         UInt32 nFlags // Optional flags,Specifies the drawing options. It can be one of the following values.         );