private void snappic()
        {
            UInt32 li = GetWindowHwndByText("计算器");
            if (li == 0) return;
            RECT r;
            GetWindowRect(li, out  r);
            Bitmap bitmap = new Bitmap(r.Right - r.Left, r.Bottom - r.Top);
            Graphics g = Graphics.FromImage(bitmap);
            bool a = PrintWindow(li, g.GetHdc(), 0);
            g.ReleaseHdc();
            pictureBox1.Image = bitmap;
        }