连续截图

void UpdateScreen(object state, EventArgs e) {
    lock (lockObject) {
        if (string.IsNullOrEmpty(textBox1.Text) && string.IsNullOrEmpty(textBox2.Text)) {
            btnStartCapture.Text = "开始截图";
            timer.Tick -= new EventHandler(UpdateScreen);
            BtnStartCapture_Flag = !BtnStartCapture_Flag;
            MessageBox.Show("未选择截图方式", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }
         
        if (isHandleMode){
            RECT rect2;
            GetWindowRect(hWnd, out rect2);
            int width = rect2.Right - rect2.Left;
            int height = rect2.Bottom - rect2.Top;
             
            IntPtr hdcWindow = GetWindowDC(hWnd);
            IntPtr hdcCompatible = CreateCompatibleDC(hdcWindow);
            IntPtr hBitmap = CreateCompatibleBitmap(hdcWindow, width, height);
 
            SelectObject(hdcCompatible, hBitmap);
            BitBlt(hdcCompatible, 0, 0, width, height, hdcWindow, 0, 0, 0x00CC0020); // CAPTUREBLT flag to capture layered windows
 
            img = Image.FromHbitmap(hBitmap);
 
            if (picBox.InvokeRequired) {
                picBox.Invoke((MethodInvoker)delegate {
                    picBox.Image = img;
                });
            } else {
                picBox.Image = img;
            }
             
            DeleteObject(hBitmap);
            DeleteDC(hdcCompatible);
            DeleteDC(hdcWindow);
        } else {
            using (Graphics g = Graphics.FromImage(img)) {
                g.CopyFromScreen(Point.Empty, Point.Empty, img.Size);
            }
 
            if (picBox.InvokeRequired) {
                picBox.Invoke((MethodInvoker)delegate {
                    picBox.Image = img;
                });
            } else {
                picBox.Image = img;
            }
        }
         
        filePath = string.Format("images/screenshot_{0}.{1}", captureCount, format);
        img.Save(filePath);
         
        if (captureCount == int.Parse(textBox4.Text)) {
            btnStartCapture.Text = "开始截图";
            timer.Tick -= new EventHandler(UpdateScreen);
            BtnStartCapture_Flag = !BtnStartCapture_Flag;
            MessageBox.Show("已完成", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
        captureCount++;
    }
}