c# winform实现截图并保持图片功能

       最近项目需要对界面进行截图并保存的功能，在网上搜索了下结合实际需求最终完成功能，代码如下

　　　//调用导图

　　　private void pictureBox4_Click(object sender, EventArgs e)
        {

            Bitmap bitmap = new Bitmap(this.Width, this.Height);
            DrawToBitmap(this, bitmap, new Rectangle(0, 0, this.Width, this.Height));

            bool isSave = true;
            SaveFileDialog saveImageDialog = new SaveFileDialog();
            saveImageDialog.Title = "图片保存";
            saveImageDialog.Filter = @"jpeg|*.jpg|bmp|*.bmp|gif|*.gif";
            if (saveImageDialog.ShowDialog() == DialogResult.OK)
            {
                string fileName = saveImageDialog.FileName.ToString();
                if (fileName != "" && fileName != null)
                {
                    string fileExtName = fileName.Substring(fileName.LastIndexOf(".") + 1).ToString();
                    System.Drawing.Imaging.ImageFormat imgformat = null;
                    if (fileExtName != "")
                    {
                        switch (fileExtName)
                        {
                            case "jpg":
                                imgformat = System.Drawing.Imaging.ImageFormat.Jpeg;
                                break;
                            case "bmp":
                                imgformat = System.Drawing.Imaging.ImageFormat.Bmp;
                                break;
                            case "gif":
                                imgformat = System.Drawing.Imaging.ImageFormat.Gif;
                                break;
                            default:
                                MessageBox.Show("只能存取为: jpg,bmp,gif 格式");
                                isSave = false;
                                break;
                        }

                    }
                    //默认保存为JPG格式  
                    if (imgformat == null)
                    {
                        imgformat = System.Drawing.Imaging.ImageFormat.Jpeg;
                    }
                    if (isSave)
                    {
                        try
                        {
                            images.Save(fileName, imgformat);
                            //MessageBox.Show("图片已经成功保存!");  
                        }
                        catch
                        {
                            MessageBox.Show("保存失败,你还没有截取过图片或已经清空图片!");
                        }
                    }
                }
            }

        }

 　　 [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern int SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr SendMessage(HandleRef hWnd, int msg, IntPtr wParam, IntPtr lParam);

        [DllImport("gdi32.dll", CharSet = CharSet.Auto, SetLastError = true, ExactSpelling = true)]
        public static extern bool BitBlt(HandleRef hDC, int x, int y, int nWidth, int nHeight, HandleRef hSrcDC, int xSrc, int ySrc, int dwRop);

        /// <summary>
        /// 支持呈现到指定的位图。
        /// </summary>
        public static Bitmap DrawToBitmap(Control control, Bitmap bitmap, Rectangle targetBounds)
        {
            if (bitmap == null)
            {
                throw new ArgumentNullException("bitmap");
            }
            if (((targetBounds.Width <= 0) || (targetBounds.Height <= 0)) || ((targetBounds.X < 0) || (targetBounds.Y < 0)))
            {
                throw new ArgumentException("targetBounds");
            }
            Bitmap image = new Bitmap(control.Width, control.Height, bitmap.PixelFormat);
            using (Graphics graphics = Graphics.FromImage(image))
            {
                IntPtr hdc = graphics.GetHdc();
                SendMessage(new HandleRef(control, control.Handle), 0x317, hdc, (IntPtr)30);
                using (Graphics graphics2 = Graphics.FromImage(bitmap))
                {
                    IntPtr handle = graphics2.GetHdc();
                    BitBlt(new HandleRef(graphics2, handle), 0, 0, control.Width, control.Height, new HandleRef(graphics, hdc), targetBounds.X, targetBounds.Y,

0xcc0020);
                    graphics2.ReleaseHdcInternal(handle);
                }
                graphics.ReleaseHdcInternal(hdc);
            }
            return image;
        }