case 1:

                        CaptureScreen.GetDesktopImage().Save(this.saveFileDialog1.FileName,

                            System.Drawing.Imaging.ImageFormat.Jpeg);

                        break;

                    case 2:

                        CaptureScreen.GetDesktopImage().Save(this.saveFileDialog1.FileName,

                            System.Drawing.Imaging.ImageFormat.Gif);

                        break;

                    case 3:

                        CaptureScreen.GetDesktopImage().Save(this.saveFileDialog1.FileName,

                            System.Drawing.Imaging.ImageFormat.Bmp);

                        break;

                    case 4:

                        CaptureScreen.GetDesktopImage().Save(this.saveFileDialog1.FileName,

                            System.Drawing.Imaging.ImageFormat.Tiff);

                        break;

                }

                PlatformInvokeUSER32.ShowWindow(Form.ActiveForm.Handle,4);

            }

        }

4 实现代码

using System;

using System.Drawing;

using System.Runtime.InteropServices;

namespace WindowsApplication3

{

    // <summary>

    // Plateform 的摘要说明。

    // </summary>

    public class PlatformInvokeGDI32

    {

        #region Class Variables

        public  const int SRCCOPY = 13369376;

        #endregion

        #region Class Functions

        [DllImport("gdi32.dll",EntryPoint="DeleteDC")]

        public static extern IntPtr DeleteDC(IntPtr hDc);

        [DllImport("gdi32.dll",EntryPoint="DeleteObject")]

        public static extern IntPtr DeleteObject(IntPtr hDc);