public Form1()
        {
            InitializeComponent();
        }
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (this.Visible==true)
            {
                e.Cancel = true;
                this.Visible = false;
            }
        }

        private void notifyIcon1_MouseClick(object sender, MouseEventArgs e)
        {
            if (e.Button==MouseButtons.Left)
            {
                if (this.Visible == false)
                {
                    this.Visible = true;
                    this.WindowState = FormWindowState.Normal;
                }
            }
        }

        private void 退出ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.Visible = false;
            Application.Exit();
        }

    static class Program
    {
        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
        [DllImport("user32.dll ", SetLastError = true)]
        static extern void SwitchToThisWindow(IntPtr hWnd, bool fAltTab);

        [DllImport("user32.dll", EntryPoint = "ShowWindow", CharSet = CharSet.Auto)]
        public static extern int ShowWindow(IntPtr hwnd, int nCmdShow);
        public const int SW_RESTORE=9;
        public static IntPtr formhwnd;
        static Form1 form = null;
        ///<summary>
        /// 应用程序的主入口点。
        ///</summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            string proc = Process.GetCurrentProcess().ProcessName;
            Process[] processes = Process.GetProcessesByName(proc);
            if (processes.Length <= 1)
            {
                form = new Form1();
                Application.Run(form);
            }
            else
            {
                for (int i = 0; i < processes.Length; i++)
                {
                    if (processes[i].Id != Process.GetCurrentProcess().Id)
                    {
                        if (processes[i].MainWindowHandle.ToInt32() == 0)
                        {
                            formhwnd = FindWindow(null, "Form1");
                            ShowWindow(formhwnd,SW_RESTORE);
                            SwitchToThisWindow(formhwnd, true);
                        }
                        else
                        {
                            SwitchToThisWindow(processes[i].MainWindowHandle, true);
                        }
                    }

                }
            }

        }
    }

private static Process RunningInstance()
{
Process current = Process.GetCurrentProcess();
Process[] processes = Process.GetProcessesByName(current.ProcessName);
//遍历正在有相同名字运行的例程 
foreach (Process process in processes)
{
//忽略现有的例程 
if (process.Id != current.Id)
{
//确保例程从EXE文件运行 
//if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
if (process.MainModule.FileName == current.MainModule.FileName)
{
//返回另一个例程实例 
return process;
}
}
}
//没有其它的例程，返回Null 
return null;
}
/// <summary>
/// 窗体焦点
/// </summary>
/// <param name="hWnd"></param>
/// <param name="fAltTab"></param>
[DllImport("user32.dll ", SetLastError = true)]
private static extern void SwitchToThisWindow(IntPtr hWnd, bool fAltTab);
/// <summary>
/// 显示窗体,同 ShowWindowAsync 差不多
/// </summary>
/// <param name="hwnd"></param>
/// <param name="nCmdShow"></param>
/// <returns></returns>
[DllImport("user32.dll", EntryPoint = "ShowWindow", CharSet = CharSet.Auto)]
private static extern int ShowWindow(IntPtr hwnd, int nCmdShow);
private const int SW_RESTORE = 9;
/// <summary>
/// 枚举窗体
/// </summary>
/// <param name="x"></param>
/// <param name="y"></param>
/// <returns></returns>
[DllImport("user32")]
private static extern int EnumWindows(CallBack x, int y);
private delegate bool CallBack(IntPtr hwnd, int lParam);
/// <summary>
/// 根据窗体句柄获得其进程ID
/// </summary>
/// <param name="hwnd"></param>
/// <param name="ID"></param>
/// <returns></returns>
[DllImport("User32.dll", CharSet = CharSet.Auto)]
private static extern int GetWindowThreadProcessId(IntPtr hwnd, out int ID);
/// <summary>
/// 根据窗体句柄获得窗体标题
/// </summary>
/// <param name="hWnd"></param>
/// <param name="lpText"></param>
/// <param name="nCount"></param>
/// <returns></returns>
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpText, int nCount);
/// <summary> 
/// 根据进程，显示其主窗体
/// </summary> 
private static void HandleRunningInstance(Process instance)
{
ShowWindow(instance.MainWindowHandle, SW_RESTORE);
SwitchToThisWindow(instance.MainWindowHandle, true); 
}
private static bool Report(IntPtr hwnd, int lParam)
{
//获得窗体标题
StringBuilder sb = new StringBuilder(50);
GetWindowText(hwnd, sb, sb.Capacity);
int calcID;
//获取进程ID 
GetWindowThreadProcessId(hwnd, out calcID);
if ((sb.ToString() == formName) && (pro != null) && (calcID == pro.Id)) //标题栏、进程id符合
{ 
ShowWindow(hwnd, SW_RESTORE);
SwitchToThisWindow(hwnd, true); 
return true;
}
else
return true;

}
private static string formName = string.Empty;
private static Process pro = null;
public static void Singling(string str)
{
formName = str;
Process instance = RunningInstance();
if (instance != null) //首先确定有无进程
{
pro = instance;
if (pro.MainWindowHandle.ToInt32() != 0) //是否托盘化
{
HandleRunningInstance(pro);
}
else
{
// System.Windows.Forms.MessageBox.Show("程序已运行!\n\r请查看托盘图标!"); 
CallBack myCallBack = new CallBack(Report);
EnumWindows(myCallBack, 0); 
}
System.Environment.Exit(System.Environment.ExitCode);

}
}