bool bOnlyOneInstance = false;
                System.Threading.Mutex mutex = new System.Threading.Mutex(true, Application.UserAppDataPath.Replace(@"\", "_"), out bOnlyOneInstance);

                if (!bOnlyOneInstance)
                {
                    MessageBox.Show("系统已经运行!", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    System.Environment.Exit(0);
                    return;
                }

------解决方案--------------------

判断的方法
C# code
/// <summary>
        /// 判断系统是否已打开
        /// </summary>
        /// <returns></returns>
        private bool IsExistCurrentProcess()
        {
            bool functionReturnValue = false;
            bool bTemp = false;
            try
            {
                string assemblyName = Assembly.GetExecutingAssembly().GetName().Name;
                Process current = Process.GetCurrentProcess();
                Process[] processes = Process.GetProcessesByName(assemblyName);
                foreach (Process pro in processes)
                {
                    if (current.Id != pro.Id)
                    {
                        bTemp = true;
                        break; // TODO: might not be correct. Was : Exit For
                    }
                }
                functionReturnValue = bTemp;
            }
            catch
            {
                functionReturnValue = bTemp;
            }
            return functionReturnValue;
        }

------解决方案--------------------
用放射查找 你知道它的名字吧

------解决方案--------------------

是否运行可以遍历进行表，也可以用windows的api: FindWindow(null,"你程序的窗体名称") ;
[DllImport("user32.dll")]
private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

如果程序窗口存在，它返回窗口的句柄。

显示窗口的windows api showWindow(Findwindow找到的窗口句柄,5);
[DllImport("user32.dll")]
private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
第二个参数nCmdShow：
#define SW_HIDE             0
#define SW_SHOWNORMAL       1
#define SW_NORMAL           1
#define SW_SHOWMINIMIZED    2
#define SW_SHOWMAXIMIZED    3
#define SW_MAXIMIZE         3
#define SW_SHOWNOACTIVATE   4
#define SW_SHOW             5
#define SW_MINIMIZE         6
#define SW_SHOWMINNOACTIVE  7
#define SW_SHOWNA           8
#define SW_RESTORE          9
#define SW_SHOWDEFAULT      10
#define SW_FORCEMINIMIZE    11
#define SW_MAX              11



------解决方案--------------------
用反射,通过窗体的名字来反射窗体实例
探讨

引用:
if (IsExistCurrentProcess())
{
form.Visible = true;
form.WindowState = FormWindowState.Normal;
form.Show();
}

引用:
引用:
判断的方法

……


------解决方案--------------------
C# code
bool runone;
                System.Threading.Mutex run = new System.Threading.Mutex(true, "Frm", out runone);
                if (!runone)
                {
                    MessageBox.Show("程序已经运行,不能重复打开！", "提示", MessageBoxButtons.OK);
                    return;
                }

------解决方案--------------------
单例模式

打开A窗口  

  A a=A.GetInstance();
a.show();
  


A窗口中
       public static ManagerList form = null;