没有打开时，就打开一个；如果打开了，再次双击exe后，已打开的窗体就前置；如果窗体已经打开并最小化，就还原窗体并前置！

windowns窗体应用项目：

  1.         //以下所有代码放在窗体的Program.cs里面
  2.         [DllImport("user32.dll")]
  3.         private static extern bool SetForegroundWindow(IntPtr hWnd);
  4.         [DllImport("user32.dll")]
  5.         private static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);
  6.         [DllImport("user32.dll")]
  7.         private static extern bool IsIconic(IntPtr hWnd);
  8.         private const int SW_RESTORE = 9;
  9.         /// <summary>
  10.         /// c# 进程窗口显示并前置
  11.         /// </summary>
  12.         public static void RaiseOtherProcess()
  13.         {
  14.             Process proc = Process.GetCurrentProcess();
  15.             Process.GetProcesses();
  16.             foreach (Process otherProc in Process.GetProcessesByName(proc.ProcessName))
  17.             {
  18.                 //ignore "this" process
  19.                 if (proc.Id != otherProc.Id)
  20.                 {
  21.                     // Found a "same named process".
  22.                     // Assume it is the one we want brought to the foreground.
  23.                     // Use the Win32 API to bring it to the foreground.
  24.                     IntPtr hWnd = otherProc.MainWindowHandle;
  25.                     if (IsIconic(hWnd))
  26.                     {
  27.                         ShowWindowAsync(hWnd, 9);
  28.                     }
  29.                     SetForegroundWindow(hWnd);
  30.                     break;
  31.                 }
  32.             }
  33.         }
  35.         static void Main()
  36.         {
  37.             Application.EnableVisualStyles();
  38.             Application.SetCompatibleTextRenderingDefault(false);
  39.             bool createdNew = new bool();
  40.             Mutex instance = new Mutex(true, "Regfrm", out createdNew);
  41.             if (createdNew)
  42.             {
  43.                 Application.Run(new Regfrm());
  44.                 instance.ReleaseMutex();
  45.                 //如果需要窗体重启，并出现问题，将这句改为
  46.                 //instance.Dispose();
  47.             }
  48.             else
  49.             {
  50.                 RaiseOtherProcess();
  51.                 Application.Exit();
  52.             }
  53.         }

=====================================

windowns窗体应用插件项目：

  1.         public Form frm;//这一句放在class里面
  3.         private void Button1_Click(object sender, RibbonControlEventArgs e)
  4.         {
  5.             //以下代码放在插件控件的事件里面
  6.             if (frm == null || frm.IsDisposed)
  7.             {
  8.                frm = new Mainfrm();
  9.                frm.Show();
  10.             }
  11.             else
  12.             {
  13.                 if (frm.WindowState == FormWindowState.Minimized)
  14.                 {
  15.                     frm.WindowState = FormWindowState.Normal;
  16.                 }
  17.                 frm.Activate();
  18.             }
  19.             //以上代码放在插件控件的事件里面
  20.         }