Credit: Chris Tacke

		private const int ERROR_ALREADY_EXISTS = 183;

		[DllImport("coredll.dll", EntryPoint="GetLastError")]
		private static extern int GetLastError();

		[DllImport("coredll.dll", EntryPoint="CreateMutexW")]
		private static extern int CreateMutex(IntPtr lpMutexAttributes, bool InitialOwner, string MutexName);		

		public static bool IsInstanceRunning()
		{	

			string appname = System.Reflection.Assembly.GetExecutingAssembly().GetName().Name;
			
			if(CreateMutex(IntPtr.Zero, true, appname) != 0)
			{
				if(GetLastError() == ERROR_ALREADY_EXISTS)
				{
					DEBUGMSG(true, "Already running\r\n");
					return true;
				}
				else
				{
					DEBUGMSG(true, "Not already running\r\n");
					return false;
				}
			}

			DEBUGMSG(true, "CreateMutex failed!\r\n");
			return false;
		}

Do you know how to set focus to instance running ??

quote:

---

Do you know how to set focus to instance running ??

---

This should get you started (it uses PInvoke and FindWindow/IsIconic/ShowWindow/SetForegroundWindow API calls):

using System.Threading;
...
[STAThread]
static void Main()
{
//allow only one instance
bool ownsmutex;

Mutex m = new Mutex(true, Application.ProductName, out ownsmutex);
if (!ownsmutex)
{
//bring old instance to the front
IntPtr hwnd = Win32.API.FindWindow(null, "MainFormTitle");
if (hwnd != IntPtr.Zero)
{
if (Win32.API.IsIconic(hwnd))
Win32.API.ShowWindow(hwnd, Win32.API.ShowState.SW_SHOWNOACTIVATE);
Win32.API.SetForegroundWindow(hwnd);
}

//exit this application
Environment.Exit(0);
return;
}
Application.Run(new MainForm());
}


If you need the PInvoke code (in my Win32.API namespace), email me privately at stormfire@@@bigfoot.com.
ShaneB

My apologies if this is a compact framework discussion...

I thought the question was regarding desktop versions of Windows and I posted a bit too hastily.

ShaneB

Assuming that this thread refers to the Compact Framework, it is no longer neccessary to check for previous app instances. The CF does it for us. If there is already an instance of an application running when the user selects the app from the Start menu, the CF will use the currently running instance instead of spawning a new instance.
[:)]

Dave Ranck

Actually that's not 100% true. For PocketPC it is, but CE 4.x still requires that you look for an existing instance yourself.

Here is the VB.Net implementation:
<code>
Public Class PrevInstance
Const ERROR_ALREADY_EXISTS As Integer = 183

<System.Runtime.InteropServices.DllImport("coredll.dll", EntryPoint:="GetLastError")> _
Private Shared Function GetLastError() As Integer
End Function

<System.Runtime.InteropServices.DllImport("coredll.dll", EntryPoint:="CreateMutexW")> _
Private Shared Function CreateMutex(ByVal lpMutexAttributes As IntPtr, ByVal InitialOwner As Boolean, ByVal MutexName As String) As Integer
End Function

Public Shared Function IsInstanceRunning() As Boolean
Try
Dim appname As String = System.Reflection.Assembly.GetExecutingAssembly().GetName().Name
If CreateMutex(IntPtr.Zero, True, appname) <> 0 Then
If GetLastError() = ERROR_ALREADY_EXISTS Then
Return True
Else
Return False
End If
End If
Return False
Catch ex As Exception
MsgBox("IsInstanceRunning Error: " & ex.ToString)
End Try
End Function 'IsInstanceRunning
End Class
</code>

Scott

Here's my suggestion:

	public frmMain()
	{
		try
		{

			SocketListener.Bind(new IPEndPoint(IPAddress.Loopback, 1033));	
			InitializeComponent();			
		}
		catch
		{
			Application.Exit();
		}		
	}

only one app can hear at one port. is there an app listening at port x, so your app runs at 2nd start into an error.

~~~~~~~~~~

no code no food