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Single Instance Application...

Robin J Giltner — Sat, 26 Nov 2011 09:31:46 GMT

When using Strataframe the required Startup Object is AppMain to that the database connections for the Business Objects can be established, and with that, you can't use the Visual Studio Option of Single Instance Application in the Application Properties. So I was wondering what was the best way of handling this manually.

I spent a few minutes reading through some ways people have done this online, but it seems to boil down to searching through the processes and finding one that matches your form's Title or something such. I ended writing a quick method that searches on the type of the form in the AppMain's InitApplication method.

Is this the best way to handle this ? Also this doesn't currently allow the same application to be run by multiple users on the same system, ie users over Terminal Services etc. I guess I would have to add another quick check for if the Owner of that Process is the current Application's process owner or some such.

I was just wanting to get some input from anyone who may have had to do this as well.

Thanks

Robin Giltner

RE: Single Instance Application...

Ivan George Borges — Sat, 26 Nov 2011 09:31:46 GMT

Yep, that is it.

I go a bit further on my applications since I have a Licensing control based on licenses per machine. So I create the Mutex under a Global state, this way I can count the number of instances running even on various Terminal Service sessions.

RE: Single Instance Application...

Rogerio Mauri — Sat, 26 Nov 2011 07:54:07 GMT

Hi Ivan...

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            //-- Evita mais de uma instância
            bool ok;
            Mutex loMutex = new Mutex(true, Application.ProductName + Application.ProductVersion, out ok);
            if (!ok)
            {
                MessageBox.Show("Aplicativo já está em execução");
                Application.Exit();
                return;
            }

            //-- Enable visual styles on the application
            Application.EnableVisualStyles();

            ...

            //-- Run the application
            StrataFrameApplication.RunApplication();

            //-- Stop the session monitoring before the application exits to remove the low-level event handlers
            SessionLock.StopSessionMonitoring();

            GC.KeepAlive(loMutex);

        }

RE: Single Instance Application...

Ivan George Borges — Fri, 25 Nov 2011 09:06:25 GMT

Hi Rogerio.

GetProcessByName is a lot simpler, but has some disavantages:

it will allow 2 instances to run if you change the .EXE name
if you have 2 separate applications with the same name, it won't allow them to run at the same time
Mutex can work with a Global escope, so it will make sure the application run only once in the entire system, even on Terminal Services
apparently, GetProcessByName may not access minimized windows properly

RE: Single Instance Application...

Rogerio Mauri — Fri, 25 Nov 2011 08:38:49 GMT

Code...

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            //-- Evita mais de uma instância
            if (Process.GetProcessesByName(Process.GetCurrentProcess().ProcessName).Length > 1)
            {
                MessageBox.Show("Aplicativo já está em execução");
                Application.Exit();
                return;
            }

            //-- Enable visual styles on the application
            Application.EnableVisualStyles();

            //-- Add event handlers for the application events
            StrataFrameApplication.ShowGateway +=
                new StrataFrameApplication.ShowGatewayEventHandler(
                ShowGateway);

            ...

        }

RE: Single Instance Application...

Edhy Rijo — Fri, 06 Nov 2009 11:49:27 GMT

Hi Larry,

Thanks for the information. I google this issue and found some different approaches, I combined two of them and was able to put together a solution that will will do just what is expected from the user: if the application is minimized, it will just bring it to the from.

Of course this solution is not as simple as using the Mutex and may have other issues since it uses the System.Diagnostics.Process to get to the application.

Ok here is the code.. Copy these 2 classes to a new class file in the main project I called mine "SingleInstance.vb" or if you have a based class in the main .exe project you could use that as well.
[codesnippet]
#Region " Code to handle a single instance of the application "

'Windows API
Declare Function OpenIcon Lib "user32" (ByVal hwnd As Long) As Long
Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As Long) As Long

'''

''' Function to check and see if an instance of the application is already open
'''

''' Name of the application
''' True/False
'''
Public Shared Function IsAlreadyOpen(ByVal sApp As String) As Boolean
'Check running processes to see if application is already running
Dim pProcess As Process() = System.Diagnostics.Process.GetProcessesByName(sApp)
If pProcess.Length > 1 Then 'If > 1 then its already running
Return True
Else 'Not running
Return False
End If
End Function

Public Shared Sub ActivatePrevInstance(ByVal argStrAppToFind As String)
Dim PrevHndl As Long
Dim result As Long

Dim objProcess As New Process 'Variable to hold individual Process
Dim objProcesses() As Process 'Collection of all the Processes running on local machine
objProcesses = Process.GetProcesses() ''Get all processes into the collection

For Each objProcess In objProcesses

If UCase(objProcess.ProcessName) = UCase(argStrAppToFind) Then
If Not String.IsNullOrEmpty(objProcess.MainWindowTitle) Then
'MessageBox.Show(objProcess.MainWindowTitle)
PrevHndl = objProcess.MainWindowHandle.ToInt32()
Exit For
End If
End If
Next
If PrevHndl = 0 Then Exit Sub 'if No previous instance found exit the application.
''If found
result = OpenIcon(PrevHndl) 'Restore the program.
result = SetForegroundWindow(PrevHndl) 'Activate the application.

End 'End the current instance of the application.
End Sub
#End Region
[/codesnippet]

Now like in your case, to execute it in the AppMain.vb after the "Public Shared Sub Main()" add this code:
[codesnippet]
If SingleInstance.IsAlreadyOpen(My.Application.Info.ProductName) Then
SingleInstance.ActivatePrevInstance(My.Application.Info.ProductName)
Exit Sub
End If
[/codesnippet]

RE: Single Instance Application...

Larry Caylor — Fri, 06 Nov 2009 10:40:44 GMT

What I actually ended up doing in my applications is to display a SF message telling the user that an instance was already running. I imagine there is probably some way to display the original instance but our users are fine with the message so that's where I left it.

-Larry

RE: Single Instance Application...

Edhy Rijo — Thu, 05 Nov 2009 15:19:18 GMT

Hi Larry,

I also implemented your code and it does works well.

Instead of just exiting without letting the user know what may be happening, is there a way to simply show up the instance that is currently open?

RE: Single Instance Application...

Ivan George Borges — Mon, 10 Dec 2007 12:24:30 GMT

Hi Larry.

Thanks for the code snippet. I was just trying to accomplish this, and it worked really fine.

:smooooth:

RE: Single Instance Application...

StrataFrame Team — Mon, 10 Dec 2007 08:40:56 GMT

Haha, yep, Larry, much simpler. Good idea.

RE: Single Instance Application...

Larry Caylor — Fri, 07 Dec 2007 10:33:07 GMT

Robin,

I've been using the mutex method for restricting an application to a single instance. It's easy to implement and so far it's worked well for me. By varying the safeName you should be able to over come the problem in Terminal Services.

I include the following code at the top of Public Shared Sub Main in AppMain.

Dim firstInstance As Boolean = False
'-- Create a name based on the user application path.
Dim safeName As String = Application.UserAppDataPath.Replace("\", "_")
Dim myMutex As Mutex = New Mutex(True, safeName, firstInstance)
'-- Bail if not first instance.
If Not (firstInstance) Then Exit Sub
'-- Make sure the program holds the mutex as long as it is running.
GC.KeepAlive(myMutex)

See http://www.ai.uga.edu/mc/SingleInstance.html for more info.

-Larry

RE: Single Instance Application...

Robin J Giltner — Fri, 07 Dec 2007 10:30:44 GMT

Thanks Ben. I'll start looking through that for a good starting point at least.

Robin Giltner

RE: Single Instance Application...

StrataFrame Team — Fri, 07 Dec 2007 09:01:17 GMT

It's complicated, but not impossible. You might want to duplicate what .NET does with the IsSingleInstance property of the Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase class. I opened the Microsoft.VisualBasic.dll with Reflector and looked at the Run() method. The first thing it checks on is the IsSingleInstance property. If it's a single instance, then it checks the application instance ID through some stuff and makes sure there's not already one running in memory. So, it would be pretty simple to just copy the code out of Reflector and add it to your application.