StrataFrame Forum

Single Instance Application...

http://forum.strataframe.net/Topic12923.aspx

By Robin J Giltner - 12/6/2007

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
By StrataFrame Team - 12/7/2007

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.
By Robin J Giltner - 12/7/2007

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

Robin Giltner

By Larry Caylor - 12/7/2007

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
By StrataFrame Team - 12/10/2007

Haha, yep, Larry, much simpler.  Good idea.
By Ivan George Borges - 12/10/2007

Hi Larry.

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

Smooooth

By Edhy Rijo - 11/5/2009

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?
By Larry Caylor - 11/6/2009

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

By Edhy Rijo - 11/6/2009

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.



#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





Now like in your case, to execute it in the AppMain.vb after the "Public Shared Sub Main()" add this code:



If SingleInstance.IsAlreadyOpen(My.Application.Info.ProductName) Then

SingleInstance.ActivatePrevInstance(My.Application.Info.ProductName)

Exit Sub

End If
By Rogerio Mauri - 11/25/2011

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);

            ...

        }

 

By Ivan George Borges - 11/25/2011

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
By Rogerio Mauri - 11/26/2011

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);


        }

By Ivan George Borges - 11/26/2011

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.