[RESOLVED] Starting program in already started instance

Hello everyone.

I was wondering how to PROPERLY make a multi-tabbed or multi-window application that can handle file start requests.

For example, on startup my "Desktop Application" runs and sits there waiting for a task, either through the main menu, or for a file to display in a window. Now the problem is simple, how can I make this already running program load the dropped file (dropped on the executable (!)), instead of starting a new instance.

I understand I will have to check if the process is running, and if so, do some stuff with it. But the problem is passing the message to the active program.

Previously I used text files with paths/arguments in them, but I don't like the idea of the OS/program checking every 500 ms if a file is created in the "load this" folder...

Then I thought of sending a message using "Send Message", for example changing the text in a textbox and handle the "Text Changed" event, but is this reliable? Can any other program interfere with it?

So, basically I need the proper way of doing all of this. For example, Microsoft Visual Studio does this nicely, and no lag whatsoever...

1) Make sure you are using the application framework (My Project -> Properties -> Application tab)

2) Make sure "Make single instance application" is checked.

3) Click "View Application Events" to generate the ApplicationEvents.vb file.

4) In that generated file, select "(My Application Events)" from the left combo box, and then "StartupNextInstance" from the combo box on the right to generate a handler that will be fired in your first instance of the application when a second instance is attempted to be started. The StartupNextInstanceEventArgs has a "CommandLine" property - if you drag a file onto the executable, the first string in this property will be the filename of the dropped file.

5) If you are making a multi-window single-instance app (i.e. each "new" instance gets its own window) you should go back to orject properties and set the "Shutdown mode" to be "When last form closes", otherwise closing the "first instance"'s form will exit the app closing all the "instances".

Ah, cool. Never knew this existed. ;)

Code:

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Namespace My
    Partial Friend Class MyApplication
        Private Sub MyApplication_StartupNextInstance(ByVal sender As Object, ByVal e As Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs) Handles Me.StartupNextInstance
            For Each cmd As String In e.CommandLine
                MsgBox(cmd)
            Next
        End Sub
    End Class
End Namespace

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Thanks Evil_Giraffe :thumb: