Passing argument to another instance of the same application

Question

I'm having a seriously problem with my little application; basically it's very easy to understand:

My software, when opened, do it's things.

I want to focus to opening another instance (And I mean opening again the .exe) ,check if it's already opened. If not simply start the application but if it's already running (AKA second or more instance) "simply" pass input argument (the args string array)to the first instance, that will processate it adeguately.

Here's my program.cs

static class Program
{
    static Mutex mutex = new Mutex(true, "{blabla}");

    [STAThread]
    static void Main(String[] args)
    {
        if (mutex.WaitOne(TimeSpan.Zero, true))
        {
            //First Instance!

            try
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);

                CALL A MY STATIC METHOD, DO SOME THINGS

                Application.Run(new Form1());
            }
            finally
            {
                mutex.ReleaseMutex();
            }
        }
        else
        {
            //Not-so-first instance!
            CALL A STATIC METHOD, 
            DO OTHER THINGS LIKE COMUNICATE WITH FIRST INSTANCE

            SIMPLY CLOSE.
        }
    }
}

This will only recognize (with mutex) if it's already opened but (off course) it can't communicate anything to the main instance.

I've tried lot of things but I can't get it work.

I've tried this but I seriously don't understand (after a lot of time wasted) how to put my "first time" code and the "already running" code.

Tried also MSMQ but I can't make it work.

Can someone please help me? It's a basic software that do a very basic things but I've spent day to make it work like I want!

Answer 1

One of the simplest ways to communicate would be to send a Windows message from the second instance to the first instance. The second instance would use PostMessage to send the message and the first instance would override the WndProc method of Form1 to handle the message.

There is an example here: Send message to a Windows process (not its main window)

That question also has an answer that uses a pipe (and WCF) for the communication.

There are many forms of interprocess communication. Which one you use depends on your needs, for example Windows Messages can't carry a great deal of information whereas a pipe can stream data at very high speed.

Update A simple alternative could be IPCChannel . This allows you to create an object in the first instance that can be called by the second instance. You can create a method on that object and pass your data as arguments

Answer 2

Use Mutex.

    // Generate your GUID and put it here
    private const string ProgramRunningGuid = "BD2023EE-F7B3-47B8-8C76-32668196E4D3";
    private Mutex _mutex;

    private bool IsProgramRunning()
    {
        bool createdNew;
        // It returns a bool value determining if a Mutex that created is new
        // If the program is already running mutex wouldn't be new
        _mutex = new Mutex(true, ProgramRunningGuid, out createdNew);
        return !createdNew;
    }

On program exit you need to release the mutex:

    _needlesRunningMutex.ReleaseMutex();

And if you want to focus the already running instance of your application you can check my answer with working solution here: https://stackoverflow.com/a/35018042/3731444

If you just need to share some bool arguments to determine if things are turned on or off you can use Mutexes for each of them either.

If you need to pass parameters to your .exe when you're starting it check this question: How to pass parameters to an exe?

If you need to make a continious communication between two instances of your running apps keep it up with MSMQ. I'll try to help you if any questions.

Check a how to use MSMQ here: https://github.com/IvanYurchenko/MSMQSample

Answer 3

I pass the arguments through a text file (I'm sure you can translate from VB.NET/pseudocode):

Private _uniqueEventName As String
Private _uniqueMutexName As String
Private _eventWaitHandle As EventWaitHandle
Private _mutex As Mutex

Private Sub ensureSingleInstance()
    _uniqueEventName = "{0ae64101-e630-4221-bf10-123fdddd5ab2}" + Assembly.GetEntryAssembly().GetName().Name
    _uniqueMutexName = "{03169a07-793b-48c6-8ceb-1232388cb69a}" + Assembly.GetEntryAssembly().GetName().Name

    Dim isOwned As Boolean
    _mutex = New Mutex(True, _uniqueMutexName, isOwned)
    _eventWaitHandle = New EventWaitHandle(False, EventResetMode.AutoReset, _uniqueEventName)

    GC.KeepAlive(_mutex)

    If isOwned Then
        Dim thread As Thread = New Thread(
                               Sub()
                                   While _eventWaitHandle.WaitOne()
                                       Application.Dispatcher.BeginInvoke(
                                           Sub()
                                               ' ****************************************************
                                               ' READ AND PROCESS THE ARGUMENTS FROM C:\MYAPPARGS.TXT
                                               ' ****************************************************

                                               If Not Application.MainWindow Is Nothing Then
                                                   _loggingDAL.Log("Activating main window")

                                                   If (Application.MainWindow.WindowState = WindowState.Minimized Or Application.MainWindow.Visibility = Visibility.Hidden) Then
                                                       Application.MainWindow.Show()
                                                       Application.MainWindow.WindowState = WindowState.Normal
                                                   End If

                                                   Application.MainWindow.Activate()
                                                   Dim topMost As Boolean = Application.MainWindow.Topmost
                                                   Application.MainWindow.Topmost = True
                                                   Application.MainWindow.Topmost = topMost
                                                   Application.MainWindow.Focus()
                                               End If
                                           End Sub)
                                   End While
                               End Sub)
        thread.IsBackground = True
        thread.Start()
    Else
        _loggingDAL.Log("There is already an instance running -> switching and quitting")

        ' ***************************************
        ' WRITE THE ARGUMENTS TO C:\MYAPPARGS.TXT
        ' ***************************************

        _eventWaitHandle.Set()
        Application.Shutdown()
    End If
End Sub