Single instance on Windows/Desktop/Mac?

[TopperDEL]

Is there a central way to assure that only one instance of my app is open at all times on Windows, Desktop and Mac? Any recommendations?

[jeromelaban]

Thanks for the question. At this time, there's no common API to ensure that, but you can use named Mutex to detect already running instances.

[TopperDEL]

You are right! I tried this before but it did not work for whatever reason. Now it did.

For anyone curious, here is my solution:

public App()
{
    this.InitializeComponent();

    if (!EnsureSingleInstance())
    {
        BringExistingInstanceToFront();

        // If another instance is already running, exit this one
        Environment.Exit(0);
    }
}

#region Single-Instance
private static bool EnsureSingleInstance()
{
    string appName = "MyApp";

    if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
    {
        // Windows: Use a named Mutex
        _mutex = new Mutex(true, $"Global\\{appName}", out bool isNewInstance);
        return isNewInstance;
    }
    else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
    {
        // macOS: Workaround - Use a file lock
        return EnsureSingleInstanceMac(appName);
    }
    else
    {
        // Other platforms: Assume single instance is not needed
        return true;
    }
}

private static bool EnsureSingleInstanceMac(string appName)
{
    string lockFilePath = Path.Combine(Path.GetTempPath(), appName + ".lock");

    try
    {
        // Try to create the lock file
        if (File.Exists(lockFilePath))
        {
            // Check if another process is holding the lock
            var existingProcess = Process.GetProcessesByName("MyApp").FirstOrDefault();
            if (existingProcess != null && existingProcess.Id != Process.GetCurrentProcess().Id)
            {
                return false;
            }
        }

        // Create a lock file to indicate this instance is running
        File.WriteAllText(lockFilePath, Process.GetCurrentProcess().Id.ToString());
        return true;
    }
    catch
    {
        return false;
    }
}

[DllImport("user32.dll")]
private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

[DllImport("user32.dll")]
private static extern bool SetForegroundWindow(IntPtr hWnd);

private static void BringExistingInstanceToFront()
{
    IntPtr hWnd = FindWindow(null, "MyApp Title");
    if (hWnd != IntPtr.Zero)
    {
        SetForegroundWindow(hWnd);
    }
}
#endregion