How to create single instance WPF Application that restores the open window when an attempt is made to open another instance?

Question

Sorry it the title is hard to understand. I wasn\'t sure how to word it.

I have an application that should only be allowed to run one instance per user session. If t

Answer 1

I removed the tag StartupUri from the App.xaml file.

Change the Build Action of App.xaml, from ApplicationDefinition to Page (You can change it on the property window).

Add a reference to Microsoft.VisualBasic (namespace to WindowsFormsApplicationBase).

On the class App.xaml.cs, put this code:

public partial class App : Application
{
    App()
    {
        InitializeComponent();
    }

    [STAThread]
    static void Main()
    {
        SingleInstanceManager manager = new SingleInstanceManager();
        manager.Run(new[] {"teste"});
    }
}

public class SingleInstanceManager : WindowsFormsApplicationBase
{
    SingleInstanceApplication app;

    public SingleInstanceManager()
    {
        this.IsSingleInstance = true;
    }

    protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
    {
        // First time app is launched
        app = new SingleInstanceApplication();
        app.Run();
        return false;
    }

    protected override void OnStartupNextInstance(StartupNextInstanceEventArgs eventArgs)
    {
        // Subsequent launches
        base.OnStartupNextInstance(eventArgs);
        app.Activate();
    }
}

public class SingleInstanceApplication : Application
{
    protected override void OnStartup(System.Windows.StartupEventArgs e)
    {
        base.OnStartup(e);

        // Create and show the application's main window
        MainWindow window = new MainWindow();
        window.Show();
    }

    public void Activate()
    {
        // Reactivate application's main window

        this.MainWindow.WindowState = WindowState.Normal;
        this.MainWindow.Activate();
    }
}

I hope it helps :D