Single Instance Windows Forms Application

On a previous post I talked about how to create a splash screen for a windows forms application. Now I will be demonstrating how to make a single instance application.

As in the other post I will be using the WindowsFormsApplicationBase class included with the .NET Framework. In order to use this class your application project must add a reference to Microsoft.VisualBasic library.

Having added the reference, the code needed is very simple:

using System;
using System.Linq;
using System.Windows.Forms;
using Microsoft.VisualBasic.ApplicationServices;

class SingleInstanceApp : WindowsFormsApplicationBase
{
    public SingleInstanceApp()
        : base()
    {
        this.IsSingleInstance = true;
    }

    protected override void OnStartupNextInstance(
        StartupNextInstanceEventArgs e)
    {
        base.OnStartupNextInstance(e);

        string[] secondInstanceArgumens = e.CommandLine.ToArray();

        // Handle command line arguments of second instance

        if (e.BringToForeground)
        {
            this.MainForm.BringToFront();
        }
    }

    protected override void OnCreateMainForm()
    {
        base.OnCreateMainForm();

        this.MainForm = new MainForm();
    }
}

static class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        new SingleInstanceApp().Run(Environment.GetCommandLineArgs());
    }
}

With this sample code you will have a single instance application that, if configured to do so, will bring itself to the foreground when the user tries to launch a second instance. More advanced scenarios such as handling the command line arguments of the second instance on the first instance are also supported.

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Splash Screen for Windows Forms Application

Splash screens are commonly used in Windows Forms applications as a way to give rapid feedback to the user while the rest of the application loads, more specifically, its main form.

Implementing the loading of other components in the background, specially UI related components, while at the same time displaying a splash screen is something easy to get wrong.

However, if you don’t mind adding a reference to Microsoft.VisualBasic, a simpler solution is available. Check example below.

using System;
using System.Windows.Forms;
using Microsoft.VisualBasic.ApplicationServices;

internal class ExampleApp : WindowsFormsApplicationBase
{
    protected override void OnCreateSplashScreen()
    {
        // Custom splash screen
        this.SplashScreen = new SplashScreen();
    }

    protected override void OnCreateMainForm()
    {
        // Time consuming startup operations go here

        // Application main form
        this.MainForm = new MainForm();
    }
}

internal static class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        var application = new ExampleApp();

        application.MinimumSplashScreenDisplayTime = 1500;
        application.Run(Environment.GetCommandLineArgs());
    }
}