Partial Public Class App
    Inherits Application

    public Sub New()
        InitializeComponent()
    End Sub

    Private Sub Application_Startup(ByVal o As Object, _
        ByVal e As StartupEventArgs) Handles Me.Startup

        ' Detect when the application starts up.

    End Sub

End Class

using System.Windows; // Application, StartupEventArgs

namespace SilverlightApplication
{
    public partial class App : Application
    {
        public App()
        {
            this.Startup += this.Application_Startup;
            InitializeComponent();
        }

        private void Application_Startup(object sender, StartupEventArgs e)
        {
            // Detect when the application starts up.
        }
    }
}