SingleInstance.cs

namespace Rido.SingleInstance
{
    public class SingleInstanceManager<T> : Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase 
        where T: System.Windows.Application, new()
    {
        T app;
        public SingleInstanceManager()
        {
            base.IsSingleInstance = true;
        }

        protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
        {
            app = new T();
            app.Run();
            return false;
        }

        protected override void OnStartupNextInstance(Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs e)
        {
            app.MainWindow.Activate();            
        }
    }
}