App.xaml.cs

using System.Threading;
using System.Windows;

namespace BF1RecordQuery
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        public static ISplashScreen splashScreen;

        private ManualResetEvent ResetSplashCreated;
        private Thread SplashThread;

        protected override void OnStartup(StartupEventArgs e)
        {
            ResetSplashCreated = new ManualResetEvent(false);

            SplashThread = new Thread(ShowSplash);
            SplashThread.SetApartmentState(ApartmentState.STA);
            SplashThread.IsBackground = true;
            SplashThread.Name = "Splash Screen";
            SplashThread.Start();

            ResetSplashCreated.WaitOne();

            base.OnStartup(e);
        }

        private void ShowSplash()
        {
            LaunchWindow launchWindow = new LaunchWindow();
            splashScreen = launchWindow;

            launchWindow.Show();

            ResetSplashCreated.Set();
            System.Windows.Threading.Dispatcher.Run();
        }
    }
}