[WPF] 別スレッドでUIスレッドを立ててそこからWindowを表示

ShowWindowOnNewUIThread.cs

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace 別スレッドでポップアップ表示
{
    /// <summary>
    /// 参照リソース
    /// http://reedcopsey.com/2011/11/28/launching-a-wpf-window-in-a-separate-thread-part-1/
    /// https://eprystupa.wordpress.com/2008/07/28/running-wpf-application-with-multiple-ui-threads/
    /// http://stackoverflow.com/questions/1111369/how-do-i-create-and-show-wpf-windows-on-separate-threads
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Btn1_Click(object sender, RoutedEventArgs e)
        {
            var t = new Thread(() =>
            {
                SynchronizationContext.SetSynchronizationContext(
                    new DispatcherSynchronizationContext(Dispatcher.CurrentDispatcher)
                );
                
                var newWindow = new Popup1();

                newWindow.Closed += (o, args) =>
                {
                    Dispatcher.CurrentDispatcher.BeginInvokeShutdown(DispatcherPriority.Background);
                };

                newWindow.Topmost = true;
                newWindow.Show();
                Dispatcher.Run();
            });

            t.SetApartmentState(ApartmentState.STA);
            t.IsBackground = true;

            t.Start();
        }
    }
}