3rdpartylibs/fastreports.wpf/Demos/WPF/Main/App.xaml.cs

using System.Windows;

namespace WpfDemo
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        public App()
        {
            new DemoWindow().ShowDialog();
            
            // diagnostic - remove after testing
            if (Windows.Count > 0)
            {
                var str = "";
                foreach (Window win in Windows)
                {
                    str += win.Title;
                    if (win.Tag is object obj)
                        str += $" ({obj.GetType().Name})";
                    str += "\n";
                }
                MessageBox.Show($"The following {Windows.Count} window(s) still running:\n{str}\nPress OK to copy message to clipboard.", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
                Clipboard.SetText(str);
            }
        }
    }
}