RKIS/Task1/ViewModel/Helper.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;

namespace Task1.ViewModel
{
    class Helper
    {
        private static TaskContext context;
        public static void CloseWindowsAtType<T>()
        {
            foreach(var t in App.Current.Windows)
            {
                if(t is T)
                {
                    ((Window)t).Close();
                }
            }
        }
    }
}