private void showMessagesButton_Click(object sender, RoutedEventArgs e)
 {
     if (selectedThread == null)
     {
         MessageBox.Show("Nie wybrano wątku!", "Błąd", MessageBoxButton.OK);
     }
     else
     {
         var window = new MessagesWindow(selectedThread, user);
         window.Show();
         Close();
     }
 }
 private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
 {
     var window = new MessagesWindow(thread, user);
     window.Show();
 }