public void SaveSongsList()
        {
            string fileName = SaveNewXMLFile();

            DataCollectionLoader.SaveCollection(Songs.Select(s => new Song
            {
                Url    = s.Url,
                Title  = s.Title,
                Author = s.Author,
                IsGonnaBeDownloaded = s.IsGonnaBeDownloaded
            }).ToArray(), fileName);
        }
        public void AddSongsList()
        {
            string nameOfSelectedFile;

            if (!LoadXMLFile(out nameOfSelectedFile))
            {
                MessageBox.Show(Application.Current.MainWindow, "Błąd wczytywania pliku", "BŁĄD", MessageBoxButton.OK,
                                MessageBoxImage.Information);
            }
            else
            {
                Songs.AddRange(DataCollectionLoader.LoadCollection <Song>(nameOfSelectedFile));
                NotifyOfPropertyChange(nameof(Songs));
            }
        }