private void Concat_Click(object sender, RoutedEventArgs e) { Music first = firstMp3.SelectedItem as Music; Music second = secondMp3.SelectedItem as Music; if (first != null && second != null) { string[] mp3Paths = new string[] { first.FilePath, second.FilePath }; string pathWithoutExtension = first.FilePath.Split('.')[0]; string outputName = pathWithoutExtension + "+" + second.Name; musicService.Combine(mp3Paths, outputName, first.DirectoryId); } }