private void AddFile()
        {
            string filePath = testMode ?
                              Path.GetFullPath(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, @"../../../File Examples/file_example_1.mp3")) :
                              GetFilePath_OpenDialog("mp3");

            if (filePath != null && File.Exists(filePath) && !BasicFunctions.FileInUse(filePath))
            {
                // check if File is already in list
                bool FileIsInList = false;
                foreach (MusicFileTag FileInList in MusicFileTags)
                {
                    if (FileInList.FilePath == filePath)
                    {
                        FileIsInList = true;
                        MessageBox.Show("This file is already in the list");
                    }
                }
                if (!FileIsInList)
                {
                    MusicFileTag newFile = TaggingLogic.AddFile(filePath);
                    MusicFileTags.Add(newFile);
                    NumberOfFiles++;
                }
            }
            else
            {
                if (BasicFunctions.FileInUse(filePath))
                {
                    MessageBox.Show("Sorry, this file cannot be opened. " +
                                    "Either it is currently in use or this program does not have the necessary rights to read the file.");
                }
            }
        }
 private void RemoveFile()
 {
     MusicFileTags.Remove(SelectedFile);
     NumberOfFiles--;
 }