C＃Windows窗体将更多文件添加到播放列表

Question

将更多文件添加到我的播放列表时，它会引发超出范围的异常。第一次加载文件时，它不会引发异常。我认为问题是因为playlist.SelectedIndex需要在其中放置一个值。有什么想法吗？

private void mediaPlayer_PlayStateChange(object sender, AxWMPLib._WMPOCXEvents_PlayStateChangeEvent e)
{
    if (e.newState == 1)
    {
        if (playlist.SelectedIndex < playlist.Items.Count)
        {
            BeginInvoke(new Action(() => {    
                if ((playlist.SelectedIndex + 1) < playlist.Items.Count)
                {
                     mediaPlayer.URL = paths[playlist.SelectedIndex];
                     playlist.SelectedIndex++;
                }
                else 
                {
                    mediaPlayer.Ctlcontrols.stop();
                }
            }));
        }
    }
}

private void load_button_Click(object sender, EventArgs e)
{
    OpenFileDialog ofd = new OpenFileDialog();
    ofd.Multiselect = true;
    if (ofd.ShowDialog() == DialogResult.OK)
    {
        files = ofd.SafeFileNames;
        paths = ofd.FileNames;
    }

    for (int i =0; i< files.Length; i++)
    {
        playlist.Items.Add(files[i]);
    }

    playlist.SelectedIndex = 0;

}