如何让媒体元素自动播放下一个列表框项目？

Question

I'm making a media player where I add media files to a list-box. What I would like to do is to make the media-element automatically start playing the next song/video in the list-box after the current one has ended. Also I would like to make a doubleclickevent where if listitem clicked the song/video should play. This is what I currently have:

Xaml:

<MediaElement Name="objMediaPlayer" LoadedBehavior="Manual" UnloadedBehavior="Stop" MediaOpened="objMediaPlayer_MediaOpened" MediaEnded="objMediaPlayer_MediaEnded" Margin="20,19,20,40" ButtonBase.Click="mediaItemList_MouseDoubleClick" />

<ListBox Canvas.Left="882" Canvas.Top="12" Height="467" Name="mediaItemList" Width="260" Background="Gray" MouseDoubleClick="mediaItemList_MouseDoubleClick" />

cs-sheet:

 private void BrowseButtonClick(object sender, RoutedEventArgs e)
    {
        System.Windows.Forms.OpenFileDialog dlg = new System.Windows.Forms.OpenFileDialog();
        dlg.Multiselect = true;
        dlg.InitialDirectory = "c:\\";
        dlg.Filter = "All Files (*.*)|*.*";
        dlg.RestoreDirectory = true;

        if (dlg.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            foreach (string file in dlg.FileNames)
            {
                FileInfo fileName = new FileInfo(file);
                mediaItemList.Items.Add(fileName);
            }
            string selectedFileName = dlg.FileName;
            fileNameLabel.Content = selectedFileName;
            objMediaPlayer.Source = new Uri(selectedFileName);
            objMediaPlayer.Play();
            lblCoverUp.Visibility = Visibility.Hidden;


        }
    }
private int currentSongIndex = -1;
    private void objMediaPlayer_MediaEnded(object sender, RoutedEventArgs e)
    {

            if (currentSongIndex == -1)
            {
                currentSongIndex = mediaItemList.SelectedIndex;
            }
            currentSongIndex++;
            if (currentSongIndex < mediaItemList.Items.Count)
            {

                objMediaPlayer.Play();
            }
            else
            {
                // last song in listbox has been played
            }           
    }



    private void mediaItemList_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

    }

For the Doubleclick function

    private void mediaItemList_MouseDoubleClick(object sender, RoutedEventArgs e)
    {
        System.Windows.Controls.Button prevButton = objMediaPlayer.Tag as System.Windows.Controls.Button;
        System.Windows.Controls.Button button = (sender as System.Windows.Controls.Button);
        FileInfo fileInfo = button.DataContext as FileInfo;

        // If a file is playing, stop it

        if (prevButton != null)
        {
            objMediaPlayer.Tag = null;
            objMediaPlayer.Stop();
            prevButton.Background = Brushes.LightYellow;
           // if the one thats playing is the one that was clicked -> don't play it
            if (prevButton == button)
                return;
        }
        // Play the one that was clicked
        objMediaPlayer.Tag = button;
        objMediaPlayer.Source = new Uri(fileInfo.FullName);
        objMediaPlayer.Play();
    }

For Media_ended I have already tried: objMediaPlayer.Play(mediaItemList.Items[currentSongIndex]);

When activating the Doubleclick event I get the following error:Object reference not set to an instance of an object. (FileInfo fileInfo = button.DataContext as FileInfo).

I hope someone can help me. If you need more information, just ask

EDIT: I have fixed mostly of the media ended problem by using the following code:

    private void objMediaPlayer_MediaEnded(object sender, RoutedEventArgs e)
    {
        objMediaPlayer.Stop();

        if (mediaItemList.SelectedIndex <= mediaItemList.Items.Count)
        {
            mediaItemList.SelectedIndex = mediaItemList.SelectedIndex += 1;
            fileNameLabel.Content = mediaItemList.SelectedItem;
            objMediaPlayer.Play();
        }
        else
        {
            objMediaPlayer.Stop();
            fileNameLabel.Content = " ";
        }
    }

The only problem now is that the player doesn't stop after finishing the last song(listitem). How do you fix this.

Answer 1

Surely you need to open each file before you play them?:

private void objMediaPlayer_MediaEnded(object sender, RoutedEventArgs e)
{
    if (currentSongIndex == -1)
    {
        currentSongIndex = mediaItemList.SelectedIndex;
    }
    currentSongIndex++;
    if (currentSongIndex < mediaItemList.Items.Count)
    {
        objMediaPlayer.Open(new Uri(mediaItemList.ElementAt(currentSongIndex), 
            UriKind.Absolute));            
    }
    else
    {
        // last song in listbox has been played
    }           
}

private void MediaPlayer_MediaOpened(object sender, EventArgs e)
{
    objMediaPlayer.Play();
}