ListBox does not get updated WPF

Question

The wrapper class:

public class Multimedia : INotifyPropertyChanged
{
   //... constructor
   //... empty constructor
   //... getters and setters for properties
   public event PropertyChangedEventHandler PropertyChanged;

   public void OnPropertyChanged(string name)
   {
       PropertyChangedEventHandler handler = PropertyChanged;
       if (handler != null)
       {
           handler(this, new PropertyChangedEventArgs(name));
       }
   }
}

The collection:

public class MultiMediaList : ObservableCollection<Multimedia>
{
        Multimedia mediaWrapper = new Multimedia();

        //... constructor with creating several default objects of Multimedia

        public void addMedia(string title, string artist, string genre, MediaType type)
        {
            this.Add(new Multimedia(title, artist, genre, type));
            mediaWrapper.OnPropertyChanged("MultiMediaList");
        }
}

This is how I bind the ListBox to the ObservableCollection: Code-behind:

public partial class MainWindow : Window
{
        MultiMediaList mediaList;
        public MainWindow()
        {
            InitializeComponent();
            mediaList = new MultiMediaList();
            LB_media.ItemsSource = mediaList;
        }
}

XAML:

<ListBox Name="LB_media" DisplayMemberPath="Title" ... />

Nevertheless, when I add a new entry in the Collection, the ListBox does not get updated. I tried debugging, to see whether at least the new entry is being added to the Collection - it is.

It all looks correct to me, from research that I did and tryouts. Any ideas where am I missing something or doing something wrong?

Answer 1

If all you're trying to do is add to the list, you don't need any wrapper classes or any events because ObservableCollection already implements INotifyCollectionChanged.

public class MultiMediaList : ObservableCollection<Multimedia>
{
    //... constructor with creating several default objects of Multimedia

    public void addMedia(string title, string artist, string genre, MediaType type)
    {
        this.Add(new Multimedia(title, artist, genre, type));
    }
}

That's it. Keep your MainWindow as-is. If you add a button to the form,

private void Button_Click(object sender, RoutedEventArgs e)
{
    mediaList.addMedia("ccc", "ccc", "ccc", MediaType.Whatever);
}

will cause the new item will automatically show up.