Question

If I create a class that extends WPF’s ListBoxItem, create a list of these objects, try to bind the list to a ListBox’s ItemsSource, the items will not display:

<ListBox ItemsSource="{Binding Path=LbData, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}">
    <ListBox.ItemTemplate>
        <DataTemplate >
            <TextBlock Text="{Binding Path=Display}" Margin="1" />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

public partial class MainWindow : Window
{
    public IEnumerable lbData = new List<LbItem>();
    public IEnumerable LbData
    {
        get { return lbData; }
        set { lbData = value; }
    }

    public MainWindow()
    {
        InitializeComponent();
        LbData = new List<LbItem> { new LbItem("a"), new LbItem("b") };
    }
}

public class LbItem : ListBoxItem
{
    public string Display { get; private set; }

    public LbItem(string v)
    {
        Display = v;
    }
}

I’m new to WPF and don’t see why this should be an issue. TIA

Answer 1

The ItemsSource normally is used for data-objects, and what you do there (setting the ItemTemplate) suggest that you should not make your object inherit from ListBoxItem at all, instead it should be a normal object (possibly implementing INotifyPropertyChanged if properties may change after creation). If the list changes it should implement INotifyCollectionChanged.

Because the items are already ListBoxItems the DataTemplate you set will be disregarded. There should be the following error in your Visual Studio Output-window:

System.Windows.Data Error: 26 : ItemTemplate and ItemTemplateSelector are ignored for items already of the ItemsControl’s container type; Type=’LbItem’