WPF: Binding lists in XAML- how can an item know its position in the list?

Question

Given the following XAML code that with a ListControl like behavior:

Answer 1

This sample supports sorting:

Numbered listbox

Answer 2

According to MSDN Magazine article "Charting with DataTemplates":

[...]the DataTemplate would need access to the index of the particular data item in the collection. But it's easy enough to include this information in the business object[...]

So, unless there was a change in .NET 4, there is no "index of this item" property unless it is explicitly included in the model.

Answer 3

Here is a hack solution. We can use Value Conversion with DataBinding. So the first step is to declare our ValueConvertor:

public class ListItemToPositionConverter : IValueConverter
    {
        #region Implementation of IValueConverter

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var item = value as ListBoxItem;
            if (item != null)
            {
                var lb = FindAncestor<ListBox>(item);
                if (lb != null)
                {
                    var index = lb.Items.IndexOf(item.Content);
                    return index;
                }
            }
            return null;
        }            

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }

        #endregion
    }

Declare wherever you want this static method in order to obtain ListBox parent:

public static T FindAncestor<T>(DependencyObject from) where T : class
        {
            if (from == null)
                return null;

            var candidate = from as T;
            return candidate ?? FindAncestor<T>(VisualTreeHelper.GetParent(from));
        }

Then in ListBox.Resources declare our convertor as follows:

<ListBox.Resources>
                <YourNamespace:ListItemToPositionConverter x:Key="listItemToPositionConverter"/>
            </ListBox.Resources>

And finally - DataTemplate:

<ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ListBoxItem}}, Converter={StaticResource listItemToPositionConverter}}"/>
                        <Label Content="{Binding Path=DisplayName}"></Label>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>

Note: in this example the items will be numerated starting with 0 (zero), you can change it in Convert method by adding 1 to result.

Hope this helps...