Numbered listbox

Question

I have a sorted listbox and need to display each item's row number. In this demo I have a Person class with a Name string property. The listbox displays a a list of Persons sorted by Name. How can I add to the datatemplate of the listbox the row number???

XAML:

<Window x:Class="NumberedListBox.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="300" Width="300">
    <ListBox 
        ItemsSource="{Binding Path=PersonsListCollectionView}" 
        HorizontalContentAlignment="Stretch">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Path=Name}" />
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
</Window>

Code behind:

using System;
using System.Collections.ObjectModel;
using System.Windows.Data;
using System.Windows;
using System.ComponentModel;

namespace NumberedListBox
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Persons = new ObservableCollection<Person>();
            Persons.Add(new Person() { Name = "Sally"});
            Persons.Add(new Person() { Name = "Bob" });
            Persons.Add(new Person() { Name = "Joe" });
            Persons.Add(new Person() { Name = "Mary" });

            PersonsListCollectionView = new ListCollectionView(Persons);
            PersonsListCollectionView.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));

            DataContext = this;
        }

        public ObservableCollection<Person> Persons { get; private set; }
        public ListCollectionView PersonsListCollectionView { get; private set; }
    }

    public class Person
    {
        public string Name { get; set; }
    }
}

Answer 1

This should get you started:

http://weblogs.asp.net/hpreishuber/archive/2008/11/18/rownumber-in-silverlight-datagrid-or-listbox.aspx

It says it's for Silverlight, but I don't see why it wouldn't work for WPF. Basically, you bind a TextBlock to your data and use a custom value converter to output the current item's number.

Answer 2

The idea in David Brown's link was to use a value converter which worked. Below is a full working sample. The list box has row numbers and can be sorted on both name and age.

XAML:

    <Window x:Class="NumberedListBox.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:NumberedListBox"
    Height="300" Width="300">

    <Window.Resources>

        <local:RowNumberConverter x:Key="RowNumberConverter" />

        <CollectionViewSource x:Key="sortedPersonList" Source="{Binding Path=Persons}" />

    </Window.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ListBox 
            Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2"
            ItemsSource="{Binding Source={StaticResource sortedPersonList}}" 
            HorizontalContentAlignment="Stretch">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock 
                            Text="{Binding Converter={StaticResource RowNumberConverter}, ConverterParameter={StaticResource sortedPersonList}}" 
                            Margin="5" />
                        <TextBlock Text="{Binding Path=Name}" Margin="5" />
                        <TextBlock Text="{Binding Path=Age}" Margin="5" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <Button Grid.Row="1" Grid.Column="0" Content="Name" Tag="Name" Click="SortButton_Click" />
        <Button Grid.Row="1" Grid.Column="1" Content="Age" Tag="Age" Click="SortButton_Click" />
    </Grid>
</Window>

Code behind:

using System;
using System.Collections.ObjectModel;
using System.Windows.Data;
using System.Windows;
using System.ComponentModel;
using System.Windows.Controls;

namespace NumberedListBox
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Persons = new ObservableCollection<Person>();
            Persons.Add(new Person() { Name = "Sally", Age = 34 });
            Persons.Add(new Person() { Name = "Bob", Age = 18 });
            Persons.Add(new Person() { Name = "Joe", Age = 72 });
            Persons.Add(new Person() { Name = "Mary", Age = 12 });

            CollectionViewSource view = FindResource("sortedPersonList") as CollectionViewSource;
            view.SortDescriptions.Add(new SortDescription("Name", ListSortDirection.Ascending));

            DataContext = this;
        }

        public ObservableCollection<Person> Persons { get; private set; }

        private void SortButton_Click(object sender, RoutedEventArgs e)
        {
            Button button = sender as Button;
            string sortProperty = button.Tag as string;
            CollectionViewSource view = FindResource("sortedPersonList") as CollectionViewSource;
            view.SortDescriptions.Clear();
            view.SortDescriptions.Add(new SortDescription(sortProperty, ListSortDirection.Ascending));

            view.View.Refresh();
        }
    }

    public class Person
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }
}

Value converter:

using System;
using System.Windows.Data;

namespace NumberedListBox
{
    public class RowNumberConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            CollectionViewSource collectionViewSource = parameter as CollectionViewSource;

            int counter = 1;
            foreach (object item in collectionViewSource.View)
            {
                if (item == value)
                {
                    return counter.ToString();
                }
                counter++;
            }
            return string.Empty;
        }

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

Answer 3

Finally! If found a way much more elegant and probably with better performance either. (see also http://stackoverflow.com/questions/2007177/accessing-an-itemscontrol-item-as-it-is-added/2007747#2007747)

We "misuse" property ItemsControl.AlternateIndex for this. Originally it is intended to handle every other row within a ListBox differently. (see http://msdn.microsoft.com/en-us/library/system.windows.controls.itemscontrol.alternationcount.aspx)

1. Set AlternatingCount to the amount of items contained in the ListBox

<ListBox ItemsSource="{Binding Path=MyListItems}"
         AlternationCount="{Binding Path=MyListItems.Count}"
         ItemTemplate="{StaticResource MyItemTemplate}"
...
/>

2. Bind to AlternatingIndex your DataTemplate

<DataTemplate x:Key="MyItemTemplate" ... >
    <StackPanel>
        <Label Content="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplatedParent.(ItemsControl.AlternationIndex)}" />
        ...
    </StackPanel>
</DataTemplate>

So this works without, converter, extra CollectionViewSource and most important without brute-force-searching the source collection.