Question: I'm plotting a histogram of a grayscale image using an array of 256 values. Im doing so by creating my own chart with 256 vertical rectangles (columns). My aim is that when I mouse over one rectangle I get its index value, its index from the array it lies in, like if I mouse over the 200th rectangle I get 200 in a small text box near cursor, like how ToolTip should perform. The problem is that I don't find the proper binding for ToolTip to get this working. I think the solution lies in the proper use of **AlternationCount** / **AlternationIndex**

Here is may XAML code, maybe someone can give me a fix for it:

```
<ItemsControl Grid.Row="1" ItemsSource="{Binding HistogramValues}" AlternationCount="{Binding Path=HistogramValues.Count}">              
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal" />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Rectangle Height="{Binding }" ToolTip="{Binding AlternationIndex, RelativeSource={RelativeSource AncestorType=ItemsControl}}" Width="2" VerticalAlignment="Bottom" Fill="Black"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate> 
</ItemsControl>

```

where in view model I have:

```
public float[] HistogramValues { get; set; }

```

I've found this useful post 
[Numbered listbox](https://stackoverflow.com/questions/745568/numbered-listbox/748383)
but I still cant make it run for my case, I'm confused about that **ItemTemplate** and **TemplatedParent** which I dont know if I need or if I need the template how should I code this.

Answer: 
If you are not ok with converters you can use this,

```
 <ItemsControl Grid.Row="1" ItemsSource="{Binding Collection}" AlternationCount="{Binding Path=Collection.Count}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <StackPanel Orientation="Vertical" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <TextBlock  Text="{Binding}" ToolTip="{Binding Path=(ItemsControl.AlternationIndex),   RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ContentPresenter}}">
                    </TextBlock>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>

```

Since AlternationIndex is attached property, it should be covered with "()".
If showing the index is your only requirement you can achieve this like below,,
MyConverter is a multiconverter ,and include that in resources

```
     <ItemsControl Grid.Row="1" ItemsSource="{Binding Collection}" >
                <ItemsControl.ItemContainerStyle>
                    <Style>
                        <Setter Property="Control.ToolTip">
                            <Setter.Value>
                                <MultiBinding Converter="{StaticResource MyConverter}">
                                    <Binding Path="IsMouseOver" RelativeSource="{RelativeSource Self}"/>
                                    <Binding />
                                    <Binding Path="ItemsSource" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}"/>
                                </MultiBinding>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </ItemsControl.ItemContainerStyle>
                <ItemsControl.ItemsPanel>
                    <ItemsPanelTemplate>
                        <StackPanel Orientation="Vertical" />
                    </ItemsPanelTemplate>
                </ItemsControl.ItemsPanel>
            </ItemsControl>

  public partial class MainWindow : Window
    {
        private ObservableCollection<string> collection;

        public ObservableCollection<string> Collection
        {
            get { return collection; }
            set { collection = value; }
        }

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
            collection = new ObservableCollection<string>();
            collection.Add("First");
            collection.Add("Second");
            collection.Add("Third");
            collection.Add("Fourth");

        }
    }

     public class MyConverter : IMultiValueConverter
        {
            public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                if ((bool)values[0])
                {
                    return (values[2] as ObservableCollection<string>).IndexOf(values[1].ToString());
                }
                else
                    return "";
            }

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

```