http://ko.infragistics.com/community/forums/p/73058/369756.aspx#369756

which is already discussed.

Here's one way to do it:

The xaml:

<UserControl.Resources>
        <DataTemplate x:Key="ToolTipTemplate">
            <Border CornerRadius="5" 
                    Background="AliceBlue">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding Label}" />
                    <TextBlock Text=":"/>
                    <TextBlock Text="{Binding Value}" />
                </StackPanel>
            </Border>

        </DataTemplate>
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot">
        <igChart:XamWebChart>
            <igChart:XamWebChart.Series>
                <igChart:Series ChartType="Column" DataSource="{Binding}"
                                DataMapping="Label = Label; Value = Value; ToolTip = ToolTip"/>
            </igChart:XamWebChart.Series>
        </igChart:XamWebChart>
    </Grid>

And the code behind:

public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();

            DataContext = GetSampleData();
        }

        private ObservableCollection GetSampleData()
        {
            DataTemplate template = 
                (DataTemplate)this.Resources["ToolTipTemplate"];
            ObservableCollection data =
                new ObservableCollection()
                {
                    new TestDataItem(template)
                    {
                        Label = "Item A",
                        Value = 1
                    },
                    new TestDataItem(template)
                    {
                        Label = "Item B",
                        Value = 2
                    },
                    new TestDataItem(template)
                    {
                        Label = "Item C",
                        Value = 3
                    }
                };

            return data;
        }
    }

    public class TestDataItem
        : INotifyPropertyChanged
    {
        public TestDataItem(DataTemplate template)
        {
            toolControl = new ContentControl();
            toolControl.ContentTemplate = template;
            toolControl.Content = this;
        }

        private string label; 
        public string Label 
        {
            get
            {
                return label;
            }
            set
            {
                label = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(
                        this,
                        new PropertyChangedEventArgs("Label"));
                }
            }
        }
        private double value;
        public double Value
        {
            get
            {
                return this.value;
            }
            set
            {
                this.value = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(
                        this,
                        new PropertyChangedEventArgs("Value"));
                }
            }
        }
        
        private ContentControl toolControl;   
        public object ToolTip 
        {
            get
            {
                return toolControl;
            }
        }

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }

Notice the ToolTip for each item is object type, so you can bind whatever you want in. You could just have each item have a property that creates a control on the fly based on its values. Here I elected to use a content control and have the data template be defined in the xaml, for ease of editing. Does this help?

-Graham