SL Toolkit chart - clickable legend items

The Silverlight Toolkit chart allows for click-though by setting IsSelectionEnabled to true on the series, and attaching the SelectionChanged event. Now you can click on bars or pie slices, and interact on that.

But what if you want to also make the legend beside the chart clickable. That's not supported out of the box. You do this by changing the Legend Items template.

The template

Define a template like the following for the legend items. I've put this as a resource in the Grid that contains my Chart.

<Grid.Resources>
 <Style x:Key="CategoryLegendItem" TargetType="toolkit:LegendItem">
  <Setter Property="Template">
   <Setter.Value>
    <ControlTemplate TargetType="toolkit:LegendItem">
     <StackPanel Orientation="Horizontal">
      <Rectangle Width="8" Height="8" Fill="{Binding Background}" Stroke="{Binding BorderBrush}" StrokeThickness="1" Margin="0,0,3,0" />
      <HyperlinkButton Content="{TemplateBinding Content}" Click="HyperlinkButton_Click" />
     </StackPanel>
    </ControlTemplate>
   </Setter.Value>
  </Setter>
 </Style>
</Grid.Resources>

Notice how I replaced the default Title element that displays the legend item text by a HyperlinkButton. That way it actually looks like something that can be clicked. This button also triggers the click event.

The code

First, the series LegendItemStyle must be set to the custom template. Since my chart is created in code I've put:

series.LegendItemStyle = (Style)LayoutRoot.Resources["CategoryLegendItem"]

Finally there's the HyperlinkButtons click handler.

private void HyperlinkButton_Click(object sender, RoutedEventArgs e) {
  RowPrestation row = (RowPrestation)((sender as HyperlinkButton)
                      .DataContext as PieDataPoint).DataContext;
  PieSeries series = (PieSeries)(Chart.Child as Chart).Series[0];
  series.SelectedItem = row;
}

Notice that the DataContext of the HyperlinkButton contains the PieDataPoint — in case of a pie chart — that goes with the legend item in question. And if you cast it, that points DataContext contains the bound object that was used as ItemsSource. Mine was a List<RowPrestation>.