chartingToolkit:Chart how to show value of each pie

Question

I'm using System.Windows.Controls.DataVisualization.Charting to draw PieChart. But I don' know how to show the percentage/Value of each Pie Slice on the chart. Is that possible?

Answer 1

Adding percentage to a System.Windows.Controls.DataVisualization.Charting PieChart is not so immediate, since there are no properties for managing labels.

Anyway there are some ways to reach the goal. I wrote an article on my blog to describe the one I used.

The first step is to create a custom PieDataPoint class:

public class PieDataPoint : System.Windows.Controls.DataVisualization.Charting.PieDataPoint
{
    public static readonly DependencyProperty TextedGeometryProperty =
        DependencyProperty.Register("TextedGeometry", typeof(Geometry), typeof(PieDataPoint));

    public Geometry TextedGeometry
    {
        get { return (Geometry)GetValue(TextedGeometryProperty); }
        set { SetValue(TextedGeometryProperty, value); }
    }

    static PieDataPoint()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(PieDataPoint),
            new FrameworkPropertyMetadata(typeof(PieDataPoint)));
    }

    public PieDataPoint()
    {
        DependencyPropertyDescriptor dependencyPropertyDescriptor
            = DependencyPropertyDescriptor.FromProperty(GeometryProperty, GetType());

        dependencyPropertyDescriptor.AddValueChanged(this, OnGeometryValueChanged);
    }

    private double LabelFontSize
    {
        get
        {
            FrameworkElement parentFrameworkElement = Parent as FrameworkElement;
            return Math.Max(8, Math.Min(parentFrameworkElement.ActualWidth,
                parentFrameworkElement.ActualHeight) / 30);
        }
    }

    private void OnGeometryValueChanged(object sender, EventArgs arg)
    {
        Point point;
        FormattedText formattedText;

        CombinedGeometry combinedGeometry = new CombinedGeometry();
        combinedGeometry.GeometryCombineMode = GeometryCombineMode.Exclude;

        formattedText = new FormattedText(FormattedRatio, 
            CultureInfo.CurrentCulture,
            FlowDirection.LeftToRight,
            new Typeface("Arial"), 
            LabelFontSize, 
            Brushes.White);

        if (ActualRatio == 1)
        {
            EllipseGeometry ellipseGeometry = Geometry as EllipseGeometry;

            point = new Point(ellipseGeometry.Center.X - formattedText.Width / 2,
                ellipseGeometry.Center.Y - formattedText.Height / 2);
        }
        else if (ActualRatio == 0)
        {
            TextedGeometry = null;
            return;
        }
        else
        {
            Point tangent;
            Point half;
            Point origin;

            PathGeometry pathGeometry = Geometry as PathGeometry;
            pathGeometry.GetPointAtFractionLength(.5, out half, out tangent);
            pathGeometry.GetPointAtFractionLength(0, out origin, out tangent);

            point = new Point(origin.X + ((half.X - origin.X) / 2) - formattedText.Width / 2,
                origin.Y + ((half.Y - origin.Y) / 2) - formattedText.Height / 2);

        }

        combinedGeometry.Geometry1 = Geometry;
        combinedGeometry.Geometry2 =  formattedText.BuildGeometry(point);

        TextedGeometry = combinedGeometry;
    }
}

As you can see it adds a FormattedText geometry (with the percentage) to the original Geometry. Then you need to create a default style (in a generic.xaml dictionary) for using the new geometry property (named TextedGeometry).

The style has to contain - at least - something like that:

<Path Name="Slice" Data="{TemplateBinding local:PieDataPoint.TextedGeometry}" 
            Fill="{TemplateBinding Control.Background}" 
            Stroke="{TemplateBinding Control.BorderBrush}" 
            StrokeMiterLimit="1">
    <ToolTipService.ToolTip>
        <StackPanel>
            <ContentControl Content="{TemplateBinding chartingToolkit:DataPoint.FormattedDependentValue}" />
            <ContentControl Content="{TemplateBinding chartingToolkit:PieDataPoint.FormattedRatio}" />
        </StackPanel>
    </ToolTipService.ToolTip>
</Path>

As you can see the "Slice" path has its Data property binded to TextedGeometry.

Now with a custom PieSeries we can force the Chart control to use our PieDataPoint:

public class PieSeries : System.Windows.Controls.DataVisualization.Charting.PieSeries
{
    protected override DataPoint CreateDataPoint()
    {
        return new PieDataPoint();
    }
}

so in your XAML you can use:

<chartingToolkit:Chart Name="pieChart" Title="Pie Series Demo">
    <local:PieSeries DependentValuePath="Value" IndependentValuePath="Key"
                        ItemsSource="{Binding}" IsSelectionEnabled="True" />

</chartingToolkit:Chart>

Where local refers to your custom namespace. I hope it can help you.