Multiple pie chart labels

[Christopher]

Hi,

I'm trying to display multiple labels simultaneously next to each other on a pie chart. I found an old thread that made reference to this workaround. However, I'm having trouble implementing this strategy, because it seems the DataPoint is always {0, 0, 0, 0}. How can this be done? Thanks!

[Victor]

Hi Chris,

Thanks for writing.
Please explain in more detail about your scenario. By "the DataPoint is always {0,0,0,0}" do you mean that the point's LayoutSlot is {0,0,0,0}? The thread your linked to seems to contain a working example. Can you please send a sample application that demonstrates you scenario. This way I can debug/tweak it and help you further.
I am looking forward to your reply.

Greetings,
Victor
the Telerik team

[Christopher]

Hi Victor,

This appears to be a bug in RadPieChart, as I've used this same approach with success in a RadCartesianChart. The RadPieChart I'm using is defined as follows:

<telerik:RadPieChart>
    <telerikChart:PieSeries ValueBinding="Value">
        <telerikChart:PieSeries.LabelDefinitions>
            <telerikChart:ChartSeriesLabelDefinition>
                <telerikChart:ChartSeriesLabelDefinition.Strategy>
                    <core:PieChartLabelStrategy />
                </telerikChart:ChartSeriesLabelDefinition.Strategy>
            </telerikChart:ChartSeriesLabelDefinition>
        </telerikChart:PieSeries.LabelDefinitions>
    </telerikChart:PieSeries>
</telerikChart:RadPieChart>

And PieChartLabelStrategy can be anything as simple as:

public class PieChartLabelStrategy : ChartSeriesLabelStrategy
{
    public override LabelStrategyOptions Options
    {
        get
        {
            return LabelStrategyOptions.Arrange;
        }
    }

    public override RadRect GetLabelLayoutSlot(DataPoint point, FrameworkElement visual, int labelIndex)
    {
        return base.GetLabelLayoutSlot(point, visual, labelIndex);
    }
}

Putting a breakpoint on the call to the base method shows that point.LayoutSlot is always {0,0,0,0}.

Any help you can provide is appreciated! Thanks!

[Victor]

Hi Christopher,

Thank you for writing again.
Please have a look at this implementation of the layout strategy. You can use it as a basis for further tweaking.

public partial class MainPage : PhoneApplicationPage
    {
        public MainPage()
        {
            InitializeComponent();
            this.chart.Series[0].ItemsSource = new int[] { 1,1,1,1 };

            PieChartLabelStrategy strategy = new PieChartLabelStrategy(this.chart);
            ChartSeriesLabelDefinition definition = new ChartSeriesLabelDefinition();
            definition.Strategy = strategy;

            this.chart.Series[0].LabelDefinitions.Add(definition);
        }
    }

    public class PieChartLabelStrategy : ChartSeriesLabelStrategy
    {
        RadPieChart chart;
        public PieChartLabelStrategy(RadPieChart chart)
        {
            this.chart = chart;
        }

        public override LabelStrategyOptions Options
        {
            get
            {
                return LabelStrategyOptions.Arrange;
            }
        }

        public override RadRect GetLabelLayoutSlot(DataPoint point, FrameworkElement visual, int labelIndex)
        {
            PieDataPoint piePoint = (PieDataPoint)point;

            IChartView view = this.chart as IChartView;
            Point center = new Point(view.ViewportWidth / 2, view.ViewportHeight / 2);
            double radius = (Math.Min(view.ViewportWidth , view.ViewportHeight) / 2) * 0.5;
            visual.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
            Size pointSize = new Size(visual.ActualWidth, visual.ActualHeight);

            RadRect result = RadRect.Empty;
            double angle = Math.Round(piePoint.StartAngle + piePoint.SweepAngle / 2) * 0.0174532925;
            result.X = (center.X + radius * Math.Cos(angle)) - pointSize.Width / 2;
            result.Y = (center.Y + radius * Math.Sin(angle)) - pointSize.Height / 2;
            result.Width = pointSize.Width;
            result.Height = pointSize.Height;

            return result;
        }
    }

<telerikChart:RadPieChart x:Name="chart"
                          Palette="Warm">
    <telerikChart:PieSeries ValueBinding="Value"/>
</telerikChart:RadPieChart>

Please write again if you need further assistance.

Regards,
Victor
the Telerik team