How to offset PieSeries slice by clicking on a LegendItemElement

Environment

Product Version	Product	Author
2022.2.510	RadChartView for WinForms	Dinko Krastev

Description

In the following topic, we will demonstrate how we can offset PieSeries slices by clicking on its corresponding legend item.

Solution

This behavior can be achieved by handling the MouseDown event of the chart. In the event handler, we will need to find the associated data point with the clicked LegendItemElement.

public Form1()
{
    InitializeComponent();

    this.radChartView1.AreaType = ChartAreaType.Pie;
    PieSeries series = new PieSeries();
    series.DataPoints.Add(new PieDataPoint(50, "Germany"));
    series.DataPoints.Add(new PieDataPoint(70, "United States"));
    series.DataPoints.Add(new PieDataPoint(40, "France"));
    series.DataPoints.Add(new PieDataPoint(25, "United Kingdom"));
    series.ShowLabels = true;

    this.radChartView1.Series.Add(series);
    this.radChartView1.ShowLegend = true;
    this.radChartView1.MouseDown += radChartView1_MouseDown;
}

private void radChartView1_MouseDown(object sender, MouseEventArgs e)
{
    RadChartView chart = (RadChartView)sender;
    RadElement element = chart.ElementTree.GetElementAtPoint(e.Location);
    LegendItemElement itemElement = chart.ElementTree.GetElementAtPoint(e.Location) as LegendItemElement;
    if (itemElement == null)
    {
        RadElement parent = element.Parent;
        while (parent != null)
        {
            if (parent is LegendItemElement)
            {
                itemElement = (LegendItemElement)parent;
                break;
            }

            parent = parent.Parent;
        }
    }

    if (itemElement != null)
    {
        PieDataPoint dataPoint = ((PiePointElement)itemElement.LegendItem.Element).DataPoint as PieDataPoint;
        if (dataPoint.OffsetFromCenter > 0)
        {
            dataPoint.OffsetFromCenter = 0;
        }
        else
        { 
            dataPoint.OffsetFromCenter = 0.1;
        }
    }
}

Public Sub New()
    InitializeComponent()
    Me.radChartView1.AreaType = ChartAreaType.Pie
    Dim series As PieSeries = New PieSeries()
    series.DataPoints.Add(New PieDataPoint(50, "Germany"))
    series.DataPoints.Add(New PieDataPoint(70, "United States"))
    series.DataPoints.Add(New PieDataPoint(40, "France"))
    series.DataPoints.Add(New PieDataPoint(25, "United Kingdom"))
    series.ShowLabels = True
    Me.radChartView1.Series.Add(series)
    Me.radChartView1.ShowLegend = True
    AddHandler Me.radChartView1.MouseDown, AddressOf radChartView1_MouseDown
End Sub

Private Sub radChartView1_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs)
    Dim chart As RadChartView = CType(sender, RadChartView)
    Dim element As RadElement = chart.ElementTree.GetElementAtPoint(e.Location)
    Dim itemElement As LegendItemElement = TryCast(chart.ElementTree.GetElementAtPoint(e.Location), LegendItemElement)

    If itemElement Is Nothing Then
        Dim parent As RadElement = element.Parent

        While parent IsNot Nothing

            If TypeOf parent Is LegendItemElement Then
                itemElement = CType(parent, LegendItemElement)
                Exit While
            End If

            parent = parent.Parent
        End While
    End If

    If itemElement IsNot Nothing Then
        Dim dataPoint As PieDataPoint = TryCast((CType(itemElement.LegendItem.Element, PiePointElement)).DataPoint, PieDataPoint)

        If dataPoint.OffsetFromCenter > 0 Then
            dataPoint.OffsetFromCenter = 0
        Else
            dataPoint.OffsetFromCenter = 0.1
        End If
    End If
End Sub