How to offset PieSeries slice by clicking on a LegendItemElement

Updated over 6 months ago

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.

C#

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;
		}
	}
}

VB.NET

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