using System;
using System.Drawing;
using System.Windows.Forms;
using DevExpress.XtraCharts;
// ...

private void chartControl1_MouseClick(object sender, MouseEventArgs e) {
    // Obtain the object being clicked.
    ChartHitInfo hi = chartControl1.CalcHitInfo(e.X, e.Y);

    // Check whether it was a series point, and if so - 
    // obtain its argument, and pass it to the detail series.
    SeriesPoint point = hi.SeriesPoint;

    if (point != null) {
        string argument = point.Argument.ToString();

        // Flip the series.
        if (chartControl1.Series[0].Visible == true) {
            chartControl1.Series[0].Visible = false;

            chartControl1.Series[1].Name = argument;
            chartControl1.Series[1].Visible = true;

            // Since the new series determines another diagram's type,
            // you should re-define the axes properties.
            XYDiagram diagram = (XYDiagram)chartControl1.Diagram;
            diagram.AxisX.Label.Angle = -25;
            diagram.AxisX.Label.Antialiasing = true;
            diagram.AxisY.NumericOptions.Format = NumericFormat.Currency;
            diagram.AxisY.NumericOptions.Precision = 0;

            chartControl1.Series[1].DataFilters[0].Value = argument;

            chartControl1.Titles[0].Visible = true;
            chartControl1.Titles[1].Text = "Personal Sales by Categories";
        }
    }

    // Obtain the title under the test point.
    ChartTitle link = hi.ChartTitle;

    // Check whether the link was clicked, and if so - 
    // restore the main series.
    if (link != null && link.Text.StartsWith("Back")) {
        chartControl1.Series[0].Visible = true;
        chartControl1.Series[1].Visible = false;

        link.Visible = false;
        chartControl1.Titles[1].Text = "Sales by Person";
    }
}

Imports System
Imports System.Drawing
Imports System.Windows.Forms
Imports DevExpress.XtraCharts
' ...

Private Sub chartControl1_MouseClick(ByVal sender As Object, _ 
ByVal e As MouseEventArgs) Handles chartControl1.MouseClick
    ' Obtain the object being clicked.
    Dim hi As ChartHitInfo = chartControl1.CalcHitInfo(e.X, e.Y)

    ' Check whether it was a series point, and if so - 
    ' obtain its argument, and pass it to the detail series.
    Dim point As SeriesPoint = hi.SeriesPoint

    If point IsNot Nothing Then
        Dim argument As String = point.Argument.ToString()

        ' Flip the series.
        If chartControl1.Series(0).Visible = True Then
            chartControl1.Series(0).Visible = False

            chartControl1.Series(1).Name = argument
            chartControl1.Series(1).Visible = True

            ' Since the new series determines another diagram's type,
            ' you should re-define axes properties.
            Dim diagram As XYDiagram = CType(chartControl1.Diagram, XYDiagram)
            diagram.AxisX.Label.Angle = -25
            diagram.AxisX.Label.Antialiasing = True
            diagram.AxisY.NumericOptions.Format = NumericFormat.Currency
            diagram.AxisY.NumericOptions.Precision = 0

            chartControl1.Series(1).DataFilters(0).Value = argument

            chartControl1.Titles(0).Visible = True
            chartControl1.Titles(1).Text = "Personal Sales by Categories"
        End If
    End If

    ' Obtain the title under the test point.
    Dim link As ChartTitle = hi.ChartTitle

    ' Check whether the link was clicked, and if so - 
    ' restore the main series.
    If link IsNot Nothing AndAlso link.Text.StartsWith("Back") Then
        chartControl1.Series(0).Visible = True
        chartControl1.Series(1).Visible = False

        link.Visible = False
        chartControl1.Titles(1).Text = "Sales by Person"
    End If
End Sub