public event CustomExportWebEventHandler CustomExport

Public Event CustomExport As CustomExportWebEventHandler

using DevExpress.DashboardCommon;
using DevExpress.DashboardWeb;
using DevExpress.XtraCharts;
using DevExpress.XtraReports.UI;
using System;
using System.Drawing;
using System.Linq;

protected void CustomizeExport(object sender, CustomExportWebEventArgs e) {
  foreach(var printControl in e.GetPrintableControls()) {
    if(printControl.Value is XRGaugeDashboardItem) {
      var gaugeItemName = printControl.Key;
      var gaugeDashboardItem = e.GetDashboardItem(gaugeItemName) as GaugeDashboardItem;
      foreach(var dashGaugeElement in gaugeDashboardItem.Gauges) {
        foreach(var gaugePanel in e.GetGaugeContext(gaugeItemName).GetPrintableGauges(dashGaugeElement).Cast<XRDashboardGauge>()) {
          if(gaugePanel != null) {
              gaugePanel.MainSeriesLabel.ForeColor = Color.Red;
          }
        }
      }
    }

    if(printControl.Value is XRChart) {
      var chartItemName = printControl.Key;
      var chartDashboardItem = e.GetDashboardItem(chartItemName) as ChartDashboardItem;
      foreach(var pane in chartDashboardItem.Panes) {
        if(pane.Series.Count > 0) {
          foreach(var dashSeries in pane.Series) {
            if(dashSeries != null) {
              var controlSeries = e.GetChartContext(chartItemName).GetControlSeries(dashSeries);
              if(controlSeries != null) {
                foreach(var ser in controlSeries) {
                  LineSeriesView view = ser.View as LineSeriesView;
                  if(view != null) {
                      view.LineStyle.DashStyle = DashStyle.DashDot;
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Imports DevExpress.DashboardCommon
Imports DevExpress.DashboardWeb
Imports DevExpress.XtraCharts
Imports DevExpress.XtraReports.UI
Imports System
Imports System.Drawing
Imports System.Linq

Protected Sub ASPxDashboard1_CustomExport(ByVal sender As Object, ByVal e As CustomExportWebEventArgs)
  For Each printControl In e.GetPrintableControls()
    If TypeOf printControl.Value Is XRGaugeDashboardItem Then
      Dim gaugeItemName = printControl.Key
      Dim gaugeDashboardItem = TryCast(e.GetDashboardItem(gaugeItemName), GaugeDashboardItem)
      For Each dashGaugeElement In gaugeDashboardItem.Gauges
        For Each gaugePanel In e.GetGaugeContext(gaugeItemName).GetPrintableGauges(dashGaugeElement).Cast(Of XRDashboardGauge)()
          If gaugePanel IsNot Nothing Then
              gaugePanel.MainSeriesLabel.ForeColor = Color.Red
          End If
        Next gaugePanel
      Next dashGaugeElement
    End If

    If TypeOf printControl.Value Is XRChart Then
      Dim chartItemName = printControl.Key
      Dim chartDashboardItem = TryCast(e.GetDashboardItem(chartItemName), ChartDashboardItem)
      For Each pane In chartDashboardItem.Panes
        If pane.Series.Count > 0 Then
          For Each dashSeries In pane.Series
            If dashSeries IsNot Nothing Then
              Dim controlSeries = e.GetChartContext(chartItemName).GetControlSeries(dashSeries)
              If controlSeries IsNot Nothing Then
                For Each ser In controlSeries
                  Dim view As LineSeriesView = TryCast(ser.View, LineSeriesView)
                  If view IsNot Nothing Then
                      view.LineStyle.DashStyle = DashStyle.DashDot
                  End If
                Next ser
              End If
            End If
          Next dashSeries
        End If
      Next pane
    End If
  Next printControl
End Sub

targetWebDashboard.ConfigureItemDataCalculation += Web_ConfigureItemDataCalculation;
    targetWebDashboard.CustomExport += CustomExport;
}

ASPxDashboard1.CustomExport += (s, args) => {
    ChartConstantLinesExtension.CustomExport(args);

AddHandler ASPxDashboard1.CustomExport,
    Sub(s, args)