public class Application_DocumentPrinting : IExternalApplication
{
    /// <ExampleMethod>
    /// <summary>
    /// Implement the OnStartup method to register events when Revit starts.
    /// </summary>
    public Result OnStartup(UIControlledApplication application)
    {
        // Register related events
       application.ControlledApplication.DocumentPrinting += new EventHandler<Autodesk.Revit.DB.Events.DocumentPrintingEventArgs>(AppDocumentPrinting);
        return Result.Succeeded;
    }

    /// <summary>
    /// Implement this method to unregister the subscribed events when Revit exits.
    /// </summary>
    public Result OnShutdown(UIControlledApplication application)
    {
        // unregister events
       application.ControlledApplication.DocumentPrinting -= new EventHandler<Autodesk.Revit.DB.Events.DocumentPrintingEventArgs>(AppDocumentPrinting);
        return Result.Succeeded;
    }
    /// <TrivialCode>
    /// Code ID: 501
    /// For DocumentPrinting class description
    /// </TrivialCode>


    /// <summary>
    /// Handler method for DocumentPrinting event, it will display some event arguments.
    /// </summary>
    public void AppDocumentPrinting(object sender, Autodesk.Revit.DB.Events.DocumentPrintingEventArgs args)
    {
        StringBuilder info = new StringBuilder();
        info.AppendLine("DocumentPrintingEventArgs Parameters ------>");

        info.AppendLine("    Event Cancellable   : " + args.Cancellable);
        info.AppendLine("    Views to be printed : "); // Views
        Application app = sender as Application;
        DumpViewsInfo(app, args.GetViewElementIds(), "    ", ref info);

        TaskDialog.Show("Revit",info.ToString());
    }


    /// <summary>
    /// Dump information of views: ViewType, Id and ViewName.
    /// </summary>
    /// <param name="views">Views to be displayed in message box.</param>
    /// <param name="prefix">Prefix mark for each line added to message box.</param>
    /// <param name="info">String where data is stored for display</param>
    private static void DumpViewsInfo(Application app, System.Collections.Generic.IList<ElementId> viewIds, String prefix, ref StringBuilder info)
    {
        int index = 0;
        UIApplication uiApp = new UIApplication(app);
        foreach (ElementId curViewId in viewIds)
        {
            Autodesk.Revit.DB.View curView = uiApp.ActiveUIDocument.Document.GetElement(curViewId) as Autodesk.Revit.DB.View;
            DumpViewInfo(curView, String.Format("{0}#{1}", prefix, index++), ref info);
        }
    }

    /// <summary>
    /// Dump information of single view: ViewType, Id and ViewName.
    /// </summary>
    /// <param name="view">View element to be displayed in message box.</param>
    /// <param name="prefix">Prefix mark for each line sent to message box.</param>
    /// <param name="info">String where data is stored for display</param>
    private static void DumpViewInfo(Autodesk.Revit.DB.View view, String prefix, ref StringBuilder info)
    {
        info.AppendLine(String.Format("{0} Id: {1}, ViewName: {2}, ViewType: {3}",
            prefix, view.Id.IntegerValue, view.Name, view.ViewType));
    }
    /// </ExampleMethod>
}

Public Class Application_DocumentPrinting
    Implements IExternalApplication
    ' <ExampleMethod>
    ' <summary>
    ' Implement the OnStartup method to register events when Revit starts.
    ' </summary>
    Public Function OnStartup(application As UIControlledApplication) As Autodesk.Revit.UI.Result Implements IExternalApplication.OnStartup
        ' Register related events
        AddHandler application.ControlledApplication.DocumentPrinting, AddressOf AppDocumentPrinting
        Return Result.Succeeded
    End Function

    ' <summary>
    ' Implement this method to unregister the subscribed events when Revit exits.
    ' </summary>
    Public Function OnShutdown(application As UIControlledApplication) As Autodesk.Revit.UI.Result Implements IExternalApplication.OnShutdown
        ' unregister events
        RemoveHandler application.ControlledApplication.DocumentPrinting, AddressOf AppDocumentPrinting
        Return Result.Succeeded
    End Function
    ' <TrivialCode>
    ' Code ID: 501
    ' For DocumentPrinting class description
    ' </TrivialCode>



    ' <summary>
    ' Handler method for DocumentPrinting event, it will display some event arguments.
    ' </summary>
    Public Sub AppDocumentPrinting(sender As Object, args As Autodesk.Revit.DB.Events.DocumentPrintingEventArgs)
        Dim info As New StringBuilder()
        info.AppendLine("DocumentPrintingEventArgs Parameters ------>")

        info.AppendLine("    Event Cancellable   : " & Convert.ToString(args.Cancellable))
        info.AppendLine("    Views to be printed : ")
        ' Views
        Dim app As Application = TryCast(sender, Application)
        DumpViewsInfo(app, args.GetViewElementIds(), "    ", info)

        TaskDialog.Show("Revit", info.ToString())
    End Sub


    ' <summary>
    ' Dump information of views: ViewType, Id and ViewName.
    ' </summary>
    ' <param name="views">Views to be displayed in message box.</param>
    ' <param name="prefix">Prefix mark for each line added to message box.</param>
    ' <param name="info">String where data is stored for display</param>
    Private Shared Sub DumpViewsInfo(app As Application, viewIds As System.Collections.Generic.IList(Of ElementId), prefix As [String], ByRef info As StringBuilder)
        Dim index As Integer = 0
        Dim uiApp As New UIApplication(app)
        For Each curViewId As ElementId In viewIds
            Dim curView As Autodesk.Revit.DB.View = TryCast(uiApp.ActiveUIDocument.Document.GetElement(curViewId), Autodesk.Revit.DB.View)
            DumpViewInfo(curView, [String].Format("{0}#{1}", prefix, System.Math.Max(System.Threading.Interlocked.Increment(index), index - 1)), info)
        Next
    End Sub

    ' <summary>
    ' Dump information of single view: ViewType, Id and ViewName.
    ' </summary>
    ' <param name="view">View element to be displayed in message box.</param>
    ' <param name="prefix">Prefix mark for each line sent to message box.</param>
    ' <param name="info">String where data is stored for display</param>
    Private Shared Sub DumpViewInfo(view As Autodesk.Revit.DB.View, prefix As [String], ByRef info As StringBuilder)
        info.AppendLine([String].Format("{0} Id: {1}, ViewName: {2}, ViewType: {3}", prefix, view.Id.IntegerValue, view.Name, view.ViewType))
    End Sub
    ' </ExampleMethod>
End Class