Occurs when the ReportDataSourceHelper.SetupBeforePrint method is executed.
The BeforeShowPreview event's data class is DevExpress.ExpressApp.ReportsV2.BeforeShowPreviewEventArgs.
Handle this event to modify the report content before it is displayed. For instance, you can merge two reports immediately before they are displayed. An example is provided in the How to: Merge the Pages of Two Reports topic.