Dummy Revit Custom Exporter - This sample runs a dummy exporter to test if current Revit 3D view can be exported without any errors. It won't produce any files, just run the export API.

DummyExportContext.cs

// (C) Copyright 2022 by Autodesk, Inc. 
//
// Permission to use, copy, modify, and distribute this software
// in object code form for any purpose and without fee is hereby
// granted, provided that the above copyright notice appears in
// all copies and that both that copyright notice and the limited
// warranty and restricted rights notice below appear in all
// supporting documentation.
//
// AUTODESK PROVIDES THIS PROGRAM "AS IS" AND WITH ALL FAULTS. 
// AUTODESK SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTY OF
// MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE.  AUTODESK,
// INC. DOES NOT WARRANT THAT THE OPERATION OF THE PROGRAM WILL
// BE UNINTERRUPTED OR ERROR FREE.
//
// Use, duplication, or disclosure by the U.S. Government is
// subject to restrictions set forth in FAR 52.227-19 (Commercial
// Computer Software - Restricted Rights) and DFAR 252.227-7013(c)
// (1)(ii)(Rights in Technical Data and Computer Software), as
// applicable.
//

using Autodesk.Revit.DB;

namespace ExportTest
{
    class DummyExportContext : IExportContext
    {
        private Document document;
        public ElementId CurrentElementId { get; private set; }
        public DummyExportContext(Document document)
        {
            this.document = document;
        }

        public void Finish()
        {
            System.Diagnostics.Trace.WriteLine("Finish");
        }

        public bool IsCanceled()
        {
            return false;
        }

        public RenderNodeAction OnElementBegin(ElementId elementId)
        {
            Element e = this.document.GetElement(elementId);
            string uid = e.UniqueId;
            this.CurrentElementId = e.Id;

            System.Diagnostics.Trace.WriteLine(string.Format(
              "OnElementBegin: id {0} category {1} name {2}",
              elementId.IntegerValue, e.Category.Name, e.Name));

            return RenderNodeAction.Proceed;
        }

        public void OnElementEnd(ElementId id)
        {
            Element e = this.document.GetElement(id);
            string uid = e.UniqueId;

            System.Diagnostics.Trace.WriteLine(string.Format(
              "OnElementEnd: id {0} category {1} name {2}",
              id.IntegerValue, e.Category.Name, e.Name));

            this.CurrentElementId = null;
        }

        public RenderNodeAction OnFaceBegin(FaceNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnFaceBegin: " + node.NodeName);
            return RenderNodeAction.Proceed;
        }

        public void OnFaceEnd(FaceNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnFaceEnd: " + node.NodeName);
        }

        public RenderNodeAction OnInstanceBegin(InstanceNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnInstanceBegin: " + node.NodeName
                + " symbol: " + node.GetSymbolId().IntegerValue);

            var symId = node.GetSymbolId();

            // We can either skip this instance or proceed with rendering it.
            return RenderNodeAction.Proceed;
        }

        public void OnInstanceEnd(InstanceNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnInstanceEnd: " + node.NodeName);
        }

        public void OnLight(LightNode node)
        {
            System.Diagnostics.Trace.WriteLine("OnLight: " + node.NodeName);
        }

        public RenderNodeAction OnLinkBegin(LinkNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnLinkBegin: " + node.NodeName + " Document: " + node.GetDocument().Title + ": Id: " + node.GetSymbolId().IntegerValue);
            return RenderNodeAction.Proceed;
        }

        public void OnLinkEnd(LinkNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnLinkEnd: " + node.NodeName);
        }

        public void OnMaterial(MaterialNode node)
        {
            System.Diagnostics.Trace.WriteLine("  OnMaterial: " + node.NodeName);
        }

        public void OnPolymesh(PolymeshTopology node)
        {
            System.Diagnostics.Trace.WriteLine("  OnPolymesh: ");
            var dNormals = node.DistributionOfNormals;
            var nFaces = node.NumberOfFacets;
            var nNormals = node.NumberOfNormals;
            var nPts = node.NumberOfPoints;
            var nUV = node.NumberOfUVs;
        }

        public void OnRPC(RPCNode node)
        {
            System.Diagnostics.Trace.WriteLine("OnRPC: " + node.NodeName);
        }

        public RenderNodeAction OnViewBegin(ViewNode node)
        {
            System.Diagnostics.Trace.WriteLine("OnViewBegin: "
                + node.NodeName + "(" + node.ViewId.IntegerValue
                + "): LOD: " + node.LevelOfDetail);

            return RenderNodeAction.Proceed;
        }

        public void OnViewEnd(ElementId elementId)
        {
            Element e = this.document.GetElement(elementId);
            string uid = e.UniqueId;

            System.Diagnostics.Trace.WriteLine(string.Format(
                "OnElementBegin: id {0} category {1} name {2}",
                elementId.IntegerValue, e.Category.Name, e.Name));
        }

        public bool Start()
        {
            return true;
        }
    }
}

ExportCommand.cs

// (C) Copyright 2022 by Autodesk, Inc. 
//
// Permission to use, copy, modify, and distribute this software
// in object code form for any purpose and without fee is hereby
// granted, provided that the above copyright notice appears in
// all copies and that both that copyright notice and the limited
// warranty and restricted rights notice below appear in all
// supporting documentation.
//
// AUTODESK PROVIDES THIS PROGRAM "AS IS" AND WITH ALL FAULTS. 
// AUTODESK SPECIFICALLY DISCLAIMS ANY IMPLIED WARRANTY OF
// MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE.  AUTODESK,
// INC. DOES NOT WARRANT THAT THE OPERATION OF THE PROGRAM WILL
// BE UNINTERRUPTED OR ERROR FREE.
//
// Use, duplication, or disclosure by the U.S. Government is
// subject to restrictions set forth in FAR 52.227-19 (Commercial
// Computer Software - Restricted Rights) and DFAR 252.227-7013(c)
// (1)(ii)(Rights in Technical Data and Computer Software), as
// applicable.
//

using System;
using Autodesk.Revit.Attributes;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;

namespace ExportTest
{
    [Transaction(TransactionMode.Manual)]
    public class ExportCommand : IExternalCommand
    {
        public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
        {
            var document = commandData.Application.ActiveUIDocument.Document;
            var view = commandData.Application.ActiveUIDocument.ActiveView;
            var exportContext = new DummyExportContext(document);

            var exporter = new CustomExporter(document, exportContext);

            exporter.ShouldStopOnError = true;

            try
            {
                exporter.Export(view);
            }
            catch(Exception ex)
            {
                var msg = string.Format("Failed to proccess the geometries of Element Id `{0}`", exportContext.CurrentElementId);
                System.Diagnostics.Trace.WriteLine(msg);
                TaskDialog.Show("Revit", msg);
            }

            return Result.Succeeded;
        }
    }
}