Revit API Collect All Visible Elements

ElementCollect.cs

using System.Collections.Generic;
using System.Linq;
using Autodesk.Revit.ApplicationServices;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;

namespace ObjExport
{
    internal class ElementCollect
    {
        private readonly UIDocument _uiDocument;
        private readonly Application _app;
        private readonly Document _parentDocument;
        private readonly View _activeView;

        /// <summary>
        /// A class for collecting elements from parent and linked models.
        /// </summary>
        /// <param name="uidoc">The UIDocument instance to operate within.</param>
        internal ElementCollect(UIDocument uidoc)
        {
            _uiDocument = uidoc;
            _app = uidoc.Application.Application;
            _parentDocument = uidoc.Document;
            _activeView = _parentDocument.ActiveView;
        }

        public List<Element> GetVisibleElements()
        {
            VisibleElementContext context = new VisibleElementContext(_parentDocument);
            CustomExporter exp = new CustomExporter(_parentDocument, context);
            List<ElementId> views = new List<ElementId>
            {
                _activeView.Id
            };
            exp.Export(views);

            return context.Elements;
        }
    }

    internal class VisibleElementContext : IExportContext
    {
        public Document ParentDocument;
        public Document CurrentDocument;
        public List<Document> Documents;
        public List<Element> Elements;
        public List<ElementId> ElementIds;

        internal VisibleElementContext(Document doc)
        {
            ParentDocument = doc;
            CurrentDocument = doc;
            Documents = new List<Document> {doc};
            Elements = new List<Element>();
            ElementIds = new List<ElementId>();
        }

        public bool Start()
        {
            return true;
        }

        public void Finish()
        {
        }

        public bool IsCanceled()
        {
            return false;
        }

        public RenderNodeAction OnViewBegin(ViewNode node)
        {
            return RenderNodeAction.Proceed;
        }

        public void OnViewEnd(ElementId elementId)
        {
        }

        public RenderNodeAction OnElementBegin(ElementId elementId)
        {
            ElementIds.Add(elementId);
            Element elem = CurrentDocument.GetElement(elementId);
            Elements.Add(elem);
            return RenderNodeAction.Proceed;
        }

        public void OnElementEnd(ElementId elementId)
        {
        }

        public RenderNodeAction OnInstanceBegin(InstanceNode node)
        {
            return RenderNodeAction.Skip;
        }

        public void OnInstanceEnd(InstanceNode node)
        {
        }

        public RenderNodeAction OnLinkBegin(LinkNode node)
        {
            Document doc = node.GetDocument();
            Documents.Add(doc);
            CurrentDocument = doc;
            return RenderNodeAction.Proceed;
        }

        public void OnLinkEnd(LinkNode node)
        {
            CurrentDocument = ParentDocument;
        }

        public RenderNodeAction OnFaceBegin(FaceNode node)
        {
            return RenderNodeAction.Skip;
        }

        public void OnFaceEnd(FaceNode node)
        {
        }

        public void OnRPC(RPCNode node)
        {
        }

        public void OnLight(LightNode node)
        {
        }

        public void OnMaterial(MaterialNode node)
        {
        }

        public void OnPolymesh(PolymeshTopology node)
        {
        }
    }
}