Purge Unreferenced Named Objects

Unreferenced named objects can be purged from a database at any time. You cannot purge named objects that are referenced by other objects. For example, a font file might be referenced by a text style or a layer might be referenced by the objects on that layer. Purging reduces the size of a drawing file when saved to disk.

Unreferenced objects are purged from a drawing database with the Purge method. The Purge method requires a list of objects you want to purge in the form of an ObjectIdCollection or ObjectIdGraph objects. The ObjectIdCollection or ObjectIdGraph objects passed into the Purge method are updated with the objects in which can be erased from the database. After the call to Purge, you must erase each individual object returned.

VBA/ActiveX Cross Reference

Purge all unreferenced layers

The following example demonstrates how to purge all unreferenced layers from a database.

VB.NET

Imports Autodesk.AutoCAD.Runtime

Imports Autodesk.AutoCAD.ApplicationServices

Imports Autodesk.AutoCAD.DatabaseServices

<CommandMethod("PurgeUnreferencedLayers")> _

Public Sub PurgeUnreferencedLayers()

  '' Get the current document and database

  Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument

  Dim acCurDb As Database = acDoc.Database

  '' Start a transaction

  Using acTrans As Transaction = acCurDb.TransactionManager.StartTransaction()

      '' Open the Layer table for read

      Dim acLyrTbl As LayerTable

      acLyrTbl = acTrans.GetObject(acCurDb.LayerTableId, _

                                   OpenMode.ForRead)

      '' Create an ObjectIdCollection to hold the object ids for each table record

      Dim acObjIdColl As ObjectIdCollection = New ObjectIdCollection()

      '' Step through each layer and add it to the ObjectIdCollection

      For Each acObjId As ObjectId In acLyrTbl

          acObjIdColl.Add(acObjId)

      Next

      '' Remove the layers that are in use and return the ones that can be erased

      acCurDb.Purge(acObjIdColl)

      '' Step through the returned ObjectIdCollection

      For Each acObjId As ObjectId In acObjIdColl

          Dim acSymTblRec As SymbolTableRecord

          acSymTblRec = acTrans.GetObject(acObjId, _

                                          OpenMode.ForWrite)

Try

              '' Erase the unreferenced layer

              acSymTblRec.Erase(True)

          Catch Ex As Autodesk.AutoCAD.Runtime.Exception

              '' Layer could not be deleted

              Application.ShowAlertDialog("Error:" & vbLf & Ex.Message)

          End Try

      Next

      '' Commit the changes and dispose of the transaction

      acTrans.Commit()

  End Using

End Sub

using Autodesk.AutoCAD.Runtime;

using Autodesk.AutoCAD.ApplicationServices;

using Autodesk.AutoCAD.DatabaseServices;

[CommandMethod("PurgeUnreferencedLayers")]

public static void PurgeUnreferencedLayers()

  // Get the current document and database

  Document acDoc = Application.DocumentManager.MdiActiveDocument;

  Database acCurDb = acDoc.Database;

  // Start a transaction

  using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())

      // Open the Layer table for read

      LayerTable acLyrTbl;

      acLyrTbl = acTrans.GetObject(acCurDb.LayerTableId,

                                   OpenMode.ForRead) as LayerTable;

      // Create an ObjectIdCollection to hold the object ids for each table record

      ObjectIdCollection acObjIdColl = new ObjectIdCollection();

      // Step through each layer and add iterator to the ObjectIdCollection

      foreach (ObjectId acObjId in acLyrTbl)

          acObjIdColl.Add(acObjId);

      // Remove the layers that are in use and return the ones that can be erased

      acCurDb.Purge(acObjIdColl);

      // Step through the returned ObjectIdCollection

      // and erase each unreferenced layer

      foreach (ObjectId acObjId in acObjIdColl)

          SymbolTableRecord acSymTblRec;

          acSymTblRec = acTrans.GetObject(acObjId,

                                          OpenMode.ForWrite) as SymbolTableRecord;

try

              // Erase the unreferenced layer

              acSymTblRec.Erase(true);

          catch (Autodesk.AutoCAD.Runtime.Exception Ex)

              // Layer could not be deleted

              Application.ShowAlertDialog("Error:\n" + Ex.Message);

      // Commit the changes and dispose of the transaction

      acTrans.Commit();