Erase a Member of a Collection Object (.NET)

Members from a collection object can be erased using the Erase method found on the member object. For example, the following code erases the layer MyLayer from the LayerTable object.

Before you erase a layer from a drawing, you should make sure it can be safely removed. To determine if a layer or another named object such as a block or text style can be erased, you should use the Purge method.

VB.NET

Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.DatabaseServices
 
<CommandMethod("RemoveMyLayer")> _
Public Sub RemoveMyLayer()
  '' Get the current document and database, and start a transaction
  Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument
  Dim acCurDb As Database = acDoc.Database
 
  Using acTrans As Transaction = acCurDb.TransactionManager.StartTransaction()
      '' Returns the layer table for the current database
      Dim acLyrTbl As LayerTable
      acLyrTbl = acTrans.GetObject(acCurDb.LayerTableId, _
                                   OpenMode.ForRead)
 
      '' Check to see if MyLayer exists in the Layer table
      If acLyrTbl.Has("MyLayer") = True Then
          Dim acLyrTblRec As LayerTableRecord
          acLyrTblRec = acTrans.GetObject(acLyrTbl("MyLayer"), _
                                          OpenMode.ForWrite)
 
          Try
              acLyrTblRec.Erase()
              acDoc.Editor.WriteMessage(vbLf & "'MyLayer' was erased")
 
              '' Commit the changes
              acTrans.Commit()
          Catch
              acDoc.Editor.WriteMessage(vbLf & "'MyLayer' could not be erased")
          End Try
      Else
          acDoc.Editor.WriteMessage(vbLf & "'MyLayer' does not exist")
      End If
 
      '' Dispose of the transaction
  End Using
End Sub

C#

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
 
[CommandMethod("RemoveMyLayer")]
public static void RemoveMyLayer()
{
  // Get the current document and database, and start a transaction
  Document acDoc = Application.DocumentManager.MdiActiveDocument;
  Database acCurDb = acDoc.Database;
 
  using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
  {
      // Returns the layer table for the current database
      LayerTable acLyrTbl;
      acLyrTbl = acTrans.GetObject(acCurDb.LayerTableId,
                                   OpenMode.ForRead) as LayerTable;
 
      // Check to see if MyLayer exists in the Layer table
      if (acLyrTbl.Has("MyLayer") == true)
      {
          LayerTableRecord acLyrTblRec;
          acLyrTblRec = acTrans.GetObject(acLyrTbl["MyLayer"],
                                          OpenMode.ForWrite) as LayerTableRecord;
 
          try
          {
              acLyrTblRec.Erase();
              acDoc.Editor.WriteMessage("\n'MyLayer' was erased");
 
              // Commit the changes
              acTrans.Commit();
          }
          catch
          {
              acDoc.Editor.WriteMessage("\n'MyLayer' could not be erased");
          }
      }
      else
      {
          acDoc.Editor.WriteMessage("\n'MyLayer' does not exist");
      }
 
      // Dispose of the transaction
  }
}

VBA/ActiveX Code Reference

Sub RemoveMyLayer()
  On Error Resume Next
 
  '' Get the layer "MyLayer" from the Layers collection
  Dim ABCLayer As AcadLayer
  Set ABCLayer = ThisDrawing.Layers.Item("MyLayer")
 
  '' Check for an error, if no error occurs the layer exists
  If Err = 0 Then
 
    '' Delete the layer
    ABCLayer.Delete
 
    '' Clear the current error
    Err.Clear
 
    '' Get the layer again if it is found the layer could not be removed
    Set ABCLayer = ThisDrawing.Layers.Item("MyLayer")
 
    '' Check for error, if an error is encountered the layer was removed
    If Err <> 0 Then
      ThisDrawing.Utility.prompt "'MyLayer' was removed"
    Else
      ThisDrawing.Utility.prompt "'MyLayer' could not be removed"
    End If
  Else
    ThisDrawing.Utility.prompt "'MyLayer' does not exist"
  End If
End Sub

Once an object has been erased, you should not attempt to access the object again later in the program; otherwise an error will occur. The above sample tests to see if the object exists before it is accessed again. When a request to erase an object is made, you should check to see if the object exists with the Has method or use a Try statement to catch any exceptions that occur.

Related Concepts