Find an existing layer

Before I get to creating new layers, I thought I'd spend a moment on checking if a layer already exists. After all, we can't make a layer if it's already there.

  Public Function LayerExists(ByRef oDb As Database, _

                              ByRef oTrans As Transaction, _

                              ByVal strName As String) As Boolean

    ' Create a layer object

    Dim oLayer As LayerTableRecord

 

    ' Set our return value to nothing

    Dim retValue As Boolean = False

 

    Try

      ' Open up the layer table (for reading)

      Dim oLayerTable As LayerTable = CType(oTrans.GetObject(oDb.LayerTableId, _

                                                            OpenMode.ForRead, _

                                                            False), _

                                            LayerTable)

 

      ' Loop through each object in the layer table

      For Each objId As ObjectId In oLayerTable

        ' Get the layertablerecord object for the current id

        oLayer = CType(oTrans.GetObject(objId, _

                                        OpenMode.ForWrite), _

                      LayerTableRecord)

 

        ' Compare the layer name to the strName variable and

        ' make sure we're not checking erased layers

        If oLayer.Name.ToUpper.Equals(strName.ToUpper) And _

          Not oLayer.IsErased Then

          ' Found the layer

          retValue = True

          Exit For

        End If

      Next

    Catch ex As System.Exception

      MsgBox(ex.Message, MsgBoxStyle.Exclamation, "Error in LayerExists")

    End Try

 

    Return retValue

  End Function