Compare Error Handlers in VBA or VB to .NET

Error handling in VBA or VB is done using the On Error statements. While the On Error statements can be used with VB.NET without any problems, it is recommended to utilize Try statements instead. Try statements are more flexibility than the On Error Resume Next and On Error GoTo Label statements.

The use of On Error Resume Next and On Error GoTo Label statements can be rewritten using Try-Catch statements. The following shows how an On Error GoTo Label statement can be rewritten using Try-Catch.

On Error - VBA

Sub ColorEntities()

    On Error GoTo MyErrorHandler

    Dim entry As Object

    For Each entry In ThisDrawing.ModelSpace

        entry.color = acRed

    Next entry

    ' Important! Exit the subroutine before the error handler

  Exit Sub

MyErrorHandler:

    MsgBox entry.EntityName + " is on a locked layer." + _

                              " The handle is: " + entry.Handle

  Resume Next

End Sub

Try-Catch - VB.NET

<CommandMethod("ColorEntities")> _

Public Sub ColorEntities()

  '' 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()

      '' Open the Block table record for read

      Dim acBlkTbl As BlockTable

      acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, _

                                   OpenMode.ForRead)

      '' Open the Block table record Model space for read

      Dim acBlkTblRec As BlockTableRecord

      acBlkTblRec = acTrans.GetObject(acBlkTbl(BlockTableRecord.ModelSpace), _

                                      OpenMode.ForRead)

      Dim acObjId As ObjectId

      '' Step through each object in Model space

      For Each acObjId In acBlkTblRec

Try

              Dim acEnt As Entity

              acEnt = acTrans.GetObject(acObjId, _

                                        OpenMode.ForWrite)

              acEnt.ColorIndex = 1

          Catch

              Application.ShowAlertDialog(acObjId.ObjectClass.DxfName & _

                                          " is on a locked layer." & _

                                          " The handle is: " & acObjId.Handle.ToString())

          End Try

      Next

      acTrans.Commit()

  End Using

End Sub