returning object that caused error to a global errorhandler - vba

Question

i have written the following code which uses a global errorhandler that rectifies the error and resumes code again. right now i have labelled the lines and using 'Erl', i am checking which line caused the error and then accordingly finding the object and creating it.
What i want to do is to pass the object that caused the error to the errorhandler itself and then create that object and return control back to main procedure to resume from where it left off.
How to return the object that caused the error to an error handler? this way it would be more appropriate to handle some errors, instead of just returning an error message and error description.
as an example, i am letting the errorhandler handle creation of sheets if they are non-existent.
Option Explicit
'Worksheets: Public to VBproject as it may be used in almost every module.
Public WSCombined As Worksheet
Public WSResult As Worksheet
'Worksheet names: VBPublic to project as it may be used in almost every module.
Public Const Combined As String = "Combined data"
Public Const Result As String = "Result"
'Array: Public to VBproject as it may be used in almost every module.
Public Arr() As Variant
Sub Main()
On Error GoTo ERRHANDLER
Dim Rng As Range
With ThisWorkbook
'error labels for passing to Erl, so that corresponding sheet names can then be selected for sheet objects.
10001: Set WSCombined = .Sheets(Combined)
10002: Set WSResult = .Sheets(Result)
10003: Set Rng = WSCombined.Rows(1).EntireRow
10004: Arr = Rng
End With
EXITSUB:
' cleanup
Set WSCombined = Nothing
Set WSResult = Nothing
Exit Sub
ERRHANDLER:
If ErrorHandling(Err, ThisWorkbook, Erl) Then
GoTo EXITSUB
Else
Resume
End If
End Sub
Function ErrorHandling(objError As Object, Optional WB As Workbook, Optional ERlCode As Long) As Boolean
With objError
Select Case .Number
Case Is = 9 'subscript out of range
Select Case ERlCode
Case Is = 10001 ' Worksheet: for Combined sheet
Call SheetExists(WB, Combined)
Case Is = 10002 ' Worksheet: for Result sheet
Call SheetExists(WB, Result)
Case Is = 10003 ' Array: Array not initialized
Call IsArrayAllocated(Arr)
Case Else
End Select
ErrorHandling = False ' resume again at same line, after sheet has been created.
Case Is = 91 ' Object variable or with variable not found
Call IsArrayAllocated(Arr)
Case Is = ""
Case Else
MsgBox objError.Number & " - " & objError.Description
ErrorHandling = True
End Select
End With
objError.Clear
On Error GoTo 0
End Function
Function SheetExists(WBook As Workbook, SHTName As String) As Worksheet
On Error GoTo ERRHANDLE
With WBook
Set SheetExists = .Sheets(SHTName)
End With
EXITFUNC:
Exit Function
ERRHANDLE:
With WBook
Dim Sh As Worksheet
Set SheetExists = .Sheets.Add
SheetExists.Name = SHTName
End With
Resume EXITFUNC
End Function
Function IsArrayAllocated(Arr As Variant) As Variant
'Courtesy: #Chip Pearson
' check if array is initialized, if not initialize it
On Error GoTo ERRHANDLE
IsArrayAllocated = (IsArray(Arr) And Not IsError(LBound(Arr, 1)) And LBound(Arr, 1) <= UBound(Arr, 1))
EXITFUNC:
Exit Function
ERRHANDLE:
ReDim Arr(0 To 0)
IsArrayAllocated = Arr
GoTo EXITFUNC
End Function
To tackle some errors, the other way i was thinking is to just have functions created which could have their own error handling code and rectify the error in place itself, instead of passing it to a global error handler of main proc.
e.g.
Sub Main()
On Error GoTo ERRHANDLER
Dim Rng As Range
With ThisWorkbook
set WSCombined = SheetExists(ThisWorkbook, Combined)
Set WSResult = SheetExists(ThisWorkbook, Result)
....
....
Function SheetExists(WBook As Workbook, SHTName As String) As Worksheet
On Error GoTo ERRHANDLE
With WBook
Set SheetExists = .Sheets(SHTName)
End With
EXITFUNC:
Exit Function
ERRHANDLE:
With WBook
Dim Sh As Worksheet
Set SheetExists = .Sheets.Add
SheetExists.Name = SHTName
End With
Resume EXITFUNC
End Function
Any help would be most appreciated.

Answer 1

One answer to your specific question is to use another global object to store the object that threw the error in:
Public LastErrorObject As Object
Sub Main()
With ThisWorkbook
Set LastErrorObject = ThisWorkbook
Set WSCombined = .Sheets(Combined)
End With
End Sub
However, this is incredibly cumbersome, because you need to keep track of it everywhere. Also, it still doesn't do much in the way of giving you the context for the error.
Your second idea is much better, and doesn't abuse the error handler as much because it both acknowleges that there may be an error and actively seeks to avoid errors instead of passively trying to deal with them. For example, instead of indexing into ActiveWorkbook.Worksheets() directly, you can do something like this to make sure you get a new sheet back:
Private Function GetOrCreateWorksheet(book As Workbook, name As String) As Worksheet
On Error GoTo ForceNew
Dim result As Worksheet
Set result = book.Worksheets(name)
ForceNew:
If Err.Number = 9 Then
Set result = book.Worksheets.Add()
result.name = name
ElseIf Err.Number <> 0 Then
Err.Raise Err.Number, Err.source, Err.Description
End If
Set GetOrCreateWorksheet = result
End Function
Note that the error handling is only checking for the one specific error that you'll get if the sheet doesn't exit (Subscript out of range).
BTW and off topic, your Select Case syntax is overly convoluted - you only need to specify the case and can leave out the Is = syntax. It is also much easier to read with another level of indentation:
Select Case ERlCode
Case 10001
'...
Case 10002
'...
Case Else
'...
End Select