VBA error handling query - vba

Question

I was hoping someone could have a look and tidy this up for me; I have to say error handling is not strong point of mine. I have the code block below and I have been playing around with some error handles but it is not as I really want it.
What I am trying to do is ensure that if at any point there is an error the workbook and excel instance I have opened are closed down gracefully.
I am sure there are much nicer and simpler ways to achieve this than what I have come up with.
Sub QOScode()
On Error GoTo Fail
Dim app As New Excel.Application
app.Visible = False 'Visible is False by default, so this isn't necessary
Dim book As Excel.Workbook
Set book = app.Workbooks.Add(ActiveWorkbook.Path & "\QOS DGL stuff.xlsx")
'set up error handeling so if any thing happens the instance of excel with QOS sheets is closed gracefully
On Error GoTo Closebook
' MsgBox book.Sheets("ACLS").Cells(3, 3)
'Do what you have to do
'
Closebook:
On Error Resume Next
book.Close SaveChanges:=False
app.Quit
Set app = Nothing
On Error GoTo 0
Fail:
End Sub
What I want is a single On error - close app and exit sub.
Can anyone provide a sample of what would be considered best practice for doing this?
Cheers
Aaron
So this code below, when the sheet does not exist it will cause the error, why does it not skip the "book.close" statement, I know this throws an error, but I want it to ignore it?
Sub QOScode()
On Error GoTo Closebook
Dim app As New Excel.Application
app.Visible = False
Dim book As Excel.Workbook
Set book = app.Workbooks.Add(ActiveWorkbook.Path & "\QOaS DGL stuff.xlsx") 'this sheet does not exist
'
MsgBox book.Sheets("ACLS").Cells(3, 3)
'Do what you have to do
'
Closebook:
Err.Clear
On Error Resume Next
book.Close SaveChanges:=False 'Object variable or with block variable not set (error 91)
app.Quit
Set app = Nothing
On Error GoTo 0
End Sub

Answer 1

My 2 cents on Error Handling.
You should always do error handling.
Some of the Reasons
1) You wouldn't want your app to break down and leave your users hanging! Imagine the frustration that it would cause them.
2) Error handling doesn't mean that you are trying to ignore error.
3) Error handling is neither defensive programming or aggressive programming. IMHO it is proactive programming.
4) Very few people are aware that you can find out the line which is causing the error. The property that I am talking about is ERL. Consider this example
Sub Sample()
Dim i As Long
Dim j As Long, k As Long
10 On Error GoTo Whoa
20 i = 5
30 j = "Sid"
40 k = i * j
50 MsgBox k
60 Exit Sub
Whoa:
70 MsgBox "Description : " & Err.Description & vbNewLine & _
"Error Number : " & Err.Number & vbNewLine & _
"Error at Line: " & Erl
End Sub
5) In subs like worksheet change event, it is a must to do error handling. Imagine you have set the Enable Event to False and your code breaks! The code won't run next time till you set the events back to true
6) I can go on and on :-) Would recommend this link
Topic: To ‘Err’ is Human
Link: http://www.siddharthrout.com/2011/08/01/to-err-is-human/
Tip:
Use MZ Tools. It is free!
Here is how I would write your code.
Sub QOScode()
Dim app As New Excel.Application
Dim book As Excel.Workbook
10 On Error GoTo Whoa
20 Set book = app.Workbooks.Open(ActiveWorkbook.Path & "\QOS DGL stuff.xlsx")
30 MsgBox book.Sheets("ACLS").Cells(3, 3)
'
'Do what you have to do
'
LetsContinue:
40 On Error Resume Next
50 book.Close SaveChanges:=False
60 Set book = Nothing
70 app.Quit
80 Set app = Nothing
90 On Error GoTo 0
100 Exit Sub
Whoa:
110 MsgBox "Description : " & Err.Description & vbNewLine & _
"Error Number : " & Err.Number & vbNewLine & _
"Error at Line: " & Erl
120 Resume LetsContinue
End Sub

Answer 2

I am not quite sure I understand your objective. If I did, I would probably disagree.
Is this code you are developing? I almost never use error handling in code I am developing. I want the interpreter to stop on the statement that gives the error. I want to understand why that error has occurred. What could I have done to avoid the error? Did I fail to check the file exists? Did I fail to check the path is accessable? I will add the missing code before I do anything else.
By the time you have finished development, you should plan for there to be no error condition for which you have not included proper code. Of course, this is impossible; you cannot make your code foolproof because fools are so ingenious. The version you release to users must contains error handling.
But you could not release this code to users since it would stop without warning. Would the user guess something had gone wrong with the macro or would they assume this was what was supposed to happen? If they decide the macro has failed what are they going to say to you? "It did not do what I was expecting and I do not know why." What are you going to say back? "What were you doing?" I do not think I have ever had a user give a believable description of what they were doing at the time of a failure. At the very least you want:
Call MsgBox("Sorry I have had an unrecoverable error within QOScode()." & _
" Please record: " & Err.Number & " " & Err.Description & _
" and report to extension 1234")
With this, the user does not wonder if something has gone wrong and you know where it went wrong and, with luck, why.

Answer 3

To handle the foreseen issue neatly you can use short error handling to test that the Workbook actually exists (ie If Not Wb Is Nothing Then, if so work on it, with a common ending (ie destroying the object)
The second sample shows how to add additional handling for unforeseen errors once the workbook has been opened.I have used Err.Raise to create deliberate error to give the user a choice as to how to proceed (close the workbook immediately post error or make the workbook visible)
As an aside, don't use Dim and New together. I have re-written
Dim app As New Excel.Application
into
Dim xlApp As Excel.Application
Set xlApp = New Excel.Application
1. Handling the no workbook issue
Sub QOScode()
Dim xlApp As Excel.Application
Set xlApp = New Excel.Application
Dim Wb As Excel.Workbook
On Error Resume Next
Set Wb = xlApp.Workbooks.Add(ActiveWorkbook.Path & "\QOaS DGL stuff.xlsx") 'this sheet does not exist
On Error GoTo 0 '
If Not Wb Is Nothing Then
MsgBox Wb.Sheets("ACLS").Cells(3, 3)
'Do what you have to do
Wb.Close False
End If
xlApp.Quit
Set xlApp = Nothing
End Sub
2. Handling no workbook and other unforseen error which may otherwise leave the worbook open
Sub QOScode2()
Dim xlApp As Excel.Application
Set xlApp = New Excel.Application
Dim Wb As Excel.Workbook
Dim lngChk As Long
On Error Resume Next
Set Wb = xlApp.Workbooks.Add(ActiveWorkbook.Path & "\QOaS DGL stuff.xlsx") 'this sheet does not exist
On Error GoTo 0 '
If Not Wb Is Nothing Then
On Error GoTo ProblemHandler
MsgBox Wb.Sheets("ACLS").Cells(3, 3)
'Do what you have to do
'Deliberate error
Err.Raise 2000, "test code", "Sample Error"
Wb.Close False
Else
MsgBox "Workbook not found,code will now exit"
End If
xlApp.Quit
Set xlApp = Nothing
Exit Sub
ProblemHandler:
'Test to see if workbook was still open when error happened
If Not Wb Is Nothing Then
lngChk = MsgBox("The code encountered an error" & vbNewLine & Err.Number & vbNewLine & "Do you want to close the file?", vbYesNo, Err.Description)
If lngChk = vbYes Then
'close book. Code will proceed to destroy app
Wb.Close False
Else
'make workbook visible and leave code
Wb.Visible = True
Exit Sub
End If
Else
MsgBox "The code encountered an error - the file was already closed at this point" & vbNewLine & "Error number " & Err.Number & vbNewLine, Err.Description
End If
'destroy app (either if the workbook was closed, or user chose to close it)
xlApp.Quit
Set xlApp = Nothing
End Sub