Understanding issue with Error Handling in a for loop VBA - vba

Question

I wrote some examples to highlight what my issue in understanding is.
1. Example: This works as expected. The error is getting handled via the Goto Statement and the error handling is returned to normal behavior arfterwards
Sub ErrorHandlingWithoutLoop()
Debug.Print "Before Error"
On Error GoTo errorHandler
Error (1)
' If no Error occured, the ErrorHandling procedure is skipped
GoTo skip
errorHandler:
Debug.Print "Handle Error"
On Error GoTo 0
skip:
Debug.Print "After Error"
'Raise Error to see if error Handling is resumed to normal behavior
Error (14)
End Sub
VBA returns:
Before Error
Handle Error
After Error
And the Error Handling is returned to normal, visible by the thrown error (14)
Example 2: I would expect this sub to run through just fine and just throw an error in the last line with error (14).
However in the second loop with n=2, the error handling doesnt work as intended. Why?
Sub ErrorHandlingWithLoop()
Debug.Print "Before Error"
For n = 1 To 10
On Error GoTo errorHandler
Error (1)
' If no Error occured, the ErrorHandling procedure is skipped
GoTo skip
errorHandler:
Debug.Print "Handle Error", n
On Error GoTo 0
skip:
Debug.Print "After Error", n
Next n
'Raise Error to see if error Handling is resumed to normal behavior
' -> This wont be reached though
Error (14)
End Sub
VBA returns:
Before Error
Handle Error 1
After Error 1
The execution of the code stops in the second loop with n=2 with a thrown error of 1. The Error 14 at the end is not thrown
Example 3: I know I can fix this behaviour by adding a "resume skip" statement. However I dont understand why this is necessary?
Sub ErrorHandlingWithLoopFixed()
Debug.Print "Before Error"
For n = 1 To 10
On Error GoTo errorHandler
Error (1)
' If no Error occured, the ErrorHandling procedure is skipped
GoTo skip
errorHandler:
Debug.Print "Handle Error", n
On Error GoTo 0
Resume skip
skip:
Debug.Print "After Error", n
Next n
'Raise Error to confirm that error Handling is resumed to normal behavior
Error (14)
End Sub
VBA returns:
Before Error
Handle Error 1
After Error 1
Handle Error 2
After Error 2
Handle Error 3
After Error 3
Handle Error 4
After Error 4
Handle Error 5
After Error 5
Handle Error 6
After Error 6
Handle Error 7
After Error 7
Handle Error 8
After Error 8
Handle Error 9
After Error 9
Handle Error 10
After Error 10
And the Error Handling is returned to normal, visible by the thrown error (14)
So why is the Resume skip necessary?!
Thanks for any help=)
Edit:
!Bonus Example!3: Interestingly, if I add a On Error Goto -1, then the for-loop loops infinitely. Why is that? I cant make a rhyme of that...
Sub ErrorHandlingWithLoop()
Debug.Print "Before Error"
For n = 1 To 10
On Error GoTo errorHandler
Error (1)
' If no Error occured, the ErrorHandling procedure is skipped
GoTo skip
errorHandler:
Debug.Print "Handle Error", n
On Error GoTo -1
skip:
Debug.Print "After Error", n
Next n
'Raise Error to see if error Handling is resumed to normal behavior
' -> This wont be reached though
Error (14)
End Sub
VBA returns:
Before Error
Handle Error 1
After Error 1
Handle Error 2
After Error 2
Handle Error 3
After Error 3
Handle Error 4
After Error 4
Handle Error 5
After Error 5
Handle Error 6
After Error 6
Handle Error 7
After Error 7
Handle Error 8
...
...
...
This continues on and on until Excel crashes.
Any help on this as well?

Answer 1

Personally, I would not follow the example you provide to deal with error handling. Instead I would encapsulate the action that might result in an error in its own function which returns true or false depending on whether or not the action was successful or not. The value returned by the action is passed out of the function using a ByRef parameter.
Sub ErrorHandlingWithLoopFixed()
Debug.Print "Before Error"
Dim myResult as Variant
For n = 1 To 10
If Not TryAction( myResult) then
Debug.Print "An error occurred"
Stop ' or exit function or whatever
end if
' Continue processing myResult
Next n
'Raise Error to confirm that error Handling is resumed to normal behavior
Error (14)
End Sub
Public Function TryAction( ByRef opResult) as Boolean
On Error Resume Next
opResult = ' the action
TryAction = err.number = 0
On Error Goto 0
Exit Function
As you can see from above, the code is much easier to follow and there are no problems with jumping in and out of the scope of a For loop.

Answer 2

For example 2: the reason you need Resume skip is that an error handler only "handles" once and gets deactivated. After that you must activate it again which is exactly what resume does.
Paul Kelly names this: "reseting the mouse trap", because like a mouse trap an error handler gets deactivated when used, and you need to activate it manually for it to work again.
All these can perform that task (activate the mouse trap): resume label, resume next, on error goto -1. Also On Error Resume Next takes care of the reactivation itself (you don't need to do it manually for that one).
For the bonus the reason for the infinite loop is that you have an error right befor the end, but no Exit Sub before it. So whenever you reach that error you'll be thrown back in the error handler, which you've put in the loop. A safer way is to have your error handlers at the end, after an exit sub.