Error handling in a loop using Resume Next - excel

Question

as a newcomer to VBA any help would be appreciated. The basic point of my program is to loop through columns of the spreadsheet and count the number of non-blank cells in each column, within a specified range.
Here is an example of what my spreadsheet looks like.
1
2
3
1
thing
2
thing
3
thing
When all the cells in the column are blank, VBA throws out a 1004 error, no cells found. What I want to do is say, if a 1004 error occurs, set the count of the non-blank cells (nonBlank = 0) equal to zero, and if no error occurs, count normally. In something like Python, I'd use try/except. Here is my attempt.
For i = 1 To 3
On Error Resume Next
Set selec_cells = Sheet1.Range(Sheet1.Cells(FirstRow, i), Sheet1.Cells(LastRow, i)).SpecialCells(xlCellTypeVisible).Cells.SpecialCells(xlCellTypeConstants)
If Err.Number <> 1004 Then
nonBlank = 0
Else
nonBlank = selec_cells.Count
End If
On Error GoTo -1
Next i
My issue is, when I run this code, it spits out 0 every time, even though column 2 should return 3. Thank you!
Edit: selec_cells is what throws out the error.

Answer 1

Error Handling
There is no On Error Goto -1 in VBA, it's a VB thing (those are links to different pages). A tip would be if you google VBA stuff, just put VBA in front of what you're looking for.
When using On Error Resume Next (defer error trapping), you should 'apply' it on a line or two maximally and 'close' with On Error Goto 0 (disable error trapping) or with another error handler.
Your usage of On Error Resume Next is unacceptable because in this particular case we can test the range: 1. defer error handling, 2. try to set the range, 3. disable error handling. If there was an error the range will not be set hence If Not rg Is Nothing Then which could be translated to something like 'If rg Is Something Then' (double negation) or If a reference to a range has been created Then.
The second solution illustrates a case where the main error handler is handling all errors except the SpecialCells error which has its own error handler. Resume Next means continue with the line after the line where the error occurred. Note the Exit Sub line and note Resume ProcExit where the code is redirected to a label.
The following illustrates two ways how you could handle this. At this stage, I would suggest you use the first one and remember to use the 'closing' On Error Goto 0 whenever you use On Error Resume Next (a line or two).
The Code
Option Explicit
Sub testOnErrorResumeNext()
Const FirstRow As Long = 2
Const LastRow As Long = 11
Dim rg As Range ' ... additionally means 'Set rg = Nothing'.
Dim nonBlank As Long ' ... additionally means 'nonBlank = 0'.
Dim j As Long
For j = 1 To 3 ' Since it's a column counter, 'j' or 'c' seems preferred.
' Since you're in a loop, you need the following line.
Set rg = Nothing
On Error Resume Next
Set rg = Sheet1.Range(Sheet1.Cells(FirstRow, j), _
Sheet1.Cells(LastRow, j)).SpecialCells(xlCellTypeVisible) _
.Cells.SpecialCells(xlCellTypeConstants)
On Error GoTo 0
If Not rg Is Nothing Then
nonBlank = rg.Cells.Count
Else
' Since you're in a loop, you need the following line.
nonBlank = 0
End If
Debug.Print nonBlank
Next j
End Sub
Sub testOnError()
On Error GoTo clearError
Const FirstRow As Long = 2
Const LastRow As Long = 11
Dim rg As Range ' ... additionally means 'Set rg = Nothing'.
Dim nonBlank As Long ' ... additionally means 'nonBlank = 0'.
Dim j As Long
For j = 1 To 3 ' Since it's a column counter, 'j' or 'c' seems preferred.
' Since you're in a loop, you need the following line.
Set rg = Nothing
On Error GoTo SpecialCellsHandler
Set rg = Sheet1.Range(Sheet1.Cells(FirstRow, j), _
Sheet1.Cells(LastRow, j)).SpecialCells(xlCellTypeVisible) _
.Cells.SpecialCells(xlCellTypeConstants)
On Error GoTo clearError
If Not rg Is Nothing Then
nonBlank = rg.Cells.Count
End If
Debug.Print nonBlank
Next j
ProcExit:
Exit Sub ' Note this.
SpecialCellsHandler:
' Since you're in a loop, you need the following line.
nonBlank = 0
Resume Next
clearError:
MsgBox "Run-time error '" & Err.Number & "': " & Err.Description
Resume ProcExit
End Sub

Answer 2

My preference is, wherever possible, to encapsulate the line of code that may cause an error in its own function. The function returns true or false to indicate whether or not there is an error and an out parameter is used to return the value that you want.
This keeps the error testing confined within a very short well defined function.
Sub ttest()
Dim mySheet As Excel.Worksheet
Set mySheet = ThisWorkbook.Sheet1
Dim myIndex As Long
Dim myNonBlank as long
For myIndex = 1 To 3
If AllCellsAreBlank(mySheet.Range(ThisWorkbook.Sheet1.Cells(myFirstRow, myIndex), mySheet.Cells(myLastRow, myIndex)), myIndex, mySelectCells) Then
myNonBlank = 0
Else
myNonBlank = mySelectCells.Count
End If
Next
End Sub
Public Function AllCellsAreBlank(ByRef ipRange As Excel.Range, ByVal ipIndex As Long, ByRef opSelectCells As Range) As Boolean
On Error Resume Next
set opSelectCells = ipRange.SpecialCells(xlCellTypeVisible).Cells.SpecialCells(xlCellTypeConstants)
AllCellsAreBlank = Err.Number <> 0
On Error GoTo 0
End Function
For reference the prefixes I use are
ip: for an input only parameter
iop: for an input parameters that will be changed by the method
op: for a parameter only used to return a value
my: any variable declared within a Method.
I's also suggest you acquire the habit of meaningful descriptive names, myRow, myCol are much more meaningful than i,j, and of ensuring you use fully qualified references rather than the implicit use of the activesheet.