Excel VBA Event Handlers - vba

Question

1) Can someone please tell me what the issue could be with this code?
2) I need this code actually to run on a worksheet update, but # first-time load of the workbook, i'm running an update using the Workbook_Open event handler. Won't this trigger my Worksheet_Change event as well? Is there any way to avoid this
Private Sub Worksheet_Change(ByVal Target As Range)
Dim ws As Worksheet
Dim rowCount As Integer
Set Worksheet = "datasheet"
Set rowCount = ws.Cells(Rows.Count, "A").End(xlUp)
If Not Intersect(Target, Range("M3:M" & CStr(rowCount))) Is Nothing Then
MsgBox ("Hi")
End If
Else
If Not Intersect(Target, Range("T3:T" & CStr(rowCount))) Is Nothing Then
MsgBox ("Hi")
End If
Else
If Not Intersect(Target, Range("X3:X" & CStr(rowCount))) Is Nothing Then
MsgBox ("Hi")
End If
Else
If Not Intersect(Target, Range("AB3:AB" & CStr(rowCount))) Is Nothing Then
MsgBox ("Hi")
End If
Else
If Not Intersect(Target, Range("AI3:AI" & CStr(rowCount))) Is Nothing Then
MsgBox ("Hi")
End If
End Sub
I'm getting a Compiler error saying "object required" when i change my data with this handler. On the other hand, if i give values instead of taking a rowcount, I get no issues.

Answer 1

I always recommend this when using Worksheet_Change
You do not need the sheet name. It is understood that the code is to be run on current sheet unless you are trying to use another sheet row as a reference as correctly mentioned by brettdj in the comments below.
Whenever you are working with Worksheet_Change event. Always switch Off events if you are writing data to the cell. This is required so that the code doesn't go into a possible endless loop
Whenever you are switching off events, use error handling else if you get an error, the code will not run the next time.
Here is an example
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
On Error GoTo Whoa
Application.EnableEvents = False
'
'~~> Rest of the code
'
LetsContinue:
Application.EnableEvents = True
Exit Sub
Whoa:
MsgBox Err.Description
Resume LetsContinue
End Sub
So using the above, your code becomes (UNTESTED)
Private Sub Worksheet_Change(ByVal Target As Range)
Dim rowCount As Long
On Error GoTo Whoa
Application.EnableEvents = False
With ActiveSheet
rowCount = .Cells(.Rows.Count, "A").End(xlUp).Row
End With
If Not Intersect(Target, Range("M3:M" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("T3:T" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("X3:X" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("AB3:AB" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("AI3:AI" & rowCount)) Is Nothing Then
MsgBox ("Hi")
End If
LetsContinue:
Application.EnableEvents = True
Exit Sub
Whoa:
MsgBox Err.Description
Resume LetsContinue
End Sub
EDIT:
Regarding your 2nd question. As I mentioned in the comment above, you can use a Public variable to check if the worksheet change event is being caused by the workbook open.
Place this code in a module.
Public WasWbOpened As Boolean
Place this code in the workbook code area
Option Explicit
Private Sub Workbook_Open()
WasWbOpened = True
'
'~~> Rest of the code
'
WasWbOpened = False
End Sub
And change your worksheet change event to
Private Sub Worksheet_Change(ByVal Target As Range)
If WasWbOpened = True Then Exit Sub
Dim rowCount As Long
On Error GoTo Whoa
Application.EnableEvents = False
With ActiveSheet
rowCount = .Cells(.Rows.Count, "A").End(xlUp).Row
End With
If Not Intersect(Target, Range("M3:M" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("T3:T" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("X3:X" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("AB3:AB" & rowCount)) Is Nothing Then
MsgBox ("Hi")
ElseIf Not Intersect(Target, Range("AI3:AI" & rowCount)) Is Nothing Then
MsgBox ("Hi")
End If
LetsContinue:
Application.EnableEvents = True
Exit Sub
Whoa:
MsgBox Err.Description
Resume LetsContinue
End Sub

Answer 2

You have several issues
As per Sid's comment you should use rowCount = ws.Cells(ws.Rows.Count, "A").End(xlUp).Row
You should be using Set ws = Sheets("datasheet") not Set Worksheet = "datasheet"
Your Else statements are causing errors as they are orphaned. If you want to exit on the first "Hi" rather than continuing to test you should try something like this
Sid has covered your other point. You can use a Boolean variable for this
updated code
this tests the intersect on columns M, T, X, AB and AI from row 3 to row rowCount in a single line
Private Sub Worksheet_Change(ByVal Target As Range)
Dim ws As Worksheet
Dim rowCount As Long
Set ws = Sheets("datasheet")
rowCount = ws.Cells(Rows.Count, "A").End(xlUp).Row
If Not Intersect(Target, Range("M3:M" & CStr(rowCount) & ",T3:T" & CStr(rowCount) & ",X3:X" & CStr(rowCount) & ",AB3:AB" & CStr(rowCount) & ",AI3:AI" & CStr(rowCount))) Is Nothing Then MsgBox ("Hi")
End Sub