Detect whether cell value was actually changed by editing - vba

Question

Worksheet_Change triggers when a cell value is changed (which is what I want), but it also triggers when you enter a cell as if to edit it but don't actually change the cell's value (and this is what I don't want to happen).
Say I want to add shading to cells whose value was changed. So I code this:
Private Sub Worksheet_Change(ByVal Target As Range)
Target.Interior.ColorIndex = 36
End Sub
Now to test my work: Change cell A1 and the cell gets highlighted. That's the desired behaviour. So far so good. Then, double click B1 but don't change the value there and then click C1. You'll notice B1 gets highlighted! And this is not the desired behaviour.
Do I have to go through the methods discussed here of capturing the old value, then compare old to new before highlighting the cell? I certainly hope there's something I'm missing.

Answer 1

I suggest automatically maintaining a "mirror copy" of your sheet, in another sheet, for comparison with the changed cell's value.
#brettdj and #JohnLBevan essentially propose doing the same thing, but they store cell values in comments or a dictionary, respectively (and +1 for those ideas indeed). My feeling, though, is that it is conceptually much simpler to back up cells in cells, rather than in other objects (especially comments, which you or the user may want to use for other purposes).
So, say I have Sheet1 whose cells the user may change. I created this other sheet called Sheet1_Mirror (which you could create at Workbook_Open and could set to be hidden if you so desire -- up to you). To start with, the contents of Sheet1_Mirror would be identical to that of Sheet1 (again, you could enforce this at Workbook_Open).
Every time Sheet1's Worksheet_Change is triggered, the code checks whether the "changed" cell's value in Sheet1 is actually different from that in Sheet1_Mirror. If so, it does the action you want and updates the mirror sheet. If not, then nothing.
This should put you on the right track:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim r As Range
For Each r In Target.Cells
'Has the value actually changed?
If r.Value <> Sheet1_Mirror.Range(r.Address).Value Then
'Yes it has. Do whatever needs to be done.
MsgBox "Value of cell " & r.Address & " was changed. " & vbCrLf _
& "Was: " & vbTab & Sheet1_Mirror.Range(r.Address).Value & vbCrLf _
& "Is now: " & vbTab & r.Value
'Mirror this new value.
Sheet1_Mirror.Range(r.Address).Value = r.Value
Else
'It hasn't really changed. Do nothing.
End If
Next
End Sub

Answer 2

This code uses Comments to store the prior value (Please note if you do need the comments for other purposes this method will remove them)
Cells that have no value have colour reset to xlNone
An intial value typed into a cell is blue (ColorIndex 34)
If the value is changed the cell goes from blue to yellow
Normal module - turn display of comments off
Sub SetCom()
Application.DisplayCommentIndicator = xlNoIndicator
End Sub
Sheet code to capture changes
Private Sub Worksheet_Change(ByVal Target As Range)
Dim rng1 As Range
Dim shCmt As Comment
For Each rng1 In Target.Cells
If Len(rng1.Value) = 0 Then
rng1.Interior.ColorIndex = xlNone
On Error Resume Next
rng1.Comment.Delete
On Error GoTo 0
Else
On Error Resume Next
Set shCmt = rng1.Comment
On Error GoTo 0
If shCmt Is Nothing Then
Set shCmt = rng1.AddComment
shCmt.Text Text:=CStr(rng1.Value)
rng1.Interior.ColorIndex = 34
Else
If shCmt.Text <> rng1.Value Then
rng1.Interior.ColorIndex = 36
shCmt.Text Text:=CStr(rng1.Value)
End If
End If
End If
Next
End Sub

Answer 3

Try this code. When you enter a range it stores the original cell values in a dictionary object. When the worksheet change is triggered it compares the stored values with the actuals and highlights any changes.
NB: to improve efficiency reference microsoft scripting runtime & replace the As Object with As Scripting.Dictionary and the CreateObject("Scripting.Dictionary") with New Scripting.Dictionary.
Option Explicit
Private previousRange As Object 'reference microsoft scripting runtime & use scripting.dictionary for better performance
'I've gone with late binding to avoid references from confusing the example
Private Sub Worksheet_Change(ByVal Target As Range)
Dim cell As Variant
For Each cell In Target
If previousRange.Exists(cell.Address) Then
If previousRange.Item(cell.Address) <> cell.FormulaR1C1 Then
cell.Interior.ColorIndex = 36
End If
End If
Next
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim cell As Variant
Set previousRange = Nothing 'not really needed but I like to kill off old references
Set previousRange = CreateObject("Scripting.Dictionary")
For Each cell In Target.Cells
previousRange.Add cell.Address, cell.FormulaR1C1
Next
End Sub
ps. any vba code to update cells (even just colour) will stop excel's undo functionality from working! To get around this you can reprogram undo functionality, but it can get quite memory intensive. Sample solutions: http://www.jkp-ads.com/Articles/UndoWithVBA00.asp / http://www.j-walk.com/ss/excel/tips/tip23.htm

Answer 4

I know this is an old thread, but I had exactly the same problem like this "Change cell A1 and the cell gets highlighted. That's what I'd expect. Double click B1 but don't change the value there and then click C1. You'll notice B1 gets highlighted! "
I didn't wanted to highlight a cell if it was only doubleclicked without value inside.
I solved in in easy way. Maybe it help somebody in future.
I've just added this on the beggining of the event:
If Target.Value = "" Then
Exit Sub
End If

Answer 5

I found this other thread that provides ways to captures the old value, so you can compare it with the "new" value and if those are then simply let it do nothing.
How do I get the old value of a changed cell in Excel VBA?