How do I find out why I get an error when writing to an Excel cell with VBA? - vba

Question

I'm still fairly new to VBA and struggling with its limitations (and mine!). Here's my code:
Sub updateCache(CacheKey As String, CacheValue As Variant)
Dim DataCacheWorksheet As Worksheet, CacheRange As Range, Found As Variant, RowNum As Integer
Set DataCacheWorksheet = ThisWorkbook.Worksheets("DataCache")
Set CacheRange = DataCacheWorksheet.Range("A1:B999")
Set Found = CacheRange.Find(What:=CacheKey)
If Found Is Nothing Then
RowNum = CacheRange.Cells(Rows.Count, 2).End(xlUp).Row
DataCache.Add CacheKey, CacheValue
On Error Resume Next
DataCacheWorksheet.Cells(1, 1).Value = CacheKey
DataCacheWorksheet.Cells(1, 2).Value = CacheValue
Else
'Do other things
End If
End Sub
When I step through the code, Excel simply exits the sub at the line DataCacheWorksheet.Cells(1, 1).Value = CacheKey, with no error. So, two questions:
What's the bug that's preventing the value from being updated?
Why does Excel ignore my On Error command?
Edit: If I run the line in the IDE's "Immediate" box, I get the error "Run-time error '1004' Application-defined or object-defined error. I get the same error regardless of the value of CacheKey (I tried Empty, 1234 and "Hello").
Edit 2: If I modify the sub so that CacheKey and CacheValue are hardcoded and the reference to DataCache is removed, and then I run the sub standalone it works. So why doesn't it work when called from another function? Is it possible that Excel is locking cells while doing calculations?

Answer 1

Not sure if this applies, but you mentioned you were calling this macro from another function. If you are calling it from a function, depending on how you are calling it, that would explain your problem. For example, a worksheet function entered into a cell cannot modify another cell on the worksheet. And the attempt to do so will result in the macro merely exiting at that point, without throwing a VBA error.
How to work around this depends on specifics you have yet to share. Sometimes, worksheet event code can be useful.

Answer 2

Ok, wasn't about to write an answer, but there are 3 things you should modify in your code:
Found As Range and not As Variant
RowNum As Long in case it's a row after ~32K
To trap errors usually On Error Resume Next won't help you, it will just jump one line of code. You need to handle the error situation.
Modified Code
Sub updateCache(CacheKey As String, CacheValue As Variant)
Dim DataCacheWorksheet As Worksheet, CacheRange As Range, Found As Range, RowNum As Long ' < use Long instead of Integer
Set DataCacheWorksheet = ThisWorkbook.Worksheets("DataCache")
Set CacheRange = DataCacheWorksheet.Range("A1:B999")
Set Found = CacheRange.Find(What:=CacheKey)
If Found Is Nothing Then ' check if not found in cache (*Edit 1)
RowNum = CacheRange.Cells(Rows.Count, 2).End(xlUp).Row
DataCache.Add CacheKey, CacheValue ' I assume you have a `Dictionary somewhere
' On Error Resume Next <-- Remove this, not recommended to use
DataCacheWorksheet.Cells(1, 1).Value = CacheKey
DataCacheWorksheet.Cells(1, 2).Value = CacheValue
Else
'Do other things
End If
End Sub