Éxcel-VBA Open Workbook in macro that have been called in a cell - vba

Question

I have some trouble with a function that I call from a cell in Excel.
The macro shall open a workbook get some data and then return a mathematical results to the cell.
But when I use the the following code it does not open the wordbook, just return #VALUE! to the cell. It break out of the code right after I tried to open the workbook.
' This Interpolation function is used to get data from other Excel sheets
Public Function DatasheetLookup(ExcelFile As String, ExcelSheet As String, xVal As Double, Optional isSorted As Boolean = True) As Variant
' abosolute or relative path?
If Not (Left(ExcelFile, 3) Like "[A-Z]:\") Or (Left(ExcelFile, 2) = "\\") Then
ExcelFile = ThisWorkbook.path & "\" & ExcelFile
End If
' does file exits?
If Dir(ExcelFile, vbDirectory) = vbNullString Then
DatasheetLookup = "No such file!"
Exit Function
End If
' open the source workbook, read only
Dim Wbk As Workbook
Dim WS As Worksheet
' Application.ScreenUpdating = False ' turn off the screen updating
Set Wbk = Workbooks.Open(ExcelFile)
' Run through all sheets in the source workBook to find "the one"
For Each WS In Wbk.Worksheets ' <-- Here it exit the code and return #VALUE!
If WS.Name <> ExcelSheet Then
DatasheetLookup = "Sheet not found!"
Else
Dim xRange As Range
Dim yRange As Range
xRange = WS.Range("A1", "A" & WS.UsedRange.Rows.Count)
yRange = WS.Range("B1", "B" & WS.UsedRange.Rows.Count)
Dim yVal As Double
Dim xBelow As Double, xAbove As Double
Dim yBelow As Double, yAbove As Double
Dim testVal As Double
Dim High As Long, Med As Long, Low As Long
Low = 1
High = WS.UsedRange.Rows.Count
If isSorted Then
' binary search sorted range
Do
Med = Int((Low + High) \ 2)
If (xRange.Cells(Med).Value) < (xVal) Then
Low = Med
Else
High = Med
End If
Loop Until Abs(High - Low) <= 1
Else
' search every entry
xBelow = -1E+205
xAbove = 1E+205
For Med = 1 To xRange.Cells.Count
testVal = xRange.Cells(Med)
If testVal < xVal Then
If Abs(xVal - testVal) < Abs(xVal - xBelow) Then
Low = Med
xBelow = testVal
End If
Else
If Abs(xVal - testVal) < Abs(xVal - xAbove) Then
High = Med
xAbove = testVal
End If
End If
Next Med
End If
xBelow = xRange.Cells(Low): xAbove = xRange.Cells(High)
yBelow = yRange.Cells(Low): yAbove = yRange.Cells(High)
DatasheetLookup = yBelow + (xVal - xBelow) * (yAbove - yBelow) / (xAbove - xBelow)
Exit For
End If
Next WS
Wbk.Close Savechanges:=False
Set Wbk = Nothing
Application.ScreenUpdating = True
End Function

Answer 1

I am not sure the reason for this specifically, but you cannot open a file in a user defined function. There are many additional actions that cannot be performed in a Function as well. This is also discussed in this Stack Overflow answer here.
However, in your case, you can easily cheat this limitation by opening the file you want to read before you call the function. I prepared a very basic demonstration of this, you will need to modify the code as needed to fit your particular example:
Code in "ThisWorkbook":
' when the workbook opens, also open the companion spreadsheet so it is available to use
Private Sub Workbook_Open()
Set Wbk = Workbooks.Open("C:\Users\lrr\Desktop\Myworkbook.xlsx")
End Sub
Code in "Module1":
Global Wbk As Workbook
Public Function testFunc()
' the workbook is already opened, so you may perform this iteration operation w/o any problems.
For Each WS In Wbk.Worksheets
testFunc = 1
Exit Function
Next WS
End Function
Code in Cell A1:
=testFunc()