Filename is empty when trying to open file - vba

Question

I try to merge workbooks from a folder in a new workbooks. The VBA code reads the excel file from folder, add every file name to a list box and then, after pressing the button "Start", add very file to the workbook. That is the idea.
The code is as folows:
When opening the file the userform is shown:
Private Sub Workbook_Open()
UserForm1.Show
End Sub
When activating userform, the list box is populated:
Private Sub UserForm_Activate()
Const strFolder As String = "C:\Users\user\Desktop\tmp\"
Const strPattern As String = "*.xls"
Dim strFile As String
Dim collection As New collection
Dim i As Integer
Dim isMerger As Integer
Dim lngth As Integer
strFile = Dir(strFolder & strPattern, vbNormal)
If (StrComp(strFile, "FileMerger.xls") <> 0) Then
If (Len(strFile) <> 0) Then
col.Add (strFolder & strFile)
Do While Len(strFile) > 0
strFile = Dir
If (StrComp(strFile, "FileMerger.xls") <> 0) Then
If (Len(strFile) <> 0) Then
col.Add (strFolder & strFile)
End If
End If
Loop
End If
End If
Vars.xlsFiles = ColToArray(collection)
For i = 1 To UBound(Vars.xlsFiles)
lstFiles.AddItem (Vars.xlsFiles(i))
Next i
End Sub
At this moment listbox and array Vars.xlsFiles are populated; they are OK.
Click on Start button in the userform:
Private Sub cmdStart_Click()
Dim fileName As String
Dim sheet As Worksheet
Dim i As Integer
Dim ub As Integer
ub = UBound(Vars.xlsFiles)
For i = 1 To ub
Workbooks.Open fileName:=Vars.xlsFiles(i), ReadOnly:=True
For Each sheet In ActiveWorkbook.Sheets
sheet.Copy After:=ThisWorkbook.Sheets(1)
Next sheet
Workbooks(fileName).Close
Next i
End Sub
In the folder are 3 files. Their name are in the listbox. But when the first is to be closed I received an error message and after debugging it says that fileName ="" (line Workbooks(fileName).Close).
whatever I try I got the same error, i.e. fileName = "".
What to do ?

Answer 1

Your never set the variable fileName, so it's still the default value "". Maybe you got confused by the fileName:=Vars.xlsFiles(i) of the Workbooks.Open method. That just sets the option FileName of that method. Use some unique name to avoid confusion and set it to Vars.xlsFiles(i) or use
Workbooks(Vars.xlsFiles(i)).close

Answer 2

FileName:= is a named parameter of the Workbooks.Open method. It does not set the value of the cmdStart_Click's fileName variable.
Private Sub cmdStart_Click()
Dim fileName As String
Dim sheet As Worksheet
Dim i As Integer
Dim ub As Integer
ub = UBound(Vars.xlsFiles)
For i = 1 To ub
fileName = Vars.xlsFiles(i)
Workbooks.Open FileName:=fileName, ReadOnly:=True
For Each sheet In ActiveWorkbook.Sheets
sheet.Copy After:=ThisWorkbook.Sheets(1)
Next sheet
Workbooks(fileName).Close
Next i
End Sub