VBA keep track of which workbooks are open - vba

Question

How can VBA keep track of which workbooks are open?
I am writing a data mining macro that takes information from a variable number of workbooks. The user may choose what workbooks will be parsed via a userform. However, workbooks can be opened and closed while the userform is running.
So, how can my userform keep track of which workbooks are open, so that it can display them accurately.
Right now, I'm using a recursive function that calls itself with "Application.OnTime". I don't really like this solution for because it involves extra checks to see if the userform is still open, as well as having a delay because of whatever period the function is called at.
Final: Combined solution from answers and comments
userform code, requires a ListBox called WorkbookList, and a Textbox called FileTextBox
Private WithEvents App As Application
Public Sub WorkbookList_UpdateList()
WorkbookList.Clear
For Each Wb In Application.Workbooks
WorkbookList.AddItem Wb.name
Next Wb
End Sub
Private Sub WorkbookList_Change()
If WorkbookList.ListIndex = -1 Then Exit Sub
key = WorkbookList.List(WorkbookList.ListIndex)
For Each Wb In Application.Workbooks
IsWorkBookOpen Wb.path
If Wb.name = key Then FileTextbox.text = Wb.path
Next Wb
End Sub
Private Sub App_WorkbookOpen(ByVal Wb As Workbook)
WorkbookList_UpdateList
End Sub
Private Sub App_NewWorkbook(ByVal Wb As Workbook)
WorkbookList_UpdateList
End Sub
Private Sub App_WorkbookBeforeClose(ByVal Wb As Workbook, Cancel As Boolean)
Application.OnTime Now + TimeValue("00:00:01"), "WorkbookClosed"
End Sub
Private Sub UserForm_Initialize()
Set App = Application
WorkbookList_UpdateList
UpdatePeriodicly
End Sub
module code (put this in a vba module):
'Code From: http://www.ozgrid.com/forum/showthread.php?t=152892
Function IsUserFormLoaded(ByVal UFName As String) As Boolean
Dim UForm As Object
IsUserFormLoaded = False
For Each UForm In VBA.UserForms
If UForm.name = UFName Then
IsUserFormLoaded = True
Exit For
End If
Next
End Function
Public Sub WorkbookClosed()
If IsUserFormLoaded("InputForm") = False Then Exit Sub
InputForm.WorkbookList_UpdateList
End Sub

Answer 1

You can use Application Events fgor this.
E.g. see cpearson.com/excel/appevent.aspx
Private WithEvents app As Excel.Application
Sub Init()
Set app = Application 'start capturing events
End Sub
Private Sub app_NewWorkbook(ByVal Wb As Workbook)
Debug.Print "New"
End Sub
Private Sub app_WorkbookBeforeClose(ByVal Wb As Workbook, Cancel As Boolean)
Debug.Print "Before close: " & Wb.Name
End Sub
Private Sub app_WorkbookOpen(ByVal Wb As Workbook)
Debug.Print "Open: " & Wb.Name
End Sub

Answer 2

So I think that this is an interesting script and something that might be useful for the problem your trying to solve.
Public Function IsWorkBookOpen(FileName As String)
Dim ff As Long, ErrNo As Long
On Error Resume Next
ff = FreeFile()
Open FileName For Input Lock Read As #ff
Close ff
ErrNo = Err
On Error GoTo 0
Select Case ErrNo
Case 0: IsWorkBookOpen = False 'Workbook IS NOT
Case 70: IsWorkBookOpen = True 'Workbook IS open
Case Else: Error ErrNo
End Select
End Function
You can call this by doing something like this
Ret = IsWorkBookOpen("C:\test.xlsm")
If Ret = True Then 'YOUR CODE HERE