Responding to directory events

[edellavedova]

What is the most resource efficient method of a VB application responding to a new file being written to a directory (other than creating an NT service)?

Thanks

[kedaman]

If you're not afraid of timers, I have a simple solution,.

[Aaron Young]

You can use the FindFirstChangeNotification API, ie.

Private Declare Function FindFirstChangeNotification Lib "kernel32" Alias "FindFirstChangeNotificationA" (ByVal lpPathName As String, ByVal bWatchSubtree As Long, ByVal dwNotifyFilter As Long) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long

Private Const FILE_NOTIFY_CHANGE_FILE_NAME = &H1

Private Sub Form_Activate()
    Dim lWait As Long
    
    lWait = 1
    While lWait
        lWait = FindFirstChangeNotification("C:\Files", True, FILE_NOTIFY_CHANGE_FILE_NAME)
        DoEvents
        If WaitForSingleObject(lWait, 100) = 0 Then
            Text1.SelText = "Something Changed." & vbCrLf
        End If
    Wend
End Sub

[Edited by Aaron Young on 04-03-2000 at 02:53 PM]

[kedaman]

This will return all new files in a variant containing an array:

Function SearchDIR(directory)
    
    On Error Resume Next 'oldfiles will cause subscript out of range the first time.
    Static oldfiles() As String 'This static remains in memory after first function call
    Dim newfiles() As String: ReDim newfiles(0) 'Temporary holds the new ones
    Dim foundfiles() As String: ReDim foundfiles(0) 'The array to send in return
    
    fil = Dir(directory, 7) 'Catch first file (hidden/system/archive files readen)
    Do Until fil = ""
        ReDim Preserve newfiles(UBound(newfiles) + 1) 'Resize array
        newfiles(UBound(newfiles) - 1) = fil
        For n = 0 To UBound(oldfiles) 'Search the old ones...
            If fil = oldfiles(n) Then ' ... to test if fil is old
                Exit For
            End If
            If n = UBound(oldfiles) Then '... if no matches, add to foundlist
                ReDim Preserve foundfiles(UBound(foundfiles) + 1) 'Resize array
                foundfiles(UBound(foundfiles) - 1) = fil 'Add
            End If
        Next n
        fil = Dir() 'Find next file
    Loop
    
    ReDim oldfiles(UBound(newfiles) - 1) 'Removing last empty item in each array
    ReDim Preserve newfiles(UBound(newfiles) - 1)
    ReDim Preserve foundfiles(UBound(foundfiles) - 1)
    For n = 0 To UBound(newfiles) ' Store filenames until next search
        oldfiles(n) = newfiles(n)
    Next n
    SearchDIR = foundfiles() 'Return the found files in array

End Function

Calling this function the first time wont return anything. Calling it next time will return all new files that are added since then. Hope you get things work!