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I'm making a WinForm project that shows me all the Excel files older than x months of a selected folder.

I can populate a ListBox with all the Excel files (see code below).

In selecting the older than x month, I don't succeed. I think I should work with the LastWriteTime but can’t find how to use it.

Can anyone help me to find a solution on this?

Private Sub ListFiles(ByVal folderPath As String)
 filesListBox.Items.Clear()

 Dim fileNames As String() =
 System.IO.Directory.GetFiles(folderPath,
 "*.xl*", System.IO.SearchOption.TopDirectoryOnly)

 For Each fileName As String In fileNames
 fileslistbox.Items.Add(fileName)
 Next
End Sub

The information on the a File Creation Time / Last Write Time is returned by the FileInfo class, which provides the Creation Time, Last Write Time and Last Access Time of a file through a FileSystemInfo class.

See whether you need the File Creation Time or the Last Write Time, depending on what your requirements are.

The Last Access Time may return just the file Creation DateTime, depending on the System.

An example, with a modified ListFiles method:

I've added a parameter to the method, OlderThanMonths, which is used to specify how old a file should be to be included in the list.

Here, the DateTime reference is LastWriteTime.

Private Sub ListFiles(ByVal folderPath As String, OlderThanMonths As Integer)
 filesListBox.Items.Clear()

 Dim fileNames As String() = Directory.GetFiles(folderPath, "*.xl*", SearchOption.TopDirectoryOnly)

 ListBox1.BeginUpdate()
 For Each fileName As String In fileNames
 Dim FIinfo As New FileInfo(fileName)
 If FIinfo.LastWriteTime.AddMonths(OlderThanMonths) <= Date.Now Then
 filesListBox.Items.Add(fileName)
 End If
 Next
 ListBox1.EndUpdate()
End Sub

Or with a LINQ Where() filter:

Private Sub ListFiles(ByVal folderPath As String, OlderThanMonths As Integer)
 filesListBox.Items.Clear()

 filesListBox.Items.AddRange(
 Directory.GetFiles(folderPath, "*.xl*", SearchOption.TopDirectoryOnly).
 Where(Function(f) New FileInfo(f).LastWriteTime.AddMonths(OlderThanMonths) <= Date.Now).
 ToArray())
End Sub

You are almost there. Just need to add an IF clause to check the Modified Date.

Check this code sample:

Private Sub ListFiles(ByVal folderPath As String)
 filesListBox.Items.Clear()

 Dim fileNames As String() =
 System.IO.Directory.GetFiles(folderPath,
 "*.xl*", System.IO.SearchOption.TopDirectoryOnly)

 For Each fileName As String In fileNames
 Dim dtFileModifiedDate As DateTime = IO.File.GetLastWriteTime(fileName)
 Dim dtCustomDate As DateTime = DateTime.ParseExact(20180401, "yyyyMMdd", Globalization.CultureInfo.InvariantCulture)
 If dtFileModifiedDate > dtCustomDate Then
 filesListBox.Items.Add(fileName)
 End If
 Next
End Sub