ListView: How to sort numbers?

[AlvaroF1]

The following code is working fine, but when it's storing numbers...

Friend Class Form1
    Inherits System.Windows.Forms.Form
    Private Sub ListView1_ColumnClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.ColumnClickEventArgs) Handles ListView1.ColumnClick
        If e.Column <> sortColumn Then
            sortColumn = e.Column
            ListView1.Sorting = SortOrder.Ascending
        Else
            If ListView1.Sorting = SortOrder.Ascending Then
                ListView1.Sorting = SortOrder.Descending
            Else
                ListView1.Sorting = SortOrder.Ascending
            End If
        End If
        ListView1.Sort()
        ListView1.ListViewItemSorter = New Comparer(e.Column, ListView1.Sorting)
    End Sub
End Class
Friend Class Comparer
    Implements IComparer
    Private Col As Integer
    Private Order As SortOrder
    Public Sub New()
        Col = 0
        Order = SortOrder.Ascending
    End Sub
    Public Sub New(ByVal column As Integer, ByVal order As SortOrder)
        Col = column
        Me.Order = order
    End Sub
    Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer Implements System.Collections.IComparer.Compare
        Dim returnVal As Integer = -1
        returnVal = String.Compare(CType(x, ListViewItem).SubItems(Col).Text, CType(y, ListViewItem).SubItems(Col).Text)
        If Order = SortOrder.Descending Then returnVal *= -1
        Return returnVal
    End Function
End Class

For example it returns:

1
10
2
20

Instead of:

1
2
10
20


How to fix it?

Thanks.