Private Sub SortButton_Click(ByVal sender As Object, _
    ByVal e As EventArgs) Handles sortButton.Click

    ' Check which column is selected, otherwise set NewColumn to Nothing.
    Dim newColumn As DataGridViewColumn
    If dataGridView1.Columns.GetColumnCount(DataGridViewElementStates _
        .Selected) = 1 Then
        newColumn = dataGridView1.SelectedColumns(0)
    Else
        newColumn = Nothing
    End If

    Dim oldColumn As DataGridViewColumn = dataGridView1.SortedColumn
    Dim direction As ListSortDirection

    ' If oldColumn is null, then the DataGridView is not currently sorted.
    If oldColumn IsNot Nothing Then

        ' Sort the same column again, reversing the SortOrder.
        If oldColumn Is newColumn AndAlso dataGridView1.SortOrder = _
            SortOrder.Ascending Then
            direction = ListSortDirection.Descending
        Else

            ' Sort a new column and remove the old SortGlyph.
            direction = ListSortDirection.Ascending
            oldColumn.HeaderCell.SortGlyphDirection = SortOrder.None
        End If
    Else
        direction = ListSortDirection.Ascending
    End If


    ' If no column has been selected, display an error dialog  box.
    If newColumn Is Nothing Then
        MessageBox.Show("Select a single column and try again.", _
            "Error: Invalid Selection", MessageBoxButtons.OK, _
            MessageBoxIcon.Error)
    Else
        dataGridView1.Sort(newColumn, direction)
        If direction = ListSortDirection.Ascending Then
            newColumn.HeaderCell.SortGlyphDirection = SortOrder.Ascending
        Else
            newColumn.HeaderCell.SortGlyphDirection = SortOrder.Descending
        End If
    End If

End Sub