DataGridViewのコンボボックスを変更不可にする方法

DataGridViewのコンボボックスを変更不可にする方法
VB.NET

Private Sub dgv1_EditingControlShowing(ByVal sender As Object, _
        ByVal e As DataGridViewEditingControlShowingEventArgs) _
        Handles dgv1.EditingControlShowing
    If TypeOf e.Control Is DataGridViewComboBoxEditingControl Then
        Dim dgv As DataGridView = CType(sender, DataGridView)
        If dgv.CurrentCell.OwningColumn.Name = "ComboBox" Then
            Dim cb As DataGridViewComboBoxEditingControl = _
                CType(e.Control, DataGridViewComboBoxEditingControl)
            cb.DropDownStyle = ComboBoxStyle.DropDown
        End If
    End If
End Sub

Private Sub dgv1_CellValidating(ByVal sender As Object, _
        ByVal e As DataGridViewCellValidatingEventArgs) _
        Handles dgv1.CellValidating
    Dim dgv As DataGridView = CType(sender, DataGridView)
    If dgv.Columns(e.ColumnIndex).Name = "ComboBox" AndAlso _
        TypeOf dgv.Columns(e.ColumnIndex) Is DataGridViewComboBoxColumn Then
        Dim cbc As DataGridViewComboBoxColumn = _
            CType(dgv.Columns(e.ColumnIndex), DataGridViewComboBoxColumn)
        If Not cbc.Items.Contains(e.FormattedValue) Then
            cbc.Items.Add(e.FormattedValue)
        End If
        dgv(e.ColumnIndex, e.RowIndex).Value = e.FormattedValue
    End If
End Sub

C#

private void dgv1_EditingControlShowing(object sender,
    DataGridViewEditingControlShowingEventArgs e)
{
    if (e.Control is DataGridViewComboBoxEditingControl)
    {
        DataGridView dgv = (DataGridView)sender;
        if (dgv.CurrentCell.OwningColumn.Name == "ComboBox")
        {
            DataGridViewComboBoxEditingControl cb =
                (DataGridViewComboBoxEditingControl)e.Control;
            cb.DropDownStyle = ComboBoxStyle.DropDown;
        }
    }
}

private void dgv1_CellValidating(object sender,
    DataGridViewCellValidatingEventArgs e)
{
    DataGridView dgv = (DataGridView)sender;
    if (dgv.Columns[e.ColumnIndex].Name == "ComboBox" &&
        dgv.Columns[e.ColumnIndex] is DataGridViewComboBoxColumn)
    {
        DataGridViewComboBoxColumn cbc =
            (DataGridViewComboBoxColumn)dgv.Columns[e.ColumnIndex];
        if (!cbc.Items.Contains(e.FormattedValue))
        {
            cbc.Items.Add(e.FormattedValue);
        }
        dgv[e.ColumnIndex, e.RowIndex].Value = e.FormattedValue;
    }
}