protected void DropDownListMark_SelectedIndexChanged(object sender, EventArgs e)
    {
        bool status = false;
        foreach (GridViewRow row in GridViewMessageBox.Rows)
        {
            CheckBox checkBox = (CheckBox)row.Cells[0].FindControl("CheckBoxMessage");
            if (checkBox.Checked)
            {
                HiddenField hiddenField = (HiddenField)row.Cells[0].FindControl("HiddenFieldMessage");
                string messageUserOID = hiddenField.Value;
                MessageCenter messageCenter = new MessageCenter();
                if ((DropDownListMark.SelectedItem.Text == "Mark") || (DropDownListMark.SelectedItem.Text == "Star"))
                {
                    if (messageCenter.UpdateMessageUserUMark(Convert.ToInt32(messageUserOID), 1))
                        status = true;
                }
                else
                {
                    if (messageCenter.UpdateMessageUserUStatus(Convert.ToInt32(messageUserOID), DropDownListMark.SelectedItem.Text))
                        status = true;
                }

            }
        }
        if (status)
        {
            PopulateMessageBox();
        }
    }