Winform Commobox的数据源绑定

        调换下赋值的顺序就会报错！

        private DataSet ds = new DataSet();
        private void getProvinceAndCity()
        {
            GetPriceInfo_BLL bll = new GetPriceInfo_BLL();
            ds = bll.GetPriceInfoFromJsw_Bll();
            comPriceInfoProvince.DisplayMember = "province_name";
            comPriceInfoProvince.ValueMember = "province_id";
            comPriceInfoProvince.DataSource = ds.Tables["Province"];
            comPriceInfoProvince.SelectedIndex = 0;
        }

        //Get city according by province.
        private void comPriceInfoProvince_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comPriceInfoCity.Items.Count > 0)
            {
                comPriceInfoCity.DataSource = new DataTable();
            }
            int province_id = int.Parse(comPriceInfoProvince.SelectedValue.ToString());
            GetPriceInfo_BLL bll = new GetPriceInfo_BLL();
            DataTable dtOfCitys = bll.GetCitysByProvinceFromJsw_Dal(province_id);
            comPriceInfoCity.DataSource = dtOfCitys;
            comPriceInfoCity.DisplayMember = "city_name";
            comPriceInfoCity.ValueMember = "city_id";
            comPriceInfoCity.SelectedIndex = 0;
        }