省市两级联动combobox，如何进一步的完善？

Question

请教各位达人高手：
目前在做省市联动的代码中，出现情况combobox1,后combobox2的值无法第一时间改变。。整个代码如下：（数据库是access2007）
private void frmShowTel_Load(object sender, EventArgs e)
        {
            // 创建数据库连接
            using (OleDbConnection objConn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;
                                                    Data Source=../../database/Assist.accdb"))
            {
                objConn.Open();                    // 创建数据库的sql命令
                using (OleDbCommand objCmd = objConn.CreateCommand())
                {
                    objCmd.CommandText = "select distinct state from Domination";
                    using (OleDbDataReader objReader = objCmd.ExecuteReader())
                    {
                        while (objReader.Read())
                        {
                            string stateName = objReader.GetString(objReader.GetOrdinal("state"));
                            cmbState.Items.Add(stateName);
                        }
                    }
                }
            }        }        private void cmbState_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (this.cmbState.SelectedIndex !=0)
            {
                // 清空cmbCity的内容
                cmbCity.Items.Clear();                // 创建数据库连接
                using (OleDbConnection objConn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;
                                                    Data Source=../../database/Assist.accdb"))
                {                    objConn.Open();
                    // 创建数据库的sql命令，和第一个相同
                    using (OleDbCommand objCmd = objConn.CreateCommand())
                    {
                        objCmd.CommandText = "select city from Domination where state=cmbState.SelectedItem";
                        objCmd.Parameters.Add(new OleDbParameter("city", cmbState.SelectedItem));
                        using (OleDbDataReader objReader = objCmd.ExecuteReader())
                        {
                            while (objReader.Read())
                            {
                                string cityName = objReader.GetString(objReader.GetOrdinal("city"));
                                cmbCity.Items.Add(cityName);
                            }
                        }
                    }
                    objConn.Close();
                    objConn.Dispose();
                }
            }        }
ComboBox数据库

Answer 1

cmbState_SelectedIndexChanged有没有被执行，下一个断点调试下。