Windows Form -----内容（5）

同一表格下的三级联动：

代码：

class DBconnection
    {
        public const string CONNECTIONSTRING = "server=.;database=mydb;uid=sa;pwd=5587725";
    }

class chinastates
    {
        public string AreaCode { get; set; }
        public string AreaName {get;set;}
        public string ParentAreaCode { get; set; }
    }

class chianstatesDA
    {
        private SqlConnection _Conn;
        private SqlCommand _Cmd;
        private SqlDataReader _DR;
        public chianstatesDA()
        {
            _Conn = new SqlConnection(DBconnection.CONNECTIONSTRING);
            _Cmd = _Conn.CreateCommand();
        }
        public List<chinastates> Select(string parentareacode)
        {
            List<chinastates> list = new List<chinastates>();
            _Cmd.CommandText = "select * from chinastates where [email protected]";
            _Cmd.Parameters.Clear();
            _Cmd.Parameters.AddWithValue("@parentareacode",parentareacode);
            try
            {
                _Conn.Open();
                _DR = _Cmd.ExecuteReader();
                while (_DR.Read())
                {
                    chinastates data = new chinastates();
                    data.AreaCode = _DR["AreaCode"].ToString();
                    data.AreaName = _DR["AreaName"].ToString();
                    data.ParentAreaCode = _DR["ParentAreaCode"].ToString();
                    list.Add(data);
                }
            }
            finally
            {
                _Conn.Close();
            }
            return list;
        }

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Fillprov()
        {
            //取数据
            List<chinastates> list = new chianstatesDA().Select("0001");
            //填进去
            cmbProv.DataSource = list;
            cmbProv.DisplayMember = "AreaName";
            cmbProv.ValueMember = "AreaCode";
        }
        private void Fillcity()
        {
            string prt = (cmbProv.SelectedItem as chinastates).AreaCode;
            List<chinastates> list = new chianstatesDA().Select(prt);
            cmbCity.DataSource = list;
            cmbCity.DisplayMember = "AreaName";
            cmbCity.ValueMember = "AreaCode";
        }
        private void Fillcounty()
        {
            string prt = "";
            if (cmbCity.SelectedItem!=null)
            {
                prt = (cmbCity.SelectedItem as chinastates).AreaCode;
            }
            List<chinastates> list = new chianstatesDA().Select(prt);
            cmbCounty.DataSource = list;
            cmbCounty.DisplayMember = "AreaName";
            cmbCounty.ValueMember = "AreaCode";
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Fillprov();
            Fillcity();
            Fillcounty();
        }

private void cmbProv_SelectedIndexChanged(object sender, EventArgs e)
        {
            Fillcity();
            Fillcounty();
        }

private void cmbCity_SelectedIndexChanged(object sender, EventArgs e)
        {
            Fillcounty();
        }
    }