省市联动

--首先添加SQL类型，写应用程序配置文件，并分别引用

model

namespace 省市联动专属Helper版
{
    class model
    {
        public int ID
        {
            get;
            set;
        }
        public string Name
        {
            get;
            set;
        }
       -- //重写ToString
        public override string ToString()
        {
            return Name;
        }
    }
}

--专属Helper

 static class PCHelper
    {
        public static List<model> PCExcute(string commandText, params object[] objs)
        {
            List<model> list = new List<model>();
            using (SqlDataReader reader = SQLHelper.Class1.ExcuteReader(commandText, objs))
            {
                if (reader.HasRows)
                {
                    while (reader.Read())
                    {
                        list.Add(
                        new model {
                            ID=Convert.ToInt32(reader["AreaId"]),
                            Name=reader["AreaName"].ToString()
                        }
                        );
                    }
                }
            }
            return list;
        }
    }

--窗口

namespace 省市联动专属Helper版
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            string str = @"select AreaId,AreaName from TblArea where AreaPId=@p";
            cmdpro.Items.AddRange(PCHelper.PCExcute(str,0).ToArray());
        }

        private void cmdpro_SelectedIndexChanged(object sender, EventArgs e)
        {
            cmbcity.Items.Clear();
            cmbcity.Text = string.Empty;
            string str = @"select AreaId,AreaName from TblArea where AreaPId=@pid";
            int id = ((model)(cmdpro.SelectedItem)).ID;
            cmbcity.Items.AddRange(PCHelper.PCExcute(str, id).ToArray());
        }
    }
}

--Model类