winform/timer控件/权限设置/三级联动

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            //调查询方法
            Bind("0001", comboBox1);
            Bind(comboBox1.SelectedValue.ToString(), comboBox2);
            Bind(comboBox2.SelectedValue.ToString(), comboBox3);

        }

        public void Bind(string pcode, ComboBox cb)
        {
            //绑定数据
            List<China> clist = new ChinaData().Select(pcode);

            cb.DataSource = clist;
            cb.DisplayMember = "AreaName";
            cb.ValueMember = "AreaCode";
        }
        //二级下拉菜单条件判断
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            Bind(comboBox1.SelectedValue.ToString(), comboBox2);
            if (comboBox2.SelectedValue != null)
            {
                Bind(comboBox2.SelectedValue.ToString(), comboBox3);
            }
        }
        //三级体检判断
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            Bind(comboBox2.SelectedValue.ToString(), comboBox3);
        }