控件联动（三级联动）

关联数据库

public Form1()
        {
            InitializeComponent();

            //绑定省
            comboBox1.DataSource = new ChinaData().Select("0001");
            comboBox1.DisplayMember = "AreaName";
            comboBox1.ValueMember = "AreaCode";

            //绑定市
            comboBox2.DataSource = new ChinaData().Select(comboBox1.SelectedValue.ToString());
            comboBox2.DisplayMember = "AreaName";
            comboBox2.ValueMember = "AreaCode";

            //绑定区县
            comboBox3.DataSource = new ChinaData().Select(comboBox2.SelectedValue.ToString());
            comboBox3.DisplayMember = "AreaName";
            comboBox3.ValueMember = "AreaCode";

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            //绑定市
            comboBox2.DataSource = new ChinaData().Select(comboBox1.SelectedValue.ToString());
            comboBox2.DisplayMember = "AreaName";
            comboBox2.ValueMember = "AreaCode";
        }

        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            //绑定区县
            comboBox3.DataSource = new ChinaData().Select(comboBox2.SelectedValue.ToString());
            comboBox3.DisplayMember = "AreaName";
            comboBox3.ValueMember = "AreaCode";
        }