当选择ComboBox的值时其他控件也跟着变化。
窗体控件：comboBox1，comboBox2，listBox1，textBox1
数据库表字段：ID Name ParentID

 private void Form1_Load(object sender, EventArgs e)
        {  DataBindComboBox();
   
        }
  public void DataBindComboBox()
        {
            BindingSource bindingSource = new BindingSource();
            bindingSource.DataSource = myDB.DatabindComboBox(string.Empty).Tables[0];
            comboBox1.DataSource = bindingSource;          
            comboBox1.DisplayMember = "Name";           
            
        }

/// <summary>
        /// 根据选择的省份获取省份的市
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {            
            string Condition = string.Format(" where ParentID in(select ID from DeptTree where Name='{0}')", comboBox1.Text);
             DataTable  dataTable=myDB.DatabindComboBox(Condition).Tables[0];
             if (dataTable.Rows.Count > 0)
             {
                 comboBox2.DataSource = dataTable;
                 comboBox2.DisplayMember = "Name";
                 listBox1.DataSource = dataTable;
                 listBox1.DisplayMember = "Name";
                
             }
             else
             {
                 comboBox2.DataSource = null;
                 listBox1.DataSource = null;
             }

           
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            textBox1.Text = listBox1.Text.ToString();
        }

   /// <summary>
        /// 把地名显示到控件中
        /// </summary>
        /// <returns></returns>
        public DataSet DatabindComboBox(string Condition)
        {
            string sqlstr = "select Name from DeptTree" + Condition;
            return RunSQL_DataTable(sqlstr);
        }