C#中comboBox实现三级联动

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;using System.Collections;namespace Select{ public partial class Form1 : Form { public Form1() {  InitializeComponent(); } Hashtable province = new Hashtable(); Hashtable city = new Hashtable(); private void Province() {  province.Add("云南省",new string[] {"昆明市","玉溪市" });  province.Add("四川省", new string[] { "成都市", "绵阳市" });  city.Add("昆明市",new string[] {"盘龙区","五华区" });  city.Add("玉溪市",new string[] {"红塔区","。。。区" });  city.Add("成都市", new string[] { "。。。区", "。。。区" });  city.Add("绵阳市", new string[] { "...区", "...区" }); } private void Form1_Load(object sender, EventArgs e) {  Province();  foreach (string str in province.Keys)  {  comboBox1.Items.Add(str);  }  foreach (string str in city.Keys)  {  comboBox2.Items.Add(str);  }  comboBox1.SelectedIndex=0; } private void comboBox1_SelectedIndexChanged(object sender, EventArgs e) {  string[] citys = province[comboBox1.Text] as string[];  comboBox2.Items.Clear();  foreach (string s in citys)  {  comboBox2.Items.Add(s);  }   comboBox2.SelectedIndex = 0; } private void comboBox2_SelectedIndexChanged(object sender, EventArgs e) {  string[] citys = city[comboBox2.Text] as string[];  comboBox3.Items.Clear();  foreach (string str in citys)  {  comboBox3.Items.Add(str);  }  comboBox3.SelectedIndex = 0; } private void comboBox3_SelectedIndexChanged(object sender, EventArgs e) { } }}