c#下拉列表联动

Question

那位大哥能给个c#中下拉列表联动的例子？

Answer 1

从数据库里读出数据放到下拉列表里：
 public void drop1()
    {
        if (!IsPostBack)
        {
            //连接数据库            //向下拉列表1增添数据
            SqlCommand cmd = new SqlCommand("SELECT DISTINCT yqkfdw FROM jcjlb where sp='审批人'", conn);
            SqlDataReader mydr = cmd.ExecuteReader();
            while (mydr.Read())
            {
                ListItem lt = new ListItem();
                lt.Text = mydr[0].ToString().Trim();
                lt.Value = mydr[0].ToString().Trim();
                this.DropDownList3.Items.Add(lt);
            }
            mydr.Close();
            string yqkf = DropDownList3.SelectedValue;
            conn.Close();            //执行drop2，向下拉列表2中填数据
            this.drop2();
        }
    }
public void drop2()
    {        //连接数据库，如果第一个下拉列表的值为“全部”：
            if (DropDownList3.Text == "全部")
            {
                DropDownList4.Items.Clear();
                ListItem lt4 = new ListItem();
                lt4.Text = "全部";
                this.DropDownList4.Items.Add(lt4);                SqlCommand cmd1 = new SqlCommand("SELECT DISTINCT sgdw FROM jcjlb where sp='审批人'", conn1);
                SqlDataReader dr1 = cmd1.ExecuteReader();
                while (dr1.Read())
                    {                        ListItem lt1 = new ListItem();
                        lt1.Text = dr1[0].ToString();
                        lt1.Value = dr1[0].ToString();
                        this.DropDownList4.Items.Add(lt1);
                    }                                        dr1.Close();
                    conn1.Close();
               
            }
            else
            {
                
                    DropDownList4.Items.Clear();
                    string sg = DropDownList3.Text.Trim();
                    SqlCommand cmd2 = new SqlCommand("SELECT DISTINCT sgdw FROM jcjlb where yqkfdw='" + sg + "'and sp='审批人'", conn1);
                    SqlDataReader dr2 = cmd2.ExecuteReader();
                    while (dr2.Read())
                    {                        ListItem lt2 = new ListItem();
                        lt2.Text = dr2[0].ToString().Trim();
                        lt2.Value = dr2[0].ToString().Trim();
                        this.DropDownList4.Items.Add(lt2);
                    }                    ListItem lt3 = new ListItem();
                    lt3.Text = "全部";
                    this.DropDownList4.Items.Add(lt3);                    dr2.Close();
                    conn1.Close();
                }
            
        
    } protected void DropDownList3_SelectedIndexChanged(object sender, EventArgs e)
    {
        this.drop2();
    }drop1放到page_load里面，dropdownlist3是第一个下拉菜单这是我从网上搜来自己改了一点无关紧要的东西，用的还可以，要是着急的话可以先这么用着，还有N多无刷新的也可以找找