dropdownlist级联问题

Question

  protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            bindtoChannel();
            bindtoClass();
        }
    }
    protected void bindtoChannel()//绑定频道列表
    {
        DataTable dt = db.GetList("select * from Common_Channel");
        this.ddl_channel.DataSource = dt.DefaultView;
        this.ddl_channel.DataTextField = "C_Name";
        this.ddl_channel.DataValueField = "C_Code";
        this.ddl_channel.DataBind();
    }
    protected void bindtoClass()//绑定到板块列表
    {
        string strwhere = "select * from Common_Class where C_Code='" + this.ddl_channel.SelectedValue + "'";
       // string strwhere = "select * from  Common_Class";
        DataTable dt1 = db.GetList(strwhere);
        this.ddl_calss.DataSource = dt1.DefaultView;
        this.ddl_calss.DataTextField = "CLS_Name";
        this.ddl_calss.DataValueField = "CLS_ID";
        this.ddl_calss.DataBind();
    }
    protected void ddl_channel_SelectedIndexChanged(object sender, EventArgs e)
    {
       string c_code = this.ddl_channel.SelectedValue.ToString();
        string strwhere = "select * from Common_Class where C_Code='" + c_code + "'";
        DataTable dt1 = db.GetList(strwhere);
        this.ddl_calss.DataSource = dt1.DefaultView;
        this.ddl_calss.DataTextField = "CLS_Name";
        this.ddl_calss.DataValueField = "CLS_ID";
        this.ddl_calss.DataBind();
    }频道的下拉框可以绑定数据 但是板块的下拉框没有  也不能实现级联 各位帮帮忙 看看哪有问题  
我实在是没找到啊 谢谢了 各位！

Answer 1

protected void Page_Load(object sender, EventArgs e)
  {
  if (!IsPostBack)
  {
  bindtoChannel();
  }
  }
  protected void bindtoChannel()//绑定频道列表
  {
  DataTable dt = db.GetList("select * from Common_Channel");
  this.ddl_channel.DataSource = dt.DefaultView;
  this.ddl_channel.DataTextField = "C_Name";
  this.ddl_channel.DataValueField = "C_Code";
  this.ddl_channel.DataBind();
  }
  protected void bindtoClass()//绑定到板块列表
  {
  string strwhere = "select * from Common_Class where C_Code='" + this.ddl_channel.SelectedValue + "'";
  // string strwhere = "select * from Common_Class";
  DataTable dt1 = db.GetList(strwhere);
  this.ddl_calss.DataSource = dt1.DefaultView;
  this.ddl_calss.DataTextField = "CLS_Name";
  this.ddl_calss.DataValueField = "CLS_ID";
  this.ddl_calss.DataBind();
  }
  protected void ddl_channel_SelectedIndexChanged(object sender, EventArgs e)
  {
  bindtoClass();
  string c_code = this.ddl_channel.SelectedValue.ToString();
  string strwhere = "select * from Common_Class where C_Code='" + c_code + "'";
  DataTable dt1 = db.GetList(strwhere);
  this.ddl_calss.DataSource = dt1.DefaultView;
  this.ddl_calss.DataTextField = "CLS_Name";
  this.ddl_calss.DataValueField = "CLS_ID";
  this.ddl_calss.DataBind();
  }

Answer 2

if (!IsPostBack)
  {
  bindtoChannel();
  }