联动ddl

string strConn;
    string strSQL;
    SqlConnection sqlConn;
    int ID = 0;
    protected void Page_Load(object sender, EventArgs e)
    {
        strConn = System.Configuration.ConfigurationManager.AppSettings["ConnectString"];
        sqlConn = new SqlConnection(strConn);
        if (!IsPostBack)
        {
           
           
            this.BigClass();
            this.SmallClass(ID);
        }
       
      
       
    }
    protected void BigClass()
    {
       
       
        SqlCommand sqlComm = new SqlCommand();
        sqlComm.Connection = sqlConn;
        strSQL = "SELECT * FROM tBigClass";
        sqlComm.CommandText = strSQL;
        SqlDataAdapter sda = new SqlDataAdapter();
        sda.SelectCommand = sqlComm;
        DataSet ds = new DataSet();
        sqlComm.Connection.Open();
        sda.Fill(ds, "tBigClass");
        ddlBigClass.DataSource = ds.Tables["tBigClass"];
        ddlBigClass.DataTextField = "MBTitle";
        ddlBigClass.DataValueField = "ID";
        ddlBigClass.DataBind();
        ddlBigClass.Items.Insert(0, new ListItem("请选择--", ""));
        sqlComm.Connection.Close();

    }
    protected void SmallClass(int ID)
    {
       
       
        SqlCommand sqlComm = new SqlCommand();
        sqlComm.Connection = sqlConn;
        strSQL = "SELECT * FROM tSmallClass WHERE MSPid=@MSPid";
        sqlComm.CommandText = strSQL;
        sqlComm.Parameters.Add(new SqlParameter("@MSPid", SqlDbType.Int));
        sqlComm.Parameters["@MSPid"].Value = ID;
        SqlDataAdapter sda = new SqlDataAdapter();
        sda.SelectCommand = sqlComm;
        DataSet ds = new DataSet();
        sqlComm.Connection.Open();
        sda.Fill(ds, "tSmallClass");
        ddlSmallClass.DataSource = ds.Tables["tSmallClass"];
        ddlSmallClass.DataTextField = "MSTitle";
        ddlSmallClass.DataValueField = "ID";
        ddlSmallClass.DataBind();
        ddlSmallClass.Items.Insert(0, new ListItem("请选择--", ""));
        sqlComm.Connection.Close();
       

    }

    protected void btnSubmit_Click(object sender, EventArgs e)
    {

    }
    protected void ddlBigClass_SelectedIndexChanged(object sender, EventArgs e)
    {

        ID = Convert.ToInt32(ddlBigClass.SelectedValue);
        this.BigClass();
        ddlBigClass.SelectedValue = ID.ToString() ;
       
        this.SmallClass(ID);
       
      
    }