hsggetdata()函数获取session时，出现未将对象引用到实例

if (!IsPostBack)
{
//string strsql;
//strsql = "select * from List order by id desc";
//strsql = " select * from List where Title and Word like '%'and Word like'%" + TextBox1.Text + "%'";
// strsql="select * from BoWorkAfter,ConsultData,Download,employ,inform,InformationOpen,Organiaztion,Organiaztion,Organiaztion,ServiceGuide where Content like '%" + TextBox1.Text + "%'";
//ds = new Class1().hsggetdata(strsql);, "tbNews"

        DataSet ds = new DataSet();
        ds = new Class1().hsggetdata(Convert.ToString(Session["search"]));
        Repeater2.DataSource = ds.Tables[0];
        Repeater2.DataBind();
        Label1.Text = Convert.ToString(Session["tool"]);
    }

             public DataSet hsggetdata(string sql)  //自定义函数,查询数据库,将得到的数据以dataset型返回
{
    //myConnection.Open();

    //SqlConnection myConnection=new SqlConnection(ConfigurationSettings.AppSettings["strConn"]);

    SqlConnection conn = new SqlConnection();  //这几句都与上相同
    conn.ConnectionString = connstring;
    SqlCommand myCommand = new SqlCommand(sql, conn);

    SqlCommand cmd = new SqlCommand(sql, conn);

    try
    {
        // myConnection.Open();

        SqlDataAdapter da = new SqlDataAdapter(myCommand);  //定义一个新dataadapter,用于接收数据
        DataSet ds = new DataSet();  //定义新dataset用于接收数据
        da.Fill(ds);  //将da里的值赋给ds

        return ds;  //返回ds
    }
    catch
    {
        //Console.WriteLine("SqlException:{0}",SQLexc);
        return null;  //如果异常,返回null

    }
    finally
    {
        conn.Close();  //关闭数据库连接
    }
}