大家多多共享啊

我想调用下面类中 Getdataset中的ds在窗体上用，但调不出来，谁帮我看看要怎么写啊


class DataAccess
    {
        public static string Connectionstring = "Data Source=.;Initial Catalog=CJGL;Integrated Security=true";
        public bool ExecuteSql(string sql)
        {
            SqlConnection con = new SqlConnection(DataAccess.Connectionstring);
            SqlCommand cmd = new SqlCommand(sql, con);
            try
            {
                con.Open();
                cmd.ExecuteNonQuery();
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                con.Close();
                con.Dispose();
                cmd.Dispose();
            }
        }
        public SqlDataReader Getreader(string sql)
        {
            SqlConnection con = new SqlConnection(DataAccess.Connectionstring);
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader dr = null;
            try
            {
                con.Open();
                dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch(Exception ex)
            {            
                dr.Close();//每次调用完DataReader对象后都要关闭的
                con.Dispose();
                cmd.Dispose();
                throw new Exception(ex.ToString());
            }
                return dr;
        }
        public  DataSet Getdataset(string sql, string tablename)
        {
            DataSet ds = new DataSet();
            SqlConnection con = new SqlConnection(DataAccess.Connectionstring);
            SqlDataAdapter da = new SqlDataAdapter(sql, con);
            try
            {
                da.Fill(ds, tablename);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }
            finally
            {
                con.Close();
                con.Dispose();
                da.Dispose();
            }
            return ds;
        }
        public int Getcount(string sql)
        {
            SqlConnection con = new SqlConnection(DataAccess.Connectionstring);
            SqlCommand cmd = new SqlCommand(sql, con);
            try
            {
                con.Open();
                int count = (int)cmd.ExecuteScalar();
                return count;
            }
            catch
            {
                return 0;
            }
            finally
            {
                con.Close();
                con.Dispose();
                cmd.Dispose();
            }
        }
        public  bool Checkadmin(string strname, string strpwd)
        {
            string sql;
            //strname =NameReplace(strname);
            sql = "select count(1) from UserInfo where Userid='"+strname+"'and Userpwd='" + strpwd + "'";
            if (Getcount(sql) > 0)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }