索引超出范围。必须为非负数且小于集合的大小。参数名称：使用Sqldatareader 取数据时的索引

Question

目前我在尝试使用 SqlDataReader 获取数据时遇到错误并且参数在列表中，即 newcmd.Parameters.Add("@frmcat", res[i]);

这是我的代码

        SqlDataAdapter adpt = new SqlDataAdapter("SELECT DISTINCT TOP 5 category, COUNT(category) AS totcom FROM coupon_deal WHERE (company LIKE '%" + query + "%') GROUP BY category ORDER BY totcom DESC", conn);
        DataTable dt = new DataTable();
        adpt.Fill(dt);

        int TotalRow = dt.Rows.Count;

        List<string> res = new List<string>();
        for (int i = 0; i < TotalRow; i++)
        {
            res.Add(dt.Rows[i]["category"].ToString());
        }

        List<string> cl = new List<string>();
        SqlCommand newcmd = new SqlCommand("SELECT company, count(company) AS totcomp from coupon_deal Where (category LIKE @frmcat) GROUP BY company ORDER BY totcomp DESC", conn);
        for (int i = 0; i <= res.Count; i++)
        {
            newcmd.Parameters.Clear();
            newcmd.Parameters.Add("@frmcat", res[i]);
            SqlDataReader sdr = newcmd.ExecuteReader();
            if (sdr.HasRows)
            {
                while (sdr.Read())
                {
                    cl.Add(sdr["company"].ToString());
                }
            }
            sdr.Close();
            sdr.Dispose();
        }

Answer 1

所以我 < res.Count 应该解决问题：

    for (int i = 0; i < res.Count; i++)
    {
        newcmd.Parameters.Clear();
        newcmd.Parameters.Add("@frmcat", res[i]);
        SqlDataReader sdr = newcmd.ExecuteReader();
        if (sdr.HasRows)
        {
            while (sdr.Read())
            {
                cl.Add(sdr["company"].ToString());
            }
        }
        sdr.Close();
        sdr.Dispose();
    }

索引超出范围。必须为非负数且小于集合的大小。参数名称：使用Sqldatareader 取数据时的索引

Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index while fetch data using Sqldatareader

c#

asp.net

for-loop

list

sqldatareader