无法转换类型的对象

Question

i want to get the maximum number

so i did this code

 public int autoIncrement()
    {
        int no = 0;
        odbcCon.OpenCon();
        SqlCommand cmd = new SqlCommand("SELECT MAX (CustomerCode) FROM TBLM_CUSTOMER",odbcCon.MainCon);

        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.Read())
        {
            if (!dr.IsDBNull(0)) {

                 no = Convert.ToInt32(dr);

            }

        }
        dr.Close();
        return no;

    }

but

no = Convert.ToInt32(dr);

says

Unable to cast object of type 'System.Data.SqlClient.SqlDataReader' to type 'System.IConvertible'.

how can i solve this ? please tell me

Answer 1

You're trying to convert your data reader to an integer.

Try this instead:

if (!dr.IsDBNull(0)) {
    no = dr.GetInt32(0);
}

Answer 2

您需要为DataReader指定索引0 ：

no = Convert.ToInt32(dr[0]);

Answer 3

你需要给索引：

no = Convert.ToInt32(dr[0]);

Answer 4

尝试获取GetSqlInt32属性

no = dr.GetSqlInt32(0);