为什么我的代码无法将值分配到文本框中.... [英] why my code does not working to assign value into a textbox....

问题描述

这些代码有什么问题请帮助

  string  conStr = ConfigurationManager.ConnectionStrings [  CStringCRM]。ToString（）; 
 DataTable dt =  new  DataTable（）; 
 SqlDataReader dr =  null ; 
 使用（SqlConnection conn =  new  SqlConnection（conStr））
 {
  string  sql =  string  .Format（ @ 选择前1个ID来自用户订单ID desc）; 
 SqlCommand cmd =  new  SqlCommand（）; 
 cmd.Connection = conn; 
 cmd.CommandText = sql; 
 cmd.CommandType = CommandType.Text; 
 conn.Open（）; 
 
 dr = cmd.ExecuteReader（）; 
 
 dt.Load（dr）; 
 txtUID.Text = dr [  ID]。ToString（）; 
 conn.Close（）; 
 cmd =  null ; 
 
} 

解决方案

以下是您的代码的固定版本：

< pre lang =cs> string conStr = ConfigurationManager.ConnectionStrings [ CStringCRM]的ToString（）;

使用（SqlConnection conn = new SqlConnection（conStr））
使用（SqlCommand cmd = new SqlCommand（ @ SELECT top 1 ID FROM用户订单ID desc，conn））
{
conn.Open（）;
使用（SqlDataReader dr = command.ExecuteReader（CommandBehavior.CloseConnection））
{
if （dr.Read（））
{
txtUID.Text = Convert.ToString（dr [ ID]）;
}
}
}

1. CPaini建议的一致列名;
2. 删除未使用的 DataTable 和 dt.Load（dr），如CPallini和CodeMaster_Noob所建议的那样;
3. 使用块在中包装 SqlDataReader ，并告诉它在完成时关闭连接;
4. 在尝试访问 SqlDataReader 中的值之前，添加了所需的 dr.Read（）调用;
5. 替换 dr [ID]。ToString（） with Convert.ToString（dr [ID]） ，如果列值为 null ;




Quote：

string sql = string.Format（@SELECT top 1 ID FROM用户订单ID desc）;

Quote：

txtUID.Text = dr [ UID ] .ToString（）;

我看到不匹配...




请注意， DataTable 在您的代码中没用。




what is the problem with these codes please help



string conStr = ConfigurationManager.ConnectionStrings["CStringCRM"].ToString();
            DataTable dt = new DataTable();
            SqlDataReader dr = null;
            using(SqlConnection conn = new SqlConnection(conStr))
            {
                string sql = string.Format(@"SELECT top 1 ID FROM User order by ID desc"); 
                SqlCommand cmd = new SqlCommand();
                cmd.Connection = conn;
                cmd.CommandText = sql;
                cmd.CommandType = CommandType.Text;
                conn.Open();

                dr = cmd.ExecuteReader();

                dt.Load(dr);
                txtUID.Text = dr["ID"].ToString();
                conn.Close();
                cmd = null;

            }

解决方案

Here's a fixed version of your code:

string conStr = ConfigurationManager.ConnectionStrings["CStringCRM"].ToString();

using (SqlConnection conn = new SqlConnection(conStr))
using (SqlCommand cmd = new SqlCommand(@"SELECT top 1 ID FROM User order by ID desc", conn))
{
    conn.Open();
    using (SqlDataReader dr = command.ExecuteReader(CommandBehavior.CloseConnection))
    {
        if (dr.Read())
        {
            txtUID.Text = Convert.ToString(dr["ID"]);
        }
    }
}

1. Consistent column name, as suggested by CPallini;
2. Removed the un-used DataTable and dt.Load(dr), as suggested by CPallini and CodeMaster_Noob;
3. Wrapped the SqlDataReader in a using block, and told it to close the connection when finished;
4. Added the required dr.Read() call before attempting to access values from the SqlDataReader;
5. Replaced dr["ID"].ToString() with Convert.ToString(dr["ID"]), in case the column value is null;




Quote:

string sql = string.Format(@"SELECT top 1 ID FROM User order by ID desc");




Quote:

txtUID.Text = dr["UID"].ToString();


I see a mismatch...


Please note, the DataTable is useless in your code.




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