Question

已有打开的与此命令相关联的 DataReader，必须首先将它关闭。

public class DBHelper
{
private static SqlConnection connection;
public static SqlConnection Connection
{
get
{
string connectionString = ConfigurationManager.ConnectionStrings["JcodeConnectionStrings"].ConnectionString;
if (connection == null)
{
connection = new SqlConnection(connectionString);
connection.Open();
}
else if (connection.State == System.Data.ConnectionState.Closed)
{
connection.Open();
}
else if (connection.State == System.Data.ConnectionState.Broken)
{
connection.Close();
connection.Open();
}
return connection;
}
}

//取所有记录
public static DataView GetTableData(string sqlString)
{
SqlDataAdapter da = new SqlDataAdapter(sqlString,Connection);
DataSet ds = new DataSet();
da.Fill(ds, "Jcode");

return ds.Tables["Jcode"].DefaultView;
}

/// <summary>
/// 实例化sqlCommand对象返回sqlDataReader
/// </summary>
/// <param name="safeSql"></param>
/// <returns></returns>
public static SqlDataReader GetReader(string safeSql)
{
SqlCommand cmd = new SqlCommand(safeSql, Connection);
SqlDataReader reader = cmd.ex.ExecuteReader();
return reader;
}

public static SqlDataReader GetReader(string sql, params SqlParameter[] values)
{
SqlCommand cmd = new SqlCommand(sql, Connection);
cmd.Parameters.AddRange(values);
SqlDataReader reader = cmd.ExecuteReader();
return reader;
}
public static int ExcuteCommand(string sql)
{
SqlCommand cmd = new SqlCommand(sql, Connection);
int result=cmd.ExecuteNonQuery();
return result;
}
**************************

行 54: {
行 55: SqlCommand cmd = new SqlCommand(safeSql, Connection);
行 56: SqlDataReader reader = cmd.ExecuteReader();
行 57: return reader;
行 58: }

InvalidOperationException: 已有打开的与此命令相关联的 DataReader，必须首先将它关闭

Answer 1

???什么问题
什么情况

Answer 2

稍微标准点的写法
SqlConnection
cn
=
null;
SqlCommand
cmd
=
null;
SqlDataReader
dr
=
null;
cn
=
new
SqlConnection();
cn.ConnectionString
=
"data
source=.;initial
catalog=oa;integrated
security=sspi";
cmd
=
new
SqlCommand("select
是否已阅
from
Msg
where
收信人='"
+
b
+
"'
and
是否已阅
='否'",
cn);
try
{
cn.Open();
SqlDataReader
dr
=
cmd.ExecuteReader();
if
(dr
!=
null)
{
if
(dr.Read())
{
Label1.Text
=
dr.GetString(0).ToString();
Label6.Text
=
"您有新短信，请注意查收！";
}
}
}
catch
(Exception
ex)
{
Response.Write(ex.Message);
}
finally
{
if
(dr
!=
null)
dr.Close();
if
(cmd
!=
null)
cmd.Dispose();
if
(cn
!=
null)
cn.Dispose();
}
程序还有很多问题不规范
比如
select
是否已阅
from
Msg
where
收信人='"
+
b
+
"'
and
是否已阅
='否'"
==
既然知道条件是
是否已阅
='否'，那就根本没必要
select
是否已阅...
改成
select
1
from
Msg
where
收信人='"
+
b
+
"'
and
是否已阅
='否'"即可
再比如
刚才使用的是拼接sql语句，已经基本被摒弃了，网上搜搜"参数化语句"和"sql注入"就知道了

Answer 3

关闭数据库连接
再来一次打开数据库连接
reader连接
我以前这样写过
很耗资源

Answer 4

你去电脑专区去问问吧，或许那里有人能给你正确的答案。