ExecuteScalar 要求已打开且可用的连接。连接的当前状态为已关闭
问题是：我已经在每次用完DataReader后，都把对应的DataReader关闭了，同时他们共用一个SqlConnection，不过我每次用时，都把CommandText改过来了，可是还是出现这个错误提示，请高手指点。
this.Exsql.Open();
string cmdText = " ";
string text2 = " ";
string text3 = " ";
string text4 = " ";
string text5 = " ";
cmdText = "select DISTINCT YX_ProID from YX_Shoping ";
SqlCommand com = new SqlCommand(cmdText, this.Exsql.con);
SqlDataReader reader = com.ExecuteReader();
DataSet set = new DataSet();
DataTable table = new DataTable( "tab1 ");
set.Tables.Add(table);
DataColumn column = new DataColumn( "YX_ID ", Type.GetType( "System.Int32 "));
set.Tables[ "tab1 "].Columns.Add(column);
column = new DataColumn( "YX_ProName ", Type.GetType( "System.String "));
set.Tables[ "tab1 "].Columns.Add(column);
column = new DataColumn( "YX_ProNum ", Type.GetType( "System.Int32 "));
column.DefaultValue = 0;
set.Tables[ "tab1 "].Columns.Add(column);
column = new DataColumn( "YX_ProPic ", Type.GetType( "System.String "));
set.Tables[ "tab1 "].Columns.Add(column);

int Lenreader = -1;
Hashtable hashtable = new Hashtable();

while (reader.Read())
{
Lenreader++;
hashtable.Add(Lenreader, reader[0].ToString());

}
reader.Close();

for (int i = 0; i <= Lenreader;i++ )
{
com.CommandText= "Select sum(YX_OrderProNum) from YX_Shoping where YX_ProID= ' " + hashtable[i].ToString() + " ' ";
int num = Convert.ToInt32(com.ExecuteScalar());
com.CommandText= "Select YX_ProID,YX_ProName from YX_Shoping where YX_ProID= ' " + hashtable[i].ToString() + " ' ";
SqlDataReader reader2 = com.ExecuteReader();
string text8 = " ";
string text9 = " ";
int num2 = 0;
if (reader2.Read())
{
text8 = reader2[ "YX_ProName "].ToString();
num2 = Convert.ToInt16(reader2[0].ToString());
}
string Insreader2 = reader2[0].ToString();
reader2.Close();

com.CommandText= "select YX_Spic from YX_Product where YX_ID= " + Convert.ToInt16(Insreader2);
SqlDataReader reader3 = com.ExecuteReader(CommandBehavior.CloseConnection);
if (reader3.Read())
{
text9 = reader3[0].ToString();
}

DataRow row = table.NewRow();
row[0] = num2;
row[1] = text8;
row[2] = num;
row[3] = text9;
table.Rows.Add(row); reader3.Close();
}

table.DefaultView.Sort = "YX_ProNum desc ";
DataRowCollection rows = table.Rows;
int count = table.Rows.Count;
if (count != 0)
{
text2 = rows[0][ "YX_ProPic "].ToString();
text3 = rows[0][ "YX_ID "].ToString();
text4 = rows[0][ "YX_ProName "].ToString();
if (text3 == " ")
{

text3 = "0 ";
}
int num4 = 1;
for (int i = 1; i < count; i++)
{
if (num4 > = 10)
{
break;
}
string text11 = text5;
text5 = text11 + " <TR> <TD bgColor= '#cccccc ' colSpan= '2 ' height=1> </TD> </TR> \n <TR> \n <TD onmouseover=\ "this.style.backgroundColor= '#EDEBEF '\ " style=\ "CURSOR: ' hand '; HEIGHT: '21px '; BACKGROUND-COLOR: '#ffffff '\ " onmouseout=\ "this.style.backgroundColor= '#FFFFFF '\ " align=left colSpan=2 height=21> \n <a href={$Hope_SitUrl$}ShowProduct.aspx?YX_MID= " + rows[i][ "YX_ID "].ToString() + " style= 'color:#676767 '> " + newstr(rows[i][ "YX_ProName "].ToString(), 12) + " </a> \n </TD> </TR> \n ";
num4++;
}
}
this.Exsql.Close();

public class YX_sql
{
public SqlConnection con;
public YX_sql()
{
this.con = new SqlConnection(System.Configuration.ConfigurationSettings.AppSettings[ "YXPath "]);
}

}

[解决办法]
CloseConnection
受 .NET Framework 精简版的支持。
在执行该命令时，如果关闭关联的 DataReader 对象，则关联的 Connection 对象也将关闭。