函數(shù)返回一個(gè)SqlDataReader對(duì)象

解決方法：

1.嘗試使用dataset

2.執(zhí)行數(shù)據(jù)庫(kù)操作命令SqlDataReader reader=MySQLCommand.ExecuteReader(CommandBehavior.CloseConnection);

示例：

原代碼：

//獲取書(shū)的目錄 public SqlDataReader GetBookCategories() { //創(chuàng)建數(shù)據(jù)庫(kù)連接和命令的對(duì)象 SqlConnection myConnection=new SqlConnection(ConfigurationSettings.AppSettings["ConnectionString"]); string sqlString="select CategoryID,CategoryName from BookCategories order by CategoryName ASC"; SqlCommand mySqlCommand=new SqlCommand(sqlString,myConnection); //打開(kāi)數(shù)據(jù)庫(kù)連接 myConnection.Open(); //執(zhí)行數(shù)據(jù)庫(kù)操作命令 SqlDataReader reader=mySqlCommand.ExecuteReader(); //關(guān)閉數(shù)據(jù)庫(kù)連接 myConnection.Close(); returnreader; }－－－－－－－－－－－－－－－－－－編譯錯(cuò)誤：未將對(duì)象引用設(shè)置到對(duì)象的實(shí)例。說(shuō)明: 執(zhí)行當(dāng)前 Web 請(qǐng)求期間，出現(xiàn)未處理的異常。請(qǐng)檢查堆棧跟蹤信息，以了解有關(guān)該錯(cuò)誤以及代碼中導(dǎo)致錯(cuò)誤的出處的詳細(xì)信息。異常詳細(xì)信息: System.NullReferenceException: 未將對(duì)象引用設(shè)置到對(duì)象的實(shí)例。－－－－－－－－－－－－－－－－－－

解決方法：

[WebMethod]//獲取書(shū)的目錄public SqlDataReader GetBookCategories(){//創(chuàng)建數(shù)據(jù)庫(kù)連接和命令的對(duì)象SqlConnection myConnection=new SqlConnection(ConfigurationSettings.AppSettings["ConnectionString"]);string sqlString="select CategoryID,CategoryName from BookCategories order by CategoryName ASC";SqlCommand mySqlCommand=new SqlCommand(sqlString,myConnection);//打開(kāi)數(shù)據(jù)庫(kù)連接myConnection.Open();//執(zhí)行數(shù)據(jù)庫(kù)操作命令SqlDataReader reader=mySqlCommand.ExecuteReader(CommandBehavior.CloseConnection);return reader;}