callback 在asp.net应用实例

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1. 在button的 onclick 中写入：
   onclick="<%= clientscript.getcallbackeventreference(this,"document.getelementbyid('txtusername').value","oncallback",null) %>" 
2. 在网页特效中编写相应的函数

   function oncallbacknobtn()
           {
               callserver(document.getelementbyid('txtusername').value,"");
           }

3. 在 xxx.asp教程x.cs 中继承 icallbackeventhandler  并实现其方法。

   public partial class webpage_callbackbtn : system.web.ui.page, icallbackeventhandler
   {
       protected string struserinfo;  //callback最终得到的信息
       protected void page_load(object sender, eventargs e)
       {
       }
   
       #region icallbackeventhandler 成员
   
       public string getcallbackresult()
       {
           return struserinfo;
       }
   
       public void raisecallbackevent(string eventargument)  //服务端的处理函数
       {
           if (eventargument == "") return;
           system.data.sqlclient.sqlconnection conn = new system.data.sqlclient.sqlconnection();
           conn.connectionstring = system.web.configuration.webconfigurationmanager.connectionstrings["nowthwindconnectionstring"].connectionstring;
   
           sqlcommand cmd = new sqlcommand();
           cmd.commandtype = commandtype.text;
           cmd.parameters.add("@firstname", sqldbtype.nvarchar, 10)
               .value = eventargument;
           cmd.commandtext = "select employeeid, lastname from employees where firstname=@firstname";
           cmd.connection = conn;
   
           sqldatareader reader;
           connectionstate previousconnectionstate = conn.state;
   
           try
           {
               if (conn.state == connectionstate.closed)
               {
                   conn.open();
               }
   
               reader = cmd.executereader();
   
               using (reader)
               {
                   while (reader.read())
                   {
                       // process sprocresults datareader here.
                       struserinfo += reader[0];
                   }
               }
               struserinfo += "###";
           }
           finally
           {
               if (previousconnectionstate == connectionstate.closed)
               {
                   conn.close();
               }
           }
       }
   
       #endregion
   }

   
   raisecallbackevent() 负责接收 client 端的javascript 所传送过来的参数，以此参数查询数据库教程中的数据，最后由 getcallbackresult() 将结果传回 client端的javascript，最后将结果显示出来。
4. 完成  o(∩_∩)o~ 现在在 textbox 中输入 nancy 则会显示 1### 。如果输入的名字在数据库中没有则不显示，（我的只是完成了《圣殿祭司的asp.net教程》中的这一节的一部分）

1. 如上 3. 在 xxx.aspx.cs 中继承 icallbackeventhandler  并实现其方法。
2. 在 javascript中添加

3. 在 aspx.cs 中动态注册 javascript

   protected void page_load(object sender, eventargs e)
       {
           string cbreference = page.clientscript.getcallbackeventreference(this,"arg", "receiveserverdata", null);
           //page.clientscript.getcallbackeventreference(this,"arg", "receiveserverdata", null);
           string callbackscript;
           callbackscript = "function callserver(arg,context){" + cbreference + "};";
           //string callbackscript = "function callserver(arg,context){webform_docallback('__page',arg,receiveserverdata,null,null,false)};";
           page.clientscript.registerclientscriptblock(this.gettype(), "callserver123", callbackscript, true);
       }

4. 完成