Introduction to Asp.net and comet development, the first example

Comet (reverse Ajax) is mainly used to maintain the connection with the server through HTTP persistent connections, and implement server push and bidirectional communication.

Benefits: 1. Resource Saving and low latency compared with Ajax polling. 2. Compared with websocket, it is widely used.

 

1. Create an empty Asp.net MVC project first

Add a controllerCodeIt can also be used in Asp.net webform)

     Public   Class Cometcontroller: Controller
{
 Public Actionresult test ()
{
Response. Buffer = False ;
 While (True )
{
Response. Write (datetime. Now. tostring ( "  Yyyy-mm-dd hh: mm: SS fff  " ) + "  |  " );
Thread. Sleep ( 500 );
}
 //  Cannot run here  
              Return Content ( "" );
}
}
}

 

2. Create a controller and view to display HTML

View code

 
Public ClassHomecontroller: Controller
{
//
//Get:/home/

PublicActionresult index ()
{
ReturnView ();
}

}
 

View code is important

@{
Layout = NULL;
}
 <!  Doctype html  > 
 <  Html  > 
 <  Head  > 
 <  Title  > Index </  Title  > 
<  Script  Type  = "Text/JavaScript"  SRC  = "Http://code.jquery.com/jquery-1.7.1.min.js"  > </  Script  > 
 <  Script  Language  = "JavaScript"  >  
 VaR  REQ  =   False  ;
  VaR  Lastdelimiterposition  =   -  1  ;

$ (Document). Ready ( Function  (){
Getdata ();
});

  Function  Getdata (){
Loadxmldoc (  "  /Comet/test  "  );
}

  //  Create an xhr instance 
  Function  Createrequest (){
  If  (Window. XMLHttpRequest  &&   !  (Window. activexobject )){
  Try  {
REQ  =  New  XMLHttpRequest ();
}  Catch  (E ){
REQ  =   False  ;
}  //  Branch for IE/Windows ActiveX version  
 }  Else   If  (Window. activexobject ){
  Try  {Req  =   New  Activexobject (  "  Msxml2.xmlhttp "  );}  Catch  (E ){
  Try  {
REQ  =   New  Activexobject (  "  Microsoft. XMLHTTP "  );
}  Catch  (E ){
REQ  =   False  ;
}
}
}
}

  //  Initiate a request  
 Function  Loadxmldoc (URL ){
  Try  {
  If  (Req ){
Req. Abort ();
REQ  =   False  ;
}
Createrequest ();
  If (Req ){
Req. onreadystatechange  =  Processreqchange;
Req. Open (  "  Get  "  , URL,  True  );
Req. Send (  "" );
}  Else  {
Alert (  '  Unable to create request  '  );
}
}  Catch  (E) {alert (E. Message );}
}

  // Check status  
  Function  Processreqchange (){
  If  (Req. readystate  =   3  ){
  Try  {
Processinput (req. responsetext );
 If  (Req. responsetext. Length  >   3000  ){
Lastdelimiterposition  =   -  1  ; Getdata ();
}
}
  Catch (E ){
Alert (E. Message );
}
}
}


  //  Split string  
  Function  Processinput (input ){
  VaR  Text  =  Input;
 VaR  Nextdelimiter  =  Text. indexof (  '  |  '  , Lastdelimiterposition  +   1  );
 If  (Nextdelimiter  ! =   -  1  ){
  VaR  Timestamp  =  Text. substring (nextdelimiter  +  1  );
  If  (Timestamp. Length  >   0  ){
Lastdelimiterposition  =  Nextdelimiter;
Processtime (timestamp );
}
}
}

  // Event output or triggered  
  Function  Processtime (time ){
Document. getelementbyid (  '  Div1  '  ). Innerhtml  =  Time;
}
  </ Script  > 
 </  Head  > 
 <  Body  > 
 <  Div  > 
 <  Div  ID  = "Div1"  > 
</  Div  > 
 <  Div  ID  = "Div2"  > 
 </  Div  > 
 </  Div  > 
 </  Body > 
 </  Html  > 

3. The final result is:

A time is displayed on the page, updated every half second

Of course, after you get the content, you can do what you want... Update Dom or execute Js. (fortunately, the eval method is used ~~)

 

4. This example is just an implementation based on Asynchronous JavaScript,

In fact, you can also use the <IFRAME> and <SCRIPT> labels. In particular, the script tag can access and execute cross-domain JavaScript.

 

Http://en.wikipedia.org/wiki/Comet_ (programming)

Some libraries may be used here: ASP. NET comet Ajax Library (reverse Ajax-server push) http://pokein.codeplex.com/