Async method raised in web page doesn't refresh page

Discussion in 'ASP .Net' started by TS, Jul 26, 2005.

  1. TS

    TS Guest

    Im in a web page and call an asynchronous method in business class. the call
    back method is in the web page.

    When page processes, it runs thru code begins invoking the method then the
    page unloads. When the callback method is raised, only the method in the web
    page is run and the page never refreshes, it seems it all happens on the
    server side.

    I am trying to refresh the constrols on the page inside the callback method,
    but when id do, it isn't flushed to the browser.

    Anyone know how i can do this with this long running async thread?

    thanks a bunch!
     
    TS, Jul 26, 2005
    #1
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  2. TS

    Marina Guest

    Right, it happens asynchronously. By the time it does a call back, the page
    has no doubt finished processing, sent the results back to the client, and
    has been displayed in the browser. The request is finished, the connection
    is over.


    "TS" <> wrote in message
    news:OF%...
    > Im in a web page and call an asynchronous method in business class. the
    > call
    > back method is in the web page.
    >
    > When page processes, it runs thru code begins invoking the method then the
    > page unloads. When the callback method is raised, only the method in the
    > web
    > page is run and the page never refreshes, it seems it all happens on the
    > server side.
    >
    > I am trying to refresh the constrols on the page inside the callback
    > method,
    > but when id do, it isn't flushed to the browser.
    >
    > Anyone know how i can do this with this long running async thread?
    >
    > thanks a bunch!
    >
    >
     
    Marina, Jul 26, 2005
    #2
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  3. TS

    Brock Allen Guest

    It's because the page has already completed rendering to the browser by the
    time the aserver async event is raised. You need to have the page wait around
    until the async work is done before it completes its rendering. Are you working
    in 1.1 or 2.0? Fritz has an article on how to achieve this in v1.1:

    http://msdn.microsoft.com/msdnmag/issues/03/06/Threading/default.aspx

    In 2.0 this is somewhat better integrated at the page level with the Async
    Page feature.

    -Brock
    DevelopMentor
    http://staff.develop.com/ballen



    > Im in a web page and call an asynchronous method in business class.
    > the call back method is in the web page.
    >
    > When page processes, it runs thru code begins invoking the method then
    > the page unloads. When the callback method is raised, only the method
    > in the web page is run and the page never refreshes, it seems it all
    > happens on the server side.
    >
    > I am trying to refresh the constrols on the page inside the callback
    > method, but when id do, it isn't flushed to the browser.
    >
    > Anyone know how i can do this with this long running async thread?
    >
    > thanks a bunch!
    >
     
    Brock Allen, Jul 26, 2005
    #3
  4. TS,

    You can't perform asynchronous operations on a web server like this and
    expect the page to be refreshed accordingly. You will need to have your
    operation complete, and then store the results of that operation on the
    server.

    Then, on the client side, you will have to poll some page over and over
    again until the operation completes. When it does, you can get the results
    and post them on the page accordingly.

    You might also want to look into using XML on the page itself,
    specifically, using the XML parser in javascript to load your data, and
    update using dynamic HTML.

    Hope this helps.


    --
    - Nicholas Paldino [.NET/C# MVP]
    -

    "TS" <> wrote in message
    news:OF%...
    > Im in a web page and call an asynchronous method in business class. the
    > call
    > back method is in the web page.
    >
    > When page processes, it runs thru code begins invoking the method then the
    > page unloads. When the callback method is raised, only the method in the
    > web
    > page is run and the page never refreshes, it seems it all happens on the
    > server side.
    >
    > I am trying to refresh the constrols on the page inside the callback
    > method,
    > but when id do, it isn't flushed to the browser.
    >
    > Anyone know how i can do this with this long running async thread?
    >
    > thanks a bunch!
    >
    >
     
    Nicholas Paldino [.NET/C# MVP], Jul 26, 2005
    #4
  5. > Then, on the client side, you will have to poll some page over and
    > over
    > again until the operation completes. When it does, you can get the
    > results
    > and post them on the page accordingly.
    >

    The server side code can ask the client to refresh like this:

    // Ask client to refresh every 3 seconds
    Response.AppendHeader("Refresh", "3");

    Next, you have to find a way to pass the results from the asynchronous
    callback to the web page. I did this by passing the Session object in the
    IAsyncResult.AsyncState field. The Session object can then be accessed
    from both the web page and the asynchronous callback function.

    Works nicely, but watch out for concurrency issues...

    Greetings,
    Wessel
     
    Wessel Troost, Jul 26, 2005
    #5
  6. TS

    TS Guest

    I don't see how you can use the session in the async method, because that
    method is the start of the new thread that doesn't has access to HTTPContext
    object. Are you saying that you are passing the session object to the async
    method and NOT that you are using the session object in async method and set
    its return value to the session object?

    thanks for your posts.

    "Wessel Troost" <> wrote in message
    news:eek:p.sujfpza5f3yrl7@asbel...
    > > Then, on the client side, you will have to poll some page over and
    > > over
    > > again until the operation completes. When it does, you can get the
    > > results
    > > and post them on the page accordingly.
    > >

    > The server side code can ask the client to refresh like this:
    >
    > // Ask client to refresh every 3 seconds
    > Response.AppendHeader("Refresh", "3");
    >
    > Next, you have to find a way to pass the results from the asynchronous
    > callback to the web page. I did this by passing the Session object in the
    > IAsyncResult.AsyncState field. The Session object can then be accessed
    > from both the web page and the asynchronous callback function.
    >
    > Works nicely, but watch out for concurrency issues...
    >
    > Greetings,
    > Wessel
     
    TS, Jul 26, 2005
    #6
  7. TS

    TS Guest

    thanks for all the feedback. There seems to be some potential here.


    "TS" <> wrote in message
    news:OF%...
    > Im in a web page and call an asynchronous method in business class. the

    call
    > back method is in the web page.
    >
    > When page processes, it runs thru code begins invoking the method then the
    > page unloads. When the callback method is raised, only the method in the

    web
    > page is run and the page never refreshes, it seems it all happens on the
    > server side.
    >
    > I am trying to refresh the constrols on the page inside the callback

    method,
    > but when id do, it isn't flushed to the browser.
    >
    > Anyone know how i can do this with this long running async thread?
    >
    > thanks a bunch!
    >
    >
     
    TS, Jul 26, 2005
    #7
  8. Hi TS,

    AS for async processing in ASP.NET web application, direclty use the .net
    delegation's Beginxxx call won't work quite work since when the underlying
    working thread complete executing, the original httpRequest(in fact the
    whole Httpcontext) may already been disposed. So currently two possible
    async means we can choose are:
    1. make a central async processing httphandler which do the time consuming
    task. And we call this handler in the clientside page through clientside
    script (using MSXML.XMLHTTP component) and pull data from serverside so as
    to refresh our page.

    2. consider adjusting our page's design and using the asp.net's buildin
    page/handler level async processing model. The following msdn article(as
    also mentioend by Brock ) has demonstarte this mode:

    http://msdn.microsoft.com/msdnmag/issues/03/06/Threading/default.aspx

    Hope helps. Thanks,

    Steven Cheng
    Microsoft Online Support

    Get Secure! www.microsoft.com/security
    (This posting is provided "AS IS", with no warranties, and confers no
    rights.)

    --------------------
    | From: "TS" <>
    | References: <OF#>
    <> <op.sujfpza5f3yrl7@asbel>
    | Subject: Re: Async method raised in web page doesn't refresh page
    | Date: Tue, 26 Jul 2005 16:37:39 -0500
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    |
    | I don't see how you can use the session in the async method, because that
    | method is the start of the new thread that doesn't has access to
    HTTPContext
    | object. Are you saying that you are passing the session object to the
    async
    | method and NOT that you are using the session object in async method and
    set
    | its return value to the session object?
    |
    | thanks for your posts.
    |
    | "Wessel Troost" <> wrote in message
    | news:eek:p.sujfpza5f3yrl7@asbel...
    | > > Then, on the client side, you will have to poll some page over and
    | > > over
    | > > again until the operation completes. When it does, you can get the
    | > > results
    | > > and post them on the page accordingly.
    | > >
    | > The server side code can ask the client to refresh like this:
    | >
    | > // Ask client to refresh every 3 seconds
    | > Response.AppendHeader("Refresh", "3");
    | >
    | > Next, you have to find a way to pass the results from the asynchronous
    | > callback to the web page. I did this by passing the Session object in
    the
    | > IAsyncResult.AsyncState field. The Session object can then be accessed
    | > from both the web page and the asynchronous callback function.
    | >
    | > Works nicely, but watch out for concurrency issues...
    | >
    | > Greetings,
    | > Wessel
    |
    |
    |
     
    Steven Cheng[MSFT], Jul 27, 2005
    #8
  9. > I don't see how you can use the session in the async method, because that
    > method is the start of the new thread that doesn't has access to
    > HTTPContext object.


    Accessing the HTTPContext from another thread might be OK, but I don't
    think you can call it from an asynchronous callback. The context may not
    be valid anymore when the callback is invoked.

    But the Session is available to other threads for sure; the next thread
    might be handled by another ASP.NET worker thread, after all.

    > Are you saying that you are passing the session object to the async
    > method and NOT that you are using the session object in async methodand
    > set its return value to the session object?
    >

    Actually I'm passing a reference to a data structure, like:

    Context.Session[ "MyDataObject" ] = MyData;
    AsyncCallback callback = new AsyncCallback( MyCallback );
    BeginMyMethod( ..., callback, MyData );

    The callback function looks like:

    public static void MyCallback( IAsyncResult ar )
    {
    MyData = (MyDataClass) ar.AsyncState;
    // Store results in MyData here.
    // The Web Page can retrieve the results using
    // Session["MyDataObject"].
    }

    Even if the Session ends, the MyData object will still exist.

    Greetings,
    Wessel
     
    Wessel Troost, Jul 27, 2005
    #9
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