Async method raised in web page doesn't refresh page

[TS]

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]

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.

 

[Brock Allen]

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.

 

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

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.

 

[Wessel Troost]

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]

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.

 

[TS]

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

 

[Steven Cheng[MSFT]]

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" <[email protected]>
| References: <OF#[email protected]>
<[email protected]> <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.
|
| | > > 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]

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