A Simplified Asynchronous Call Pattern for WinForm Applications

re: A Simplified Asynchronous Call Pattern for WinForm Applications

manish — Sat, 13 Dec 2003 06:51:00 GMT

Can this be extended/used with Web form application ???
-Manish
manishgo_in@hotmail.com

re: A Simplified Asynchronous Call Pattern for WinForm Applications

David Hill — Sun, 14 Dec 2003 07:30:00 GMT

As described, this technique will not work from a web form because the calling object has to be around when the asynchronous call finishes so the callback method can be invoked. For a web form this will not be case (unless you block the thread, which you should never do!) because it is a transient object just created to service a single web request.

There is a great article on MSDN which describes what you need to do in the WebForm case...

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnservice/html/service07222003.asp

So, if you are calling a web service, or any kind of lengthy call, from an ASPX page, then you need to do the call asynchronously from within a PreRequestHandler. It's all a bit complicated but the performance gains are worth it...

re: A Simplified Asynchronous Call Pattern for WinForm Applications

manish — Mon, 15 Dec 2003 04:59:00 GMT

Thanks a lot David for the link and explanation...
-Manish

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Hal Pierson — Thu, 08 Jan 2004 13:29:00 GMT

Generics will simplify the service agent.
In the mean time, perhaps one of the "templated" code generators could be used.

Service Agents as a best practice pattern to call Web services

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Online Software Design Pattern Links

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Patterns and Pattern Languages are ways to describe best practices, good designs, and capture experience in a way that...

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Oskar Austegard — Fri, 19 Mar 2004 14:20:00 GMT

Saw your article on MSDN - (looks promising, I gave you an 8), and the ServiceAgent class looks like a good candidate for code generation based on reflection of the underlyin WebService proxy class.

But - Is there a typo/bug in the ServiceAgent example code? Sholdn't the call in GetCustomerDataCallback be to GetCustomerDataCompletedCallback and not to GetCustomersCompletedCallback?

Thanks,

Oskar

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Derek Woo — Sat, 20 Mar 2004 14:55:00 GMT

I like your article. And in fact part of the idea is being implemented in my app in hand.

But my problem is that, there is no way, from the GUI point of view, to catch exceptions raised by the webservice proxy. Because it's now intercepted by the ServiceAgent. Probably it's possible to supply a callback for failed webservice invoke. But then that complicates the interface and looks ugly. Do you have any idea of how to solve this problem? Any way to route the exceptions back to the callback function supplied by the GUI class?

-Derek

Any chance to get AutoCallbackServiceAgent working on Compact Framework?

Mathias Fritsch — Wed, 14 Apr 2004 13:36:00 GMT

I saw the article on msdn and it worked fine. It would fit perfectly into my CFW - Project. Anybody tried to get it working?
(no Delegate.CreateDelegate )

Mathias Fritsch

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Senthil — Fri, 30 Apr 2004 18:51:00 GMT

BackgroundWorker for .NET 1.1 (www.idesign.net) can be used to solve the same problem.

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Furty — Wed, 09 Jun 2004 10:54:00 GMT

Just musing, do MS pay you when they republish your copyrighted work on MSDN, or do they simply offer you the fame/glory? :)

re: A Simplified Asynchronous Call Pattern for WinForm Applications

hak — Fri, 02 Jul 2004 22:49:00 GMT

Great article. I have one question about Asychronous call and SQL CE.
When Asychronous call comes back and updates SQL CE and UI thread is about to access SQL CE at the same time, because SQL CE allows only one connection, the application will blow up? Do you have any thought on this? Thank you

re: A Simplified Asynchronous Call Pattern for WinForm Applications

David Hill — Thu, 08 Jul 2004 08:51:00 GMT

If you can only access the database on a single thread, then you have a few options.

You could use the UI thread to update and query the database, passing data from the background thread to the UI thread for it to update the UI and access the local database. This is not very elegant and using the UI thread to update and access a database is generally to be avoided, but if the database is local then you might get away with it.

The alternative is to create a single background thread which is responsible for managing the database and then use this to query and update the database. Both the UI and other background threads will interact with this manager thread to get data into and out of the database.

I guess a third option would be to close and re-open the connection for each time you access the database...

re: A Simplified Asynchronous Call Pattern for WinForm Applications

Sergio — Mon, 12 Jul 2004 18:16:00 GMT

I am guessing this will not work in the .net compact framework. Is that true? Are there other options?

thanks

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