Wednesday, April 20, 2011

Calling a method in an ASP.NET application from a Windows application

Other than using a web service, is there anyway to call a method in a web app from a windows application? Both run on the same machine.

I basically want to schedule a job to run a windows app which updates some file (for a bayesian spam filter), then I want to notify the web app to reload that file.

I know this can be done in other ways but I'm curious to know whether it's possible anyway.

From stackoverflow
  • You can make your windows app connect to the web app and do a GET in a page that responds by reloading your file, I don't think it is strictly necessary to use a web service. This way you can also make it happen from a web browser.

  • A Web Service is the "right" way if you want them to communicate directly. However, I've found it easier in some situations to coordinate via database records. For example, my web app has bulk email capability. To make it work, the web app just leaves a database record behind specifying the email to be sent. The WinApp scans periodically for these records and, when it finds one with an "unprocessed" status, it takes the appropriate action. This works like a charm for me in a very high volume environment.

    You cannot quite do this in the other direction only because web apps don't generally sit around in a timing loop (there are ways around this but they aren't worth the effort). Thus, you'll require some type of initiating action to let the web app know when to reload the file. To do this, you could use the following code to do a GET on a page:

    WebRequest wrContent = WebRequest.Create("");
    Stream objStream = wrContent.GetResponse().GetResponseStream();
    // I don't think you'll need the stream Reader but I include it for completeness
    StreamReader objStreamReader = new StreamReader(objStream);

    You'll then reload the file in the PageLoad method whenever this page is opened.

  • How is the web application loading the file? If you were using a dependency on the Cache object, then simply updating the file will invalidate the Cache entry, causing your code to reload that entry when it is found to be null (or based on the "invalidated" event).

    Otherwise, I don't know how you would notify the application to update the file.

    Kev : Why the downvote? seems a reasonable approach
    John Saunders : I have no idea why certain downvotes happen. In this case, I can only guess someone didn't like "otherwise, I don't know how".
  • An ASP.NET application only exists as an instance to serve a request. This is why web services are an easy way to handle this - the application has been instantiated to serve the service request. If you could be sure the instance existed and got a handle to it, you could use remoting. But without having a concrete handle to an instance of the application, you can't invoke the method directly.

    There's plenty of other ways to communicate. You could use a database or some other kind of list which both applications poll and update periodically. There are plenty of asynchronous MQ solutions out there.

  • So you'll create a page in your webapp specifically for this purpose. Use a Get request and pass in a url parameter. Then in the page_load event check for this paremter. if it exists then do your processing. By passing in the parameter you'll prevent accidental page loads that will cause the file to be uploaded and processed when you don't want it to be.

    From the windows app make the url Get request by using the .Net HttpWebRequest. Example here:


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