Question

I have an ASP.NET website and a seperate C# application. The application writes data to a file, the website populates the treeview with the data in the file. I populate the treeview in the page Load event.

The website checks if the file has changed. This happens from a code behind file. If the file did change, the website needs to be refreshed. I cannot use Response.Redirect because I get a

Response is not available in this context

I tried System.Web.HttpContext.Current.Response.Redirect, but this gives me a NullReference.

How can I refresh the page from a code behind file, so that it loads the right data in the treeview? Other suggestions that work but use something else than refreshing the page are welcome. Thanks in advance!

Edit: The actual problem is dynamically updating the treeview (new data = updated treeview). I have tried to do something with data from a MySql database but failed. The idea is the same, except the data isn’t coming from a file but from a database. I added this because I thought this info might help users understand my problem.

Answer 1

you can’t send data to the client from an initiative of the server.

You will have to poll (jQuery/ajax) if new data is available, then refresh from the client side.

this involves basically :

• on the server
  • a web service, webmethod page method, custom handler, etc. that can tell if new data is available
• on the client
  • a timer that query the server if data is refreshed, and, in this case, that refresh the page, or reconstruct the DOM if using some JS templating

[Edit] a bit of background :

Actually, System.Web.HttpContext.Current.Response is null because of the asynchronous model of the Http protocol. The browser emits a request “http://srv/resource”, the server intercept it on the port 80 (by default), parse the request, build a response (mostlya bunch of html content) and send the response the browser. Then the connection is closed. This choice allows a great scalability, as it does not requires to keeps thousands of connections alive with nearly no data passing on it.

The impact of this, is that the web server have to knowledge of the client, other than what is send in the request. The server receive text, and send text in return.

Microsoft has created the ASP.Net framework to reproduce the RAD feeling of desktop applications. You think with controls and events, not in producing html flow like ASP or PHP. They succeeded in the sense, that, building web apps are quite similar to desktop development.

The quite is actually what is causing you some confusion. Even if the asp.net framework encapsulate most of the plumbing (viewstate is the key) to simulate this behavior, asp.net will, at least, still be a parser for request text that produces a html text to send to the client, in one shot.

So you have to cheat. You can, as I suggested, automate the browser (using javascript) to wrap this asynchronous work into a “dynamic” application.