Comments on: Adding “Check for update” feature to your C# application

By: mech

mech — Tue, 10 Aug 2010 08:31:47 +0000

Steve,
Your C# compiler seems to be more strict :) Please try initializing the variable before the try…finally block like this:
XmlTextReader reader = null;

By: Steve

Steve — Sat, 24 Jul 2010 14:49:55 +0000

I get a error here:

finally
{
if (reader != null) reader.Close();
}

It says “Error use of unsigned local variable “reader”

By: Jorge Sierra

Jorge Sierra — Mon, 26 Apr 2010 19:05:59 +0000

Well, I did some test and it works great.
Let me include it on my project.

By: miliu

miliu — Wed, 03 Mar 2010 15:10:53 +0000

Thanks for the nice article. I found it when I try to make VS publishing and CheckForUpdate work together. Do you have any thought on that?

By the way, on parsing out the version info from the xml file, it would be much easier using XPath. e.g.
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(xmlUrl);
Version version = new Version(xmlDoc.SelectSingleNode(“/ourfancyapp/version”).InnerText);
string url = xmlDoc.SelectSingleNode(“/ourfancyapp/url”).InnerText;

By: Fullmetal

Fullmetal — Mon, 25 Jan 2010 19:15:49 +0000

I used this code along with a downloader request code, and now the application checks the XML, and if there is an update, will ask if its OK to download it. it will then download it and install the Update. I am planning on adding a “update from USB drive” option that will check the drive for the XML file, and if the version is a newer one, install the update package from the USB drive.

By: mech

mech — Tue, 19 Jan 2010 11:38:19 +0000

Hello,

@OverTech: Yes, indeed, HttpWebRequest gives you more tcp/ip control than XmlTextReader does. I’ve checked your code snippet and it seems fine to be, well done :)

@Ranhiru: You should host two files: the XML and your installer for the new version, so users can download it. Luckily there are some free web hosting services that allow you to do so.

By: Ranhiru

Ranhiru — Sat, 16 Jan 2010 14:15:10 +0000

This is really interesting!!! Just what i was looking for :D
I was really keen on using ClickOnce but this is much much more easy and neat! I just have to host the XML file somewhere :D

Thanx a lot :) :)

By: OverTech

OverTech — Wed, 06 Jan 2010 14:51:46 +0000

Great stuff..! :)

I implemented this in my own application and ran into a small inconvenience. My users are usually connected to their office on Cisco VPN which blocks most web addresses, including the URL where my XML is located. XmlTextReader.MoveToContent will return an exception fairly quickly if there is no network connection at all, but if the user is on VPN it takes about 60 seconds before it errors out.

So instead of giving XmlTextReader the URL of the XML file, I created an HttpWebRequest with a modest timeout value then used the GetResponseStream with the XmlTextReader.

# string xmlURL = “http://domain/app_version.xml”;
# HttpWebRequest hwRequest = (HttpWebRequest)WebRequest.Create(xmlURL);
# hwRequest.Timeout = 5000;
# HttpWebResponse hwResponse = null;
# XmlTextReader reader = null;
# try
# {
# hwResponse = (HttpWebResponse)hwRequest.GetResponse();
# reader = new XmlTextReader(hwResponse.GetResponseStream());
# reader.MoveToContent();
# …
# }
# finally
# {
# if (reader != null) reader.Close();
# if (hwResponse != null) hwResponse.Close();
# }

Are there any pitfalls with this method that I might be overlooking?

Dave

By: Mark

Mark — Wed, 09 Dec 2009 14:05:55 +0000

Very nice example. Clean and straight to the point.

By: mech

mech — Fri, 20 Nov 2009 23:11:14 +0000

John,
Thank you for pointing this out, you are absolutely right – the reader should be closed in both cases – when everything is OK and when an exception occurred during parsing. And try…finally is of course the way to do it. I’ve modified the example to follow your good-practice advice :)