Question

While looking for a way to change the user agent string for the webBrowser control, I found this nifty method:

    [DllImport("urlmon.dll", CharSet = CharSet.Ansi)]
    private static extern int UrlMkSetSessionOption(int dwOption, string pBuffer, int dwBufferLength, int dwReserved);
    const int URLMON_OPTION_USERAGENT = 0x10000001;

    public static void ChangeUserAgent(string Agent)
    {
        UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, Agent, Agent.Length, 0);
    }

Basically, I needed a way to change the user agent until I want to change it again.

The usual:

webBrowser1.Navigate ("http://www.whatsmyuseragent.com", "_self" , null, "User-Agent: Luke's Web Browser");

Only works for one request.

However, I keep reading everywhere that the first method only works once per session. In my case, it works as many times as I want it to. So my guess is that this is related to the instance of Internet Explorer on the computer?

So my questions are:

• What version does the end user need to have installed on their computer for this method to work as intended? IE. change as much as I want.
• Since this is related to the Internet Explorer installed on the computer, does changing the user agent in my application effect the browser?
• If the user has Internet Explorer open, will this method still work?

Thanks!

Answer 1

We use the “UrlMkSetSessionOption” function quite a bit. We have a “custom web browser shell” which is really just an IE user control embedded into a full screen WinForms program. We change the user agent to identify to our web server that this is our “custom” browser shell. But to answer your specific questions:

1. We’ve used this with both IE8 on XP and IE9 on Win7. I think it is version independent, but we always use the latest version.
2. As far as we can tell, changing this setting only affects IE running in the process that invoked the method. So if a user launches IE from the desktop, the user agent is unchanged. If you restart the program, the user agent is unchanged.
3. It works with and without standalone IE instances running. The user agent for those standalone instances remain unchanged.