ASP.NET: Getting the client's .NET version

Blogged by Björn Meyer on September 19, 2007 and tagged with BrowserTextControl.

To use TX Text Control .NET Server's BrowserTextControl in the Internet Explorer, the .NET Framework must be installed on client-side. A client-side control is required to provide the true WYSIWYG editing interface.

If no .NET Framework is installed, you might redirect your users to a download and install page for all prerequisites.

If you want to avoid external controls or Javascript to check whether a .NET Framework is installed, there is only one way to get this information from the client: Using the user agent information the browser discloses. Using the HTTP server variables, a string can be requested that describes the browser in detail.

Request.ServerVariables["HTTP_USER_AGENT"]

This returns a string like this:

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR 2.0.50727; .NET CLR 3.0.04506; .NET CLR 1.1.4322; InfoPath.1)

It shows that my machine is running Windows Vista (NT 6.0), I am browsing with Internet Explorer 7.0 and that 3 versions of the .NET Framework are installed: 1.1, 2.0 and 3.0.

Now, we simply need to split the returned string to get the specific versions.

ArrayList agentVariables = new ArrayList(Request.ServerVariables["HTTP_USER_AGENT"].Split(';'));
foreach (string variable in agentVariables)
{
    if (variable.StartsWith(" .NET"))
        ListBox1.Items.Add(variable.Trim());
}

The above code fills a list box with the available .NET Frameworks.