Using the Web Application version number from an assembly (ASP.NET/C#)

Here is some code I use that supports getting the application's "main" assembly from either Web or non-web apps, you can then use GetName().Version to get the version.

It first tries GetEntryAssembly() for non-web apps. This returns null under ASP.NET. It then looks at HttpContext.Current to determine if this is a web application. It then uses the Type of the current HttpHandler - but this type's assembly might be a generated ASP.NET assembly if the call is made from with an ASPX page, so it traverses the HttpHandler's BaseType chain until it finds a type that isn't in the namespace that ASP.NET uses for its generated types ("ASP"). This will usually be a type in your main assembly (eg. The Page in your code-behind file). We can then use the Assembly of that Type. If all else fails then fall back to GetExecutingAssembly().

There are still potential problems with this approach but it works in our applications.

    private const string AspNetNamespace = "ASP";

    private static Assembly getApplicationAssembly()
    {
        // Try the EntryAssembly, this doesn't work for ASP.NET classic pipeline (untested on integrated)
        Assembly ass = Assembly.GetEntryAssembly();

        // Look for web application assembly
        HttpContext ctx = HttpContext.Current;
        if (ctx != null)
            ass = getWebApplicationAssembly(ctx);

        // Fallback to executing assembly
        return ass ?? (Assembly.GetExecutingAssembly());
    }

    private static Assembly getWebApplicationAssembly(HttpContext context)
    {
        Guard.AgainstNullArgument(context);

        object app = context.ApplicationInstance;
        if (app == null) return null;

        Type type = app.GetType();
        while (type != null && type != typeof(object) && type.Namespace == AspNetNamespace)
            type = type.BaseType;

        return type.Assembly;
    }

UPDATE: I've rolled this code up into a small project on GitHub and NuGet.

I prefer the Web.Config to store the current version of the site.

You can also try create an AssemblyInfo.cs file in the web application root that has the following:

using System.Reflection;
using System.Runtime.CompilerServices;
...
[assembly: AssemblyVersion("1.0.*")]
...

then access the value via the code like this:

System.Reflection.Assembly.GetExecutingAssembly()

Here is more informaiton on the AssemblyInfo class.

To add to the responders that have already posted. In order to get the assembly version in an ASP.Net web application you need to place a method in the code behind file similar to:

protected string GetApplicationVersion() {
    return System.Reflection.Assembly.GetExecutingAssembly().GetName().Version.ToString();
}

In the ASPX page you want to display the version number simply place:

<%= GetApplicationVersion() %>

Some info here: http://www.velocityreviews.com/forums/showpost.php?p=487050&postcount=8

in asp.net 2.0 each page is built into it own assembly, so only the dll the AssemblyInfo.cs is built into will return the correct answer. just add a static method to AssemblyInfo.cs that returns the version info, and call this method from your other pages.

-- bruce (sqlwork.com)

But I wrote a simple method to do that:

    public static string GetSystemVersion(HttpServerUtility server)
    {
        System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
        doc.Load(server.MapPath("~/web.config"));
        System.Xml.XmlNamespaceManager ns = new System.Xml.XmlNamespaceManager(doc.NameTable);
        ns.AddNamespace("bla", "http://schemas.microsoft.com/.NetConfiguration/v2.0");

        System.Xml.XmlNode node = doc.SelectSingleNode("/bla:configuration/bla:system.web/bla:authentication/bla:forms[@name]", ns);

        string projectName = "";
        if (node != null && node.Attributes != null && node.Attributes.GetNamedItem("name") != null)
            projectName = node.Attributes.GetNamedItem("name").Value; //in my case, that value is identical to the project name (projetname.dll)
        else
            return "";

        Assembly assembly = Assembly.Load(projectName);
        return assembly.GetName().Version.ToString();
    }

So, I had to get the Assembly from a referenced dll.

In the asp.NET MVC/WebAPI world, there is always going to be at least one class which inherits from System.Web.HttpWebApplication. The implementation below searches for that class.

using System;
using System.Linq;

static Assembly GetWebAssembly() => AppDomain.CurrentDomain.GetAssemblies().FirstOrDefault(a => a.GetExportedTypes().Any(t => t.BaseType?.FullName == "System.Web.HttpApplication"));

The above uses System.Linq in order to find that relationship, but this can also be implemented without.

First, we get all loaded assemblies

AppDomain.CurrentDomain.GetAssemblies()

Then, enumerate through the IEnumerable<Assembly>, and get all of the types directly located in the assembly.

a.GetExportedTypes()

Then, see if any of the types inherit from System.Web.HttpWebApplication

t.BaseType?.FullName == "System.Web.HttpApplication"

In my implementation, I ensured this code would only be called once, but if that is not guaranteed, I'd highly wrapping this in a Lazy<T> or other cached lazy load implementation as it is rather expensive to keep performing the blind search.

using System;
using System.Linq;

// original method
private static Assembly GetWebAssembly() => AppDomain.CurrentDomain.GetAssemblies().FirstOrDefault(a => a.GetExportedTypes().Any(t => t.BaseType?.FullName == "System.Web.HttpApplication"));

// lazy load implementation
private static Lazy<Assembly> _webAssembly = new Lazy<Assembly>(GetWebAssembly);
public static Assembly WebAssembly { get => _webAssembly.Value; }