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 find that the simplest one-liner way to get the version of your "main" assembly (instead of the dynamic one) is:

typeof(MyMainClass).Assembly.GetName().Version

Use your top-level class, which isn't likely to ever "change its meaning" or to be replaced as part of a refactoring effort, as MyMainClass. You know in which assembly this very class is defined and there can no longer be confusion as to where the version number comes from.

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() %>