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

Question

How do I obtain the version number of the calling web application in a referenced assembly?

I've tried using System.Reflection.Assembly.GetCallingAssembly().GetName() but it just gives me the dynamically compiled assembly (returning a version number of 0.0.0.0).

UPDATE: In my case I needed a solution that did not require a reference back to a class within the web application assembly. Jason's answer below (marked as accepted) fulfils this requirement - a lot of others submitted here don't.

Answer 1

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.