ASP.NET – AppDomain.CurrentDomain.GetAssemblies() – Assemblies missing after AppDomain restart

I looked through the ASP.NET MVC 2.0 source code and looked up how AreaRegistration.RegisterAllAreas(); is implemented. This line is usually put into the Global.asax Application_Start() method and internally it scans all Assemblies for types that implement the AreaRegistration abstract type. This is kinda the behaviour I’m after.

It appears RegisterAllAreas() makes a call to BuildManager.GetReferencedAssemblies(), well if it’s good enough for MVC then it’s good enough for me 🙂

I’ve done some experimentation and BuildManager.GetReferencedAssemblies() will even pick up adhoc, random DLL’s dropped into the /bin folder, even with no references to any projects in the Visual Studio solution. So it appears far more reliable than AppDomain.Current.GetAssemblies().

I’ve rewritten my Assembly locator code to the following:

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Web;
using System.Web.Compilation;

public static class AssemblyLocator
{
    private static readonly ReadOnlyCollection<Assembly> AllAssemblies;
    private static readonly ReadOnlyCollection<Assembly> BinAssemblies;

    static AssemblyLocator()
    {
        AllAssemblies = new ReadOnlyCollection<Assembly>(
            BuildManager.GetReferencedAssemblies().Cast<Assembly>().ToList());

        IList<Assembly> binAssemblies = new List<Assembly>();

        string binFolder = HttpRuntime.AppDomainAppPath + "bin\\";
        IList<string> dllFiles = Directory.GetFiles(binFolder, "*.dll",
            SearchOption.TopDirectoryOnly).ToList();

        foreach (string dllFile in dllFiles)
        {
            AssemblyName assemblyName = AssemblyName.GetAssemblyName(dllFile);

            Assembly locatedAssembly = AllAssemblies.FirstOrDefault(a =>
                AssemblyName.ReferenceMatchesDefinition(
                    a.GetName(), assemblyName));

            if (locatedAssembly != null)
            {
                binAssemblies.Add(locatedAssembly);
            }
        }

        BinAssemblies = new ReadOnlyCollection<Assembly>(binAssemblies);
    }

    public static ReadOnlyCollection<Assembly> GetAssemblies()
    {
        return AllAssemblies;
    }

    public static ReadOnlyCollection<Assembly> GetBinFolderAssemblies()
    {
        return BinAssemblies;
    }
}