How to get a Reference to all Assemblies in the \bin Folder

14 September 2010 - 12:40 AM / by Dominic Pettifer. 2 Comments for How to get a Reference to all Assemblies in the \bin Folder.

Technical Article - Something I’ve been stuck on for a while is a reliable way to get a list of all Assemblies (DLL files) that are located in the ASP.NET website’s \bin folder. I’ve frequently needed this for IOC style Controller registration code (find all types in all Assemblies that implement IController for instance), or for my ASP.NET Bootstrapper pattern (find all types that implement IBootstrapperTask). Relying on AppDomain.CurrentDomain.GetAssemblies () can be dangerous as I’ll discuss.

AppDomain.CurrentDomain.GetAssemblies() Considered Armed and Extremely Dangerous

If you look at my previous blog posts on IOC containers and the Bootstrapper pattern, you’ll find that I’ve frequently had a need to locate all types in all assemblies that implement a certain interface, or derive from a particular abstract base class (such as IController for an IOC powered Controller factory, or IBootstrapperTask for the Bootstrapper). The idea is that the caller has maximum flexibility over where they put these classes, the ControllerFactory or Bootstrapper will just find them.

Frequently I’ve run into the problem of how to get a list of all these Assemblies. There are a number of ways to get references to currently loaded Assemblies such as:

Assembly.GetExecutingAssembly();

...that gets the Assembly the currently executing code resides in, or:

Assembly.GetCallingAssembly();

...that gets the Assembly that called the code that is currently executing.

To get all Assemblies you might be tempted to write:

IList<Assembly> assemblies = AppDomain.CurrentDomain.GetAssemblies();

...which gets all "currently loaded" Assemblies. However, this is dangerous because of the key phrase "currently loaded". The .NET runtime will load assemblies on demand as code from those assemblies is executed. If I’m trying to find all IBootstrapperTask or IController types in some Application_Start code, the assemblies that contain the necessary types might not have been loaded yet, so we’ll be missing some Tasks or Controllers.

I was tripped up on this, as some strange .NET runtime behaviour meant AppDomain.CurrentDomain.GetAssemblies() returned all assemblies when the application was first run, as I wanted. But after the first AppDomain restart, the normal .NET runtime dynamic assembly loading behaviour kicked in. It failed to load the assemblies containing the bootstrapper tasks and MVC Controllers, and my ASP.NET MVC application, that I deployed live, promptly crashed, doh!

Use BuildManager.GetReferencedAssemblies() Instead

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 for a brand new MVC app, and internally it scans all assemblies for types that implement the AreaRegistration abstract type, for registering Areas. This is exactly 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 did some experimentation and BuildManager.GetReferencedAssemblies() doesn’t suffer from the same dynamic assembly loading problem. It 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.CurrentDomain.GetAssemblies().

So we have a way to get a reference to all assemblies and avoid the dreaded dynamic assembly loading problem, but what about getting a reference to just assemblies in the \bin folder. I wrote a handy AssemblyLocator utility function:

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

namespace MvcLibrary.Ioc
{
    public static class AssemblyLocator
    {
        private static readonly ReadOnlyCollection<Assembly> AllAssemblies = null;
        private static readonly ReadOnlyCollection<Assembly> BinFolderAssemblies = null;

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

            IList<Assembly> binFolderAssemblies = 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)
                {
                    binFolderAssemblies.Add(locatedAssembly);
                }
            }

            BinFolderAssemblies = new ReadOnlyCollection<Assembly> (binFolderAssemblies);
        }

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

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

You can use this in the IocControllerFactory like so:

public class IocControllerFactory : DefaultControllerFactory
{
    public IocControllerFactory()
    {
        Type controllerInterfaceType = typeof(IController);

        List<Type> controllerTypes = new List<Type>();

        foreach (Assembly assembly in AssemblyLocator.GetBinFolderAssemblies ())
        {
            // Rest of ControllerFactory class, see blog post (snip)

...or in the Bootstrapper class:

public class Bootstrapper
{
    static Bootstrapper()
    {
        Type bootStrapperType = typeof(IBootstrapperTask);

        List<Type> tasks = new List<Type>();

        foreach (Assembly assembly in AssemblyLocator.GetBinFolderAssemblies())
        {
            // Rest of Bootstrapper class, see blog post (snip)

How to get a Reference to all Assemblies in the \bin Folder

AppDomain.CurrentDomain.GetAssemblies() Considered Armed and Extremely Dangerous

Use BuildManager.GetReferencedAssemblies() Instead

2 Comments on "Assemblies in the \bin Folder"

RE: Assemblies in the \bin Folder

RE: RE: Assemblies in the \bin Folder

http://www.gucciitaly.net/

Thanks for writing.

http://www.monclersjackor.net

So we have a way to get a reference

RE: RE: RE: Assemblies in the \bin Folder

http://www.nikejordanfans.com

RE: RE: Assemblies in the \bin Folder

RE: RE: RE: Assemblies in the \bin Folder

http://www.cheapnikeshoxsneakers.com/

Franklin Marshall

max 95

RE: max 95

christian louboutin replica

RE: christian louboutin replica

RE: max 95

ugg boots sale

abercrombie and fitch

RE: RE: Assemblies in the \bin Folder

Jordan Retros

t shirt printing uk

ralph lauren polo

Leave a Comment

Random Image

Quick Poll

Latest Tweets