CODEWITHSUNDEEP
c#.netreflection
Dan Hass
Dan Hass

Reputation: 67

Unable to load one or more of the requested types. retrieve the loaderexceptions

I've made up a small test app to demo the issue I'm trying to resolve. I have a plugin architecture where the plugins derive from an interface.

Here's is the interface code:

namespace Test
{
  public interface ITestBase
  {
    int LifeTheUniverseAndEverything();
    bool Pessimist();
    bool Optimist();
  }
}

This builds to a .dll that is referenced by the main program solution and the plugin solution.

Here is the plugin code:

namespace Test
{
  public class TestPlugin : ITestBase
  {
    public int LifeTheUniverseAndEverything() { return 41; }
    public bool Pessimist() { return false; }
    public bool Optimist() { return true; }
  }
}

This produces a .dll that is dropped into a "plugins" folder off the main working directory.

Here's the main program.

namespace Test
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("testing...");
      string[] PluginFileLocs;
      try
      {
        string sWorkingDir = Directory.GetCurrentDirectory();
        string sPluginDir = sWorkingDir + "\\Plugins";
        PluginFileLocs = Directory.GetFiles(sPluginDir, "*.dll");
        foreach (string plugin in PluginFileLocs)
        {
          Assembly theAssembly = Assembly.ReflectionOnlyLoadFrom(plugin);
          foreach (Type type in theAssembly.GetTypes())
          {
            string aType = type.FullName;
            Console.WriteLine(aType);
          }
        }
      }
      catch (Exception e)
      {
        Console.WriteLine("Error: " + e.Message);
      }
    }
  }
}

The issue is, that if the testplugin class derives off the ITestBase interface, the theAssembly.GetTypes throws an exception: unable to load one or more of the requested types. retrieve the LoaderExceptions. Why, and how can I get my plugin to derive off an interface?

Upvotes: 1

Views: 4494

Answers (2)

vcsjones
vcsjones

Reputation: 141688

Without further detail, it's hard to tell. My guess would be because you are loading it into a Reflection Only context by using ReflectionOnlyLoadFrom, which won't resolve dependencies, and the interface and plug ins are in different assemblies, you need to handle the ReflectionOnlyAssemblyResolve on the AppDomain, or don't load it in a reflection-only context.

Since you are likely to actually load your plug-in and execute them, it may be simplier to just load it completely. Best practice for plug ins is to load them in a different AppDomain and lock it down to keep the plug-in in a sandbox.

Upvotes: 1

Tony
Tony

Reputation: 684

Based on the documentation for the Assembly.ReflectionOnlyLoadFrom, it will not automatically load dependencies http://msdn.microsoft.com/en-us/library/system.reflection.assembly.reflectiononlyloadfrom.aspx

I'm guessing that's what's going on here. Since your interface is defined in a separate assembly from the plugin, you must first load that assembly before trying to call GetTypes.

Upvotes: 3

Related Questions