Question

using System;
using System.IO;
using System.Reflection;
using System.Text;
using MyApp.Logging;

namespace MyApp.SmsService.Common
{
    public class MyAppAppDomain:MarshalByRefObject
    {
        private readonly AppDomainSetup domaininfo;
        private readonly AppDomain appDomain;
        public static string libDllPath;

        public MyAppAppDomain(string appDomainName) //Constructor
        {
            //Setup the App Domain Parameters
            domaininfo = new AppDomainSetup();
            domaininfo.ApplicationBase = AppDomain.CurrentDomain.SetupInformation.ApplicationBase;
            domaininfo.DisallowBindingRedirects = false;
            domaininfo.DisallowCodeDownload = true;
            domaininfo.ConfigurationFile = AppDomain.CurrentDomain.SetupInformation.ConfigurationFile;

            // Create the application domain.
            appDomain = AppDomain.CreateDomain(appDomainName, null, domaininfo);

            //Set the dll path using Static class ref.

            //Dependency resolution handler
            appDomain.AssemblyResolve += LoadFromLibFolder; /*Exception*/
        }

        private static Assembly LoadFromLibFolder(object sender, ResolveEventArgs args)
        {

            if (libDllPath != null)
            {
                string assemblyPath = Path.Combine(libDllPath, new AssemblyName(args.Name).Name + ".dll");

                if (File.Exists(assemblyPath) == false)
                {
                    return null;
                }
                Assembly assembly = Assembly.LoadFrom(assemblyPath);
                //Assembly dependancy resolved.

                return assembly;
            }

            return null;
        }

        public Object getNewInstanceOf(string fullyQualifiedTypeName)
        {
            return appDomain.CreateInstanceAndUnwrap(Assembly.GetExecutingAssembly().FullName, fullyQualifiedTypeName);
        }

        public Type getTypeOf(string fullyQualifiedTypeName)
        {
            return getNewInstanceOf(fullyQualifiedTypeName).GetType();
        }

        public void unloadDomain()
        {
            AppDomain.Unload(appDomain);
        }
    }
}

The above class is a wrapper that I want to create to setup and teardown an application domain. However, in my webservice I am getting a FileNotFoundException [Failed to load a dll xyz.dll] whenever I am instantiating the object of MyAppAppDomain.

Following is the ex:

MyAppAppDomain.libDllPath = appDllLibPath; //Some directory other than bin.
pluginDomain = new MyAppAppDomain("SmsServicePlugins"); //Throws FileNotFoundException.

When I debug, I see that the line that caused the exception is the one marked above as /exception/, inside the constructor of MyAppAppDomain.

What is going wrong?

EDIT:

I was going through other articles and I read that objects cannot be visible across domains. This can only happen when the object can be serialized in both domains (use of MarshalByRefObject) and then can be accessed through proxies.

Would be of great help if someone can point out the issues in the above code. In the meanwhile I am attempting to learn more on Marshalling and Proxy-ing.

Answer 1

First problem is you are trying to doing everything inside app domain wrapper, it is really two different components. The first component you need is your object that you want to create inside your new app domain which inherits from MarshalByRefObject (or marked as Serializable). The other lives inside your current AppDomain and is used to create the new AppDomain.

Have a look at the msdn example to see what I mean.

However your error is probably more than likely that your path is wrong to your DLL. Could you show the full stack trace to show what line is throwing the exception?