Assembly.CreateInstance returning null even though I can see the class in DefinedTypes

问题

I use the following method to load a new Assembly and create an instance of a class into a new AppDomain.

private static object CreateInstanceFromBinary(AppDomain appDomain, string typeName)
{
    Assembly entryAssembly = Assembly.GetEntryAssembly();

    byte[] assemblyBinary = LoadAssemblyBinary();

    Assembly loadedAssembly = appDomain.Load(assemblyBinary);
    if (loadedAssembly != null)
    {
        return loadedAssembly.CreateInstance(typeName);
    }

    return null;
}

Which get's called like so.

AppDomain appDomain = AppDomain.CreateDomain(domainName);

appDomainHelper = CreateInstanceFromBinary(appDomain, typeof(MyClass).FullName) as MyClass;

Looking into the loadedAssembly I can see that MyClass exists inside of the DefinedTypes and it's name matches typeName. However, when the code runs

loadedAssembly.CreateInstance(typeName)

it returns null.

This code was working, however, I recently moved this class into the same dll as the one that calls it and now it has started returning null.

Any ideas on how to fix this?

---

For some short(ish) reproducible code you can use the following. In this code ClassLibrary1 has CopyLocal set to false and then included as an EmbeddedResource to mimic what I have in my live project in case that matters.

Inside of ConsoleApplication1 I have Program.

using ClassLibrary1;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        static Program()
        {
            AppDomain.CurrentDomain.AssemblyResolve += Resolve;
        }

        static void Main(string[] args)
        {
            WorkerClass workerClass = new WorkerClass();
            workerClass.DoWork();

            Console.WriteLine("\r\nPress enter to exit...");
            Console.ReadLine();
        }

        static System.Reflection.Assembly Resolve(object sender, ResolveEventArgs args)
        {
            if (!args.Name.Contains(","))
            {
                return null;
            }

            List<string> rn = System.Reflection.Assembly.GetEntryAssembly().GetManifestResourceNames()
                                                                           .Where(r => r.EndsWith(".dll", StringComparison.OrdinalIgnoreCase))
                                                                           .ToList();

            string assemblyName = rn.FirstOrDefault(r => r.EndsWith(args.Name.Substring(0, args.Name.IndexOf(",")) + ".dll"));
            if (!String.IsNullOrEmpty(assemblyName))
            {
                using (Stream stream = System.Reflection.Assembly.GetEntryAssembly().GetManifestResourceStream(assemblyName))
                {
                    byte[] assemblyBinary = new byte[stream.Length];
                    stream.Read(assemblyBinary, 0, assemblyBinary.Length);

                    System.Reflection.Assembly assembly = System.Reflection.Assembly.Load(assemblyBinary);

                    if (Environment.UserInteractive)
                    {
                        Console.WriteLine("Loaded Assembly: " + assembly.FullName);
                    }

                    return assembly;
                }
            }

            if (Environment.UserInteractive)
            {
                Console.WriteLine($"** Failed to find an assembly with name: {args.Name} ** ");
            }

            return null;
        }
    }
}

Inside of ClassLibrary1 there is WorkerClass.

using System;

namespace ClassLibrary1
{
    public class WorkerClass
    {
        public void DoWork()
        {
            try
            {
                HelperClass hc = HelperClass.Create("Name");
                Console.WriteLine("Created");
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed to create: " + ex.ToString());
            }
        }
    }
}

and HelperClass.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Security.Permissions;

namespace ClassLibrary1
{
    [Serializable]
    public class HelperClass : MarshalByRefObject
    {
        public AppDomain Domain { get; private set; }

        public HelperClass()
        {

        }

        [SecurityPermission(SecurityAction.Demand, Flags = SecurityPermissionFlag.Infrastructure)]
        public override object InitializeLifetimeService()
        {
            return null;
        }

        public static HelperClass Create(string domainName)
        {
            AppDomain appDomain = AppDomain.CreateDomain(domainName);

            HelperClass helperClass = CreateInstanceFromBinary(appDomain, typeof(HelperClass).AssemblyQualifiedName) as HelperClass;
            if (helperClass == null)
            {
                throw new Exception("Unable to create instance from binary resource.");
            }

            helperClass.Domain = appDomain;

            return helperClass;
        }

        private static object CreateInstanceFromBinary(AppDomain appDomain, string typeName)
        {
            Assembly entryAssembly = Assembly.GetEntryAssembly();

            IList<string> rn = entryAssembly.GetManifestResourceNames().Where(r => r.EndsWith(".dll")).ToList();

            string assembly = rn.FirstOrDefault(r => r.EndsWith($"{typeof(HelperClass).Assembly.GetName().Name}.dll"));
            if (!String.IsNullOrEmpty(assembly))
            {
                using (Stream stream = entryAssembly.GetManifestResourceStream(assembly))
                {
                    byte[] assemblyBinary = new byte[stream.Length];
                    stream.Read(assemblyBinary, 0, assemblyBinary.Length);

                    Assembly loadedAssembly = appDomain.Load(assemblyBinary);
                    if (loadedAssembly != null)
                    {
                        return loadedAssembly.CreateInstance(typeName);
                    }
                }
            }

            return null;
        }
    }
}

Where it is return loadedAssembly.CreateInstance(typeName); that returns null.

回答1:

In your function public static HelperClass Create(string domainName) you are passing the AssemblyQualifiedName as the type of the class to create.

I think you just want to pass the type name, ie: ClassLibrary1.HelperClass

//HelperClass helperClass = CreateInstanceFromBinary(appDomain, typeof(HelperClass).AssemblyQualifiedName) as HelperClass;
HelperClass helperClass = CreateInstanceFromBinary(appDomain, typeof(HelperClass).ToString()) as HelperClass;

I tried some variations, each time passing in the Assembly Qualified Name failed, just the type name worked as expected.

Variations tried, and failed:

 // Do not work
 var x = loadedAssembly.CreateInstance(typeName); //AssemblyQualifiedName
 var loadedType = loadedAssembly.GetType(typeName); //AssemblyQualifiedName

 // Work
 var x = Activator.CreateInstance(typeof(HelperClass)); // Works
 var x = loadedAssembly.CreateInstance("ClassLibrary1.HelperClass");

 var loadedType = loadedAssembly.GetType("ClassLibrary1.HelperClass");
 var x = Activator.CreateInstance(loadedType);

来源：https://stackoverflow.com/questions/49488782/assembly-createinstance-returning-null-even-though-i-can-see-the-class-in-define