“Could not load file or assembly 'System.Core, Version=2.0.5.0,…” exception when loading Portable Class Library dynamically

问题

First of all I need to emphasize that this is slightly different question than the one in this thread. Additionally, installing KB2468871 doesn't help.

I tried to simplify this problem as much as possible. In general it about loading PCL assemblies in Desktop application with Assembly.LoadFile(...).

Let's say there is a .NET 4.0 Console Application (called "C"). It references .NET 4.0 assembly (called "N4") and PCL assembly (called "PCL").

where N4 looks like this:

using System.Linq;

namespace N4
{
    public class ClassInN4
    {
        public static string Greet()
        {
            return new string(
                "hello from N4"
                .ToCharArray()
                .Select(char.ToUpper)
                .ToArray()
            );
        }
    }
}

PCL looks like this:

using System.Linq;

namespace PCL
{
    public class ClassInPCL
    {
        public static string Greet()
        {
            return new string(
                "hello from pcl"
                .ToCharArray()
                .Select(char.ToUpper)
                .ToArray()
            );
        }
    }
}

and C look like this:

using System;
using System.IO;
using System.Reflection;
using N4;
using PCL;

namespace C
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            Test();
            Console.ReadLine();
        }

        private static void Test()
        {
            Test("N4", ClassInN4.Greet);
            Test("PCL", ClassInPCL.Greet);
        }

        private static void Test(
            string title, 
            Func<string> generator)
        {
            try
            {
                Console.WriteLine(
                    "{0}: {1}", title, generator());
            }
            catch (Exception e)
            {
                Console.WriteLine(
                    "{0}: {1} -> {2}", title, e.GetType(), e.Message);
            }
        }
    }
}

When you run this application you get absolutely correct results:

N4: HELLO FROM N4
PCL: HELLO FROM PCL

Let's add AssemblyResolve event to CurrentDomain in Program.Main:

AppDomain.CurrentDomain.AssemblyResolve += (_, a) => {
    var fileName = Path.GetFullPath(
        new AssemblyName(a.Name).Name + ".data");
    Console.WriteLine("Probing '{0}'", fileName);
    return 
        File.Exists(fileName) 
        ? Assembly.LoadFile(fileName) 
        : null;
};

So, what it does if assembly cannot be found it tries to load it from ".data" file.

Let's go application folder and rename "N4.dll" to "N4.data" and run "C.exe".

Probing 'C:\xxx\C\bin\Debug\N4.data'
N4: HELLO FROM N4
PCL: HELLO FROM PCL

So it goes through AssemblyResolve and finally loads "N4.data" and works as good as original.

Let's revert "N4.data" to "N4.dll" and rename "PCL.dll" to "PCL.data" and...

Probing 'C:\xxx\C\bin\Debug\PCL.data'
N4: HELLO FROM N4
Probing 'C:\xxx\C\bin\Debug\System.Core.data'
Probing 'C:\xxx\C\bin\Debug\System.Core.data'
Probing 'C:\xxx\C\bin\Debug\System.Core.data'
PCL: System.IO.FileNotFoundException -> Could not load file or assembly 'System.Core, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes' or one of its dependencies. The system cannot find the file specified.

Please note that PCL assembly was loaded just fine, the problem is, it only can't find its dependencies (System.Core) anymore.

It's like Assembly.LoadFile(fileName) is-a no-no if loaded assembly is portable.

Did anyone have this problem? Did anyone solved this problem?

You can find all files here.

EDIT: Thanks to leppie for forcing me to check other options. I actually wanted to be sure that I'm not lying while I answer "Yeah, yeah, I tried". Apparently it was worth checking.

From Suzanne Cook's .NET CLR Notes:

Be careful - these aren't the same thing.

LoadFrom() goes through Fusion and can be redirected to another assembly at a different path but with that same identity if one is already loaded in the LoadFrom context. LoadFile() doesn't bind through Fusion at all - the loader just goes ahead and loads exactly* what the caller requested. It doesn't use either the Load or the LoadFrom context.

回答1:

You can return the System.Core assembly of your platform (e.g. version 4.0.0.0 for .NET Framework 4.0) from the AssemblyResolve event, when asked for the 2.0.5.0 version.

I am loading all my referenced assemblies stored as resources via Load(byte[]), which also fails to resolve the 2.0.5.0 assembly, and I retrieve both System and System.Core from AppDomain.CurrentDomain.GetAssemblies().

回答2:

I think you are getting these issues because:

You're getting an exception because you haven't got the latest .NET updates.

http://www.paraesthesia.com/archive/2013/01/21/using-portable-class-libraries-update-net-framework.aspx

Take note of the WSUS part - you may think you have the latest updates, but you don't cause your WSUS server is out of date.

This patch may help, but you're better just to get all the .net updates:

http://support.microsoft.com/kb/2468871

(from a comment above)

Try LoadFrom(...) rather than LoadFile(...) / Load(byte[]) and see if that fixes your issue? :)

回答3:

I had the same problem and ended up with the following solution: invoke the following code before dynamically loading the PCL assembly.

Assembly.Load("System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes");
Assembly.Load("System.Core, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes");

If any other dependency is missing when you load your PCL assembly, you just need to add a line to code above. For some strange and ununderstandable reason, it works.

来源：https://stackoverflow.com/questions/18277499/could-not-load-file-or-assembly-system-core-version-2-0-5-0-exception-wh

标签

.net

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