Loading interdependent assemblies from C++/CLI

Question

I want to load two assemblies from C++/CLI; assembly A depends on assembly B, and both are VB.Net projects (3.5). I want them to load from a byte array, so I use Assembly::Load(), but when I try to instantiate a class from assembly A, the framework ignores the previously loaded assembly B and attempts to load it again, which fails because it is not in the search path. The "Name" of the assembly is the same, so I don't know why it fails. For testing purposes, my program loads the bytes directly from the compiled image, but the real code will be loaded differently. This is my test code:

#include "stdafx.h"

using namespace System;
using namespace System::Windows::Forms;
using namespace System::IO;
using namespace System::Reflection;

[STAThreadAttribute]
int main(array<System::String ^> ^args)
{
    array<unsigned char>^   bytes;
    FileStream^     f;

    f = gcnew FileStream(L"c:\\...\\AssemblyB.dll", FileMode::Open);
    bytes = gcnew array<unsigned char>((int)f->Length);
    f->Read( bytes, 0, (int) f->Length );
    f->Close();
    f = nullptr;
    Assembly^   assemblyb = Assembly::Load(bytes);

    f = gcnew FileStream(L"c:\\...\\AssemblyA.dll", FileMode::Open);
    bytes = gcnew array<unsigned char>((int)f->Length);
    f->Read( bytes, 0, (int) f->Length );
    f->Close();
    f = nullptr;
    Assembly^   assemblya = Assembly::Load(bytes);

    bytes = nullptr;

    // Here I get the file not found exception!
    Object^     mf = assemblya->CreateInstance(L"AssemblyA.MainForm");

    // This line is not reached unless I copy assemblyb.dll to my app's folder:
    mf->GetType()->InvokeMember(L"ShowDialog",BindingFlags::Default | BindingFlags::InvokeMethod,
                                mf->GetType()->DefaultBinder, mf, nullptr );

    return 0;
}

The error is:

Could not load file or assembly 'AssemblyB, Version=1.0.3650.39903, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

When I check assemblyb->FullName, it says exactly 'AssemblyB, Version=1.0.3650.39903, Culture=neutral, PublicKeyToken=null'.

Of course, if I copy AssemblyB.dll to my test program's folder the code works just fine, but that's not what I want.

Any ideas?

(By the way, my second step will be attempt to make AssemblyA use classes that my C++/CLI exe will expose.)

Mmmm... from what I read here (http://stackoverflow.com/questions/416468/weird-behaviour-when-mixing-loading-of-assemblies-using-assembly-loadfrom-and-ass) it seems I should be implementing a ResolveHandler, but I don't have the faintest idea of what's the syntax for AddHandler() in C++/CLI! :P — Guillermo Prandi, Dec 30 '09 at 02:14

score 9 · Accepted Answer · answered Dec 30 '09 at 02:39

OK, I just embarrased myself. It's all in the docs.

// This class is just for holding a managed static variable for assemblyB
ref class Resolver {
public:
    static  Assembly^   assemblyB;
};

// This is the delegate for resolving assemblies
Assembly^ ResolveHandler(Object^ Sender, ResolveEventArgs^ args)
{
    // Warning: this should check the args for the assembly name!
    return Resolver::assemblyB;
}
.
.
.
[STAThreadAttribute]
int main(array<System::String ^> ^args)
{
    // Set up the handler for the AssemblyResolve event
    AppDomain::CurrentDomain->AssemblyResolve += gcnew ResolveEventHandler( ResolveHandler );
.
.
.
    // Load assemblyb into the static variable available to the resolver delegate
    Resolver::assemblyb = Assembly::Load(bytes);
.
.
.

I hope someone finds this useful. :)

Loading interdependent assemblies from C++/CLI

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