在C＃MVC中使用MEF，程序集正在加载一些DLL，如何卸载它们？

Question

Sorry in advance I'm not sure if I've phrased the question correctly, here's my situation... Using .NET 4.6 with MEF.

I have a core website that, at run time, checks a modules folder for DLLs and pulls them into a Composition Container / MEF thing, which lets me use the views/controllers of the 3rd party project, in my core.

To allow strong typing, I followed this guide which suggests making a shadow copy of the DLLs in a PreApplicationStartMethod.

All working so far, really great.

The problem comes when I stop debugging or when the server recompiles. The DLLs are not being released properly, so I get access denied errors 2nd time around. The error happens when I try to copy DLLs into the shadow copy folder.

The process cannot access the file '....dll' because it is being used by another process.

I guess it's the BuildManager.AddReferencedAssembly(assemblyDll) which is locking the file in... but is there a reliable way to unload the assembly either on crash or on start up?

static PreApplicationInit()
    {
        PluginFolder = new DirectoryInfo(HostingEnvironment.MapPath("~/Modules"));
        ShadowCopyFolder = new DirectoryInfo(HostingEnvironment.MapPath("~/Modules/temp"));
    }
public static void Initialize()
    {
        Directory.CreateDirectory(ShadowCopyFolder.FullName);

        //clear out plugins)
        foreach (var f in ShadowCopyFolder.GetFiles("*.dll", SearchOption.AllDirectories))
        {
            f.Delete(); // -- Breaks here
        }

        //shadow copy files
        foreach (var plug in PluginFolder.GetFiles("*.dll", SearchOption.AllDirectories))
        {
            var di = Directory.CreateDirectory(Path.Combine(ShadowCopyFolder.FullName, plug.Directory.Name));
            File.Copy(plug.FullName, Path.Combine(di.FullName, plug.Name), true); // -- Or if Delete is Try Caught, Breaks here
        }

        foreach (var a in
            ShadowCopyFolder
            .GetFiles("*.dll", SearchOption.AllDirectories)
            .Select(x => AssemblyName.GetAssemblyName(x.FullName))
            .Select(x => Assembly.Load(x.FullName)))
        {
            BuildManager.AddReferencedAssembly(a);
        }

    }

Answer 1

There can be many possible reasons but the main reason for this i think is, when you recompile some of the dll from your previous compile are still in process and it wont let you have access until the entire process is finished (which in a term it will have a lock). if you want to recompile try changing the folder. it should work.