How to load a .NET assembly for reflection operations and subsequently unload it?

Question

I\'m writing a tool to report information about .NET applications deployed across environments and regions within my client\'s systems.

I\'d like to read the values

Answer 1

You can try to use Unmanaged Metadata API, which is COM and can easily be used from .NET application with some kind of wrapper.

Answer 2

Whilst not really about unloading assemblies, if you're just trying to get the version number of a file you can use System.Diagnostics.FileVersionInfo.

var info = FileVersionInfo.GetVersionInfo(path);

FileVersionInfo has the following properties:

public string Comments { get; }
public string CompanyName { get; }
public int FileBuildPart { get; }
public string FileDescription { get; }
public int FileMajorPart { get; }
public int FileMinorPart { get; }
public string FileName { get; }
public int FilePrivatePart { get; }
public string FileVersion { get; }
public string InternalName { get; }
public bool IsDebug { get; }
public bool IsPatched { get; }
public bool IsPreRelease { get; }
public bool IsPrivateBuild { get; }
public bool IsSpecialBuild { get; }
public string Language { get; }
public string LegalCopyright { get; }
public string LegalTrademarks { get; }
public string OriginalFilename { get; }
public string PrivateBuild { get; }
public int ProductBuildPart { get; }
public int ProductMajorPart { get; }
public int ProductMinorPart { get; }
public string ProductName { get; }
public int ProductPrivatePart { get; }
public string ProductVersion { get; }
public string SpecialBuild { get; }

Answer 3

You can create an instance in the new AppDomain and execute your code in that instance.

var settings = new AppDomainSetup
{
    ApplicationBase = AppDomain.CurrentDomain.BaseDirectory,
};
var childDomain = AppDomain.CreateDomain(Guid.NewGuid().ToString(), null, settings);

 var handle = Activator.CreateInstance(childDomain,
            typeof(ReferenceLoader).Assembly.FullName,
            typeof(ReferenceLoader).FullName,
            false, BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance, null, null, CultureInfo.CurrentCulture, new object[0]);


var loader = (ReferenceLoader)handle.Unwrap();

//This operation is executed in the new AppDomain
var paths = loader.LoadReferences(assemblyPath);


AppDomain.Unload(childDomain);

Here is the ReferenceLoader

public class ReferenceLoader : MarshalByRefObject
{
    public string[] LoadReferences(string assemblyPath)
    {
        var assembly = Assembly.ReflectionOnlyLoadFrom(assemblyPath);
        var paths = assembly.GetReferencedAssemblies().Select(x => x.FullName).ToArray();
        return paths;
    }
}

Answer 4

You have to use application domains, there's no other way to unload an assembly. Basically you have to use code like this:

AppDomain tempDomain = AppDomain.CreateDomain("Temp Domain");
tempDomain.Load(assembly);
AppDomain.Unload(tempDomain);

Answer 5

From the MSDN documentation of System.Reflection.Assembly.ReflectionOnlyLoad (String) :

The reflection-only context is no different from other contexts. Assemblies that are loaded into the context can be unloaded only by unloading the application domain.

So, I am afraid the only way to unload an assembly is unloading the application domain. To create a new AppDomain and load assemblies into it:

public void TempLoadAssembly()
{
    AppDomain tempDomain = AppDomain.CreateDomain("TemporaryAppDomain");
    tempDomain.DoCallBack(LoaderCallback);
    AppDomain.Unload(tempDomain);
}

private void LoaderCallback()
{
    Assembly.ReflectionOnlyLoad("YourAssembly");
    // Do your stuff here
}