VSG24 VSG24 - 4 months ago 44
C# Question

How to load assemblies located in a folder in .net core console app

I'm making a console app on .Net Core platform and was wondering, how does one load assemblies (.dll files) and instantiate classes using C# dynamic features? It seems so much different than .Net 4.X and it's not really documented...

For example let's say I have a class library (.Net Core) and it has only one class:

namespace MyClassLib.SampleClasses
{
public class Sample
{
public string SayHello(string name)
{
return $"Hello {name}";
}

public DateTime SayDateTime()
{
return DateTime.Now;
}
}
}


So the name of the dll file would be
MyClassLib.dll
and its located in
/dlls/MyClassLib.dll
.

Now I want to load this in a simple console app (.Net Core) and instantiate the
Sample
class and call the methods using dynamic features of C# in the following console app:

namespace AssemblyLoadingDynamic
{
public class Program
{
public static void Main(string[] args)
{
// load the assembly and use the classes
}
}
}


Note:
By .Net Core I mean RC2 version.

Answer

Not sure if it's the best way to do it but here's what I came up with:

(Only tested on .Net Core RC2 - Windows)

using System;
using System.Linq;
using System.Reflection;
using System.Runtime.Loader;
using Microsoft.Extensions.DependencyModel;

namespace AssemblyLoadingDynamic
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var asl = new AssemblyLoader();
            var asm = asl.LoadFromAssemblyPath(@"C:\Location\Of\" + "SampleClassLib.dll");

            var type = asm.GetType("MyClassLib.SampleClasses.Sample");
            dynamic obj = Activator.CreateInstance(type);
            Console.WriteLine(obj.SayHello("John Doe"));
        }

        public class AssemblyLoader : AssemblyLoadContext
        {
            // Not exactly sure about this
            protected override Assembly Load(AssemblyName assemblyName)
            {
                var deps = DependencyContext.Default;
                var res = deps.CompileLibraries.Where(d => d.Name.Contains(assemblyName.Name)).ToList();
                var assembly = Assembly.Load(new AssemblyName(res.First().Name));
                return assembly;
            }
        }
    }
}

MyClassLib.SampleClasses is the namespace and Sample is the type aka class name.

When executed, it will try to load the SampleClassLib.dll compiled class library in the memory and gives my console app access to MyClassLib.SampleClasses.Sample (take a look at the question) then my app calls the method SayHello() and passes "John Doe" as name to it, Therefore the program prints:

"Hello John Doe"

Quick note: The override for the method Load doesn't matter so you might as well just replace its content with throw new NotImplementedException() and it shouldn't affect anything we care about.