如何在.net核心控制台应用程序的文件夹中加载程序集 [英] How to load assemblies located in a folder in .net core console app

问题描述

我正在.Net Core平台上制作一个控制台应用程序，并且想知道，如何使用C＃动态功能加载程序集（.dll文件）并实例化类？它似乎与.Net 4.X有很大不同，并且没有真正记录在文档中。

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...

例如，假设我有一个类库（.Net Core），它仅具有一个类：

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;
        }
    }
}

因此dll的名称文件将是 MyClassLib.dll ，位于 /dlls/MyClassLib.dll 中。

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

现在，我想将其加载到简单的控制台应用程序（.Net Core）中，并实例化 Sample 类，并使用的动态功能调用方法以下控制台应用中的C＃：

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
        }
    }
}

注意：
.Net Core我的意思是RC2版本。

Note: By .Net Core I mean RC2 version.

推荐答案

不确定这是否是最好的方法，但这是我想出的：

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

（仅在.Net Core RC2-Windows上测试）

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 是命名空间，而 Sample 是类型名。

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

执行后，它将尝试将 SampleClassLib.dll 编译的类库加载到内存中，并使控制台应用程序可以访问 MyClassLib .SampleClasses.Sample （看看问题），然后我的应用程序调用方法 SayHello（）并将 John Doe作为名称传递给它，因此该程序将打印：

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:

你好，约翰·道伊

快速说明：
方法 Load 的覆盖无关紧要您最好将其内容替换为并抛出新的NotImplementedException（），它不应影响我们所关心的任何事情。

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.

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