如何加载位于 .NET Core 控制台应用程序文件夹中的程序集 [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，想知道如何使用 C# 动态功能加载程序集(.dll 文件)和实例化类?它似乎与 .NET 4.X 大不相同，并且没有真正记录在案...

I'm making a console app on the .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) 并且它只有一个类:

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;
        }
    }
}

所以 dll 文件的名称将是 MyClassLib.dll，它位于 /dlls/MyClassLib.dll.

So the name of the dll file would be MyClassLib.dll and it's located in /dlls/MyClassLib.dll.

现在我想在一个简单的控制台应用程序 (.NET Core) 中加载它并实例化 Sample 类并在以下控制台应用程序中使用 C# 的动态特性调用方法:

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 是指 RC2 版本.

Note: By .NET Core, I mean the RC2 version.

推荐答案

不确定这是否是最好的方法，但我想到了:

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:LocationOf" + "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，Sample 是类型，也就是类名.

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

执行时，它会尝试在内存中加载 SampleClassLib.dll 编译的类库，并让我的控制台应用程序访问 MyClassLib.SampleClasses.Sample(取一个看问题)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，因此程序打印:

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:

Hello John Doe"

快速说明:方法 Load 的覆盖无关紧要，因此您不妨将其内容替换为 throw new NotImplementedException() 并且它不应该影响我们关心的任何事情.

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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