C＃动态加载/卸载DLL Redux（当然使用AppDomain）

Question

我已经阅读了Stack Overflow上这个问题的不同版本，以及3个不同Google搜索教程的首页上的每个蓝色链接，以及MSDN（这是一种浅薄的执行程序集）。我只能想到我努力让Tao作为一个好的测试用例，但请相信我，我尝试过一个简单的字符串返回，一个double，一个带参数的函数。无论我的问题是什么，都不是道。

基本上我想在GLPlugin命名空间中创建一个我的Draw类的testLibraryDomain.CreateInstance()。

        if( usePlugin )
        {
                AppDomain testLibraryDomain = AppDomain.CreateDomain( "TestGLDomain2" );

                //What the heck goes here so that I can simply call
                //the default constructor and maybe a function or two?

                AppDomain.Unload( testLibraryDomain );
        }
        Gl.glBegin( Gl.GL_TRIANGLES );

我知道一个事实：

namespace GLPlugin
{
    public class DrawingControl : MarshalByRefObject
    {
        public DrawingControl()
        {
            Gl.glColor3f( 1.0f , 0.0f , 0.0f );

            //this is a test to make sure it passes
            //to the GL Rendering context... success
        }
    }
}

确实改变了笔的颜色。当我给它一个static void Main( string args[] )入口点并且我调用testLibraryDomain.ExecuteAssembly( thePluginFilePath )时它是否正常工作是否直接的ExecuteAssembly会起作用关注我，因为我不确定GL调用是否会使它进入“顶级” “AppDomain的OpenGL上下文。它甚至可以让我覆盖组件并再次更换笔颜色。不幸的是，给它一个可执行的入口点意味着弹出控制台会打断我然后消失。它也适用于我只是在项目中给它一个引用并创建一个常规GLPlugin.DrawingTool tool = new GLPlugin.DrawingControl()，甚至创建一个someAssembly = Assembly.LoadFrom( thePluginFilePath )（当然，不幸的是，锁定程序集，阻止替换/重新编译）。 / p>

当使用我尝试的各种方法时，我总是得到“给定的程序集名称或其代码库无效”。我保证，这是有效的。我试图加载它的方式不是。

我知道我缺少的一件事是testLibraryDomain.CreateInstance( string assemblyName , string typeName);

的正确设置

据我所知，assemblyName参数不是程序集文件的文件路径。它是名称空间，还是只是程序集名称，即：GLPlugin？如果是这样，我在哪里引用实际文件？没有someAppDomain.LoadFrom（someFilename），虽然如果有的话会很方便。另外，什么是Type，以及字符串typeName呢？我不想把"Object"放在这里，因为除了对象的实例之外不创建类型吗？我也试过CreateInstanceAndUnwrap( ... , ... )同样缺乏对AppDomain的基本理解。通常我可以混淆教程并让事情发挥作用，即使我经常不理解“为什么？”......在这里不是这样。通常，对我来说，查找六个不同的教程是有帮助的......在这里不再如此，但因为每个教程都采用了一种基本的（或似乎是这样的）方法。

请ELI5 ...我想在一个单独的AppDomain中从一个dll加载一个类的实例，可能运行一些函数，然后卸载它。最终创建一个列表，列出这些函数作为List，删除/更新必要......我也希望能够将参数传递给它们，但这将是第2步。根据StackOverflow，我必须了解{ {1}}我将推迟一天。 （我想你可以从我的例子中找出我想要做的事情。）

Answer 1

好的，我们必须澄清一些事情。首先，如果您希望能够在不锁定文件iteslf的情况下将dll加载和卸载到不同的AppDomain，也许您可​​以使用这样的方法：

AppDomain apd = AppDomain.CreateDomain("newdomain");
using(var fs = new FileStream("myDll.dll", FileMode.Open))
{
    var bytes = new byte[fs.Length];
    fs.Read(bytes, 0, bytes .Length);
    Assembly loadedAssembly = apd.Load(bytes);
} 

这样，您就不会锁定该文件，您应该可以稍后卸载域，重新编译该文件并在以后使用较新版本加载它。但我不能100％确定这是否会破坏您的申请。

那是因为第二件事。如果您将使用CreateInstanceAndUnwrap方法，根据MSDN，您必须在两个appdomains中加载程序集 - 正在调用的程序集和您正在调用的程序集。当您在AppDomains中加载两个不同的dll时，这可能会在某种情况下结束。

The assembly that contains unwrapped class must be loaded into both application domains, but it can load other assemblies that exist only in the new application domain.

我现在不记得了，但我认为当你打电话给CreateInstanceAndUnwrap时，两个应用领域中对象创建的行为会有所不同，但我不记得细节。

对于您的插件架构，您可能需要阅读此博文。 About how to handle Dynamic Plugins using the AppDomain Class to Load and Unload Code

修改

我忘记了这个AppDomains是如何工作的，我可能会引入一些混乱。我准备了“插件”架构如何工作的简短示例。它与我之前提到的博客中描述的内容非常相似，这里是我使用Shadow Copying的示例。如果由于某些原因您不想使用它，可以很容易地更改为使用AppDomain.Load(byte[] bytes)

我们有3个程序集，第一个是基本插件程序集，它将作为代理使用，并将加载到所有AppDomains（在我们的例子中 - 在主应用程序域和插件应用程序域中）。

namespace PluginBaseLib
{
    //Base class for plugins. It has to be delivered from MarshalByRefObject,
    //cause we will want to get it's proxy in our main domain. 
    public abstract class MyPluginBase : MarshalByRefObject 
    {
        protected MyPluginBase ()
        { }

        public abstract void DrawingControl();
    }

    //Helper class which instance will exist in destination AppDomain, and which 
    //TransparentProxy object will be used in home AppDomain
    public class MyPluginFactory : MarshalByRefObject
    {
        //This method will be executed in destination AppDomain and proxy object
        //will be returned to home AppDomain.
        public MyPluginBase CreatePlugin(string assembly, string typeName)
        {
            Console.WriteLine("Current domain: {0}", AppDomain.CurrentDomain.FriendlyName);
            return (MyPluginBase) Activator.CreateInstance(assembly, typeName).Unwrap();
        }
    }

    //Small helper class which will show how to call method in another AppDomain. 
    //But it can be easly deleted. 
    public class MyPluginsHelper
    {
        public static void LoadMyPlugins()
        {
            Console.WriteLine("----------------------");
            Console.WriteLine("Loading plugins in following app domain: {0}", AppDomain.CurrentDomain.FriendlyName);
            AppDomain.CurrentDomain.Load("SamplePlugin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null");
            Console.WriteLine("----------------------");
        }
    }
}

这里我们将有另一个带有我们的虚拟插件的程序集，名为SamplePlugin.dll，存储在“Plugins”文件夹下。它引用了PluginBaseLib.dll

namespace SamplePlugin
{
    public class MySamplePlugin : MyPluginBase
    {
        public MySamplePlugin()
        { }

        public override void DrawingControl()
        {
            var color = Console.ForegroundColor;
            Console.ForegroundColor = ConsoleColor.Green;
            Console.WriteLine("----------------------");
            Console.WriteLine("This was called from app domian {0}", AppDomain.CurrentDomain.FriendlyName );
            Console.WriteLine("I have following assamblies loaded:");
            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
            {
                Console.WriteLine("\t{0}", assembly.GetName().Name);
            }
            Console.WriteLine("----------------------");
            Console.ForegroundColor = color;
        }
    }
}

最后一个程序集（简单的控制台应用程序），它只引用PluginBaseLib.dll和

namespace ConsoleApplication1
{
    //'Default implementation' which doesn't use any plugins. In this sample 
    //it just lists the assemblies loaded in AppDomain and AppDomain name itself.
    public static void DrawControlsDefault()
    {
        Console.WriteLine("----------------------");
        Console.WriteLine("No custom plugin, default app domain {0}", AppDomain.CurrentDomain.FriendlyName);
        Console.WriteLine("I have following assamblies loaded:");
        foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
        {
            Console.WriteLine("\t{0}", assembly.GetName().Name);
        }
        Console.WriteLine("----------------------");
    }

    class Program
    {
        static void Main(string[] args)
        {
            //Showing that we don't have any additional plugins loaded in app domain. 
            DrawControlsDefault();

            var appDir = AppDomain.CurrentDomain.BaseDirectory;
            //We have to create AppDomain setup for shadow copying 
            var appDomainSetup = new AppDomainSetup
                                 {
                                     ApplicationName = "", //with MSDN: If the ApplicationName property is not set, the CachePath property is ignored and the download cache is used. No exception is thrown.
                                     ShadowCopyFiles = "true",//Enabling ShadowCopy - yes, it's string value
                                     ApplicationBase = Path.Combine(appDir,"Plugins"),//Base path for new app domain - our plugins folder
                                     CachePath = "VSSCache"//Path, where we want to have our copied dlls store. 
                                 };
        var apd = AppDomain.CreateDomain("My new app domain", null, appDomainSetup);

        //Loading dlls in new appdomain - when using shadow copying it can be skipped,
        //in CreatePlugin method all required assemblies will be loaded internaly,  
        //Im using this just to show how method can be called in another app domain. 
        //but it has it limits - method cannot return any values and take any parameters.

        //apd.DoCallBack(new CrossAppDomainDelegate(MyPluginsHelper.LoadMyPlugins));

        //We are creating our plugin proxy/factory which will exist in another app domain 
        //and will create for us objects and return their remote 'copies'. 
        var proxy = (MyPluginFactory) apd.CreateInstance("PluginBaseLib", "PluginBaseLib.MyPluginFactory").Unwrap();

        //if we would use here method (MyPluginBase) apd.CreateInstance("SamplePlugin", "SamplePlugin.MySamplePlugin").Unwrap();
        //we would have to load "SamplePlugin.dll" into our app domain. We may not want that, to not waste memory for example
        //with loading endless number of types.
        var instance = proxy.CreatePlugin("SamplePlugin", "SamplePlugin.MySamplePlugin");
        instance.DrawingControl();

        Console.WriteLine("Now we can recompile our SamplePlugin dll, replace it in Plugin directory and load in another AppDomain. Click Enter when you ready");
        Console.ReadKey();

        var apd2 = AppDomain.CreateDomain("My second domain", null, appDomainSetup);
        var proxy2 = (MyPluginFactory)apd2.CreateInstance("PluginBaseLib", "PluginBaseLib.MyPluginFactory").Unwrap();
        var instance2 = proxy2.CreatePlugin("SamplePlugin", "SamplePlugin.MySamplePlugin");
        instance2.DrawingControl();

        //Now we want to prove, that this additional assembly was not loaded to prmiary app domain. 
        DrawControlsDefault();

        //And that we still have the old assembly loaded in previous AppDomain.
        instance.DrawingControl();

        //App domain is unloaded so, we will get exception if we try to call any of this object method.
        AppDomain.Unload(apd);
        try
        {
            instance.DrawingControl();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }

        Console.ReadKey();
    }
}

}

阴影复制似乎非常方便。