纸壳CMS的插件加载机制

纸壳CMS是一个开源的可视化设计CMS，通过拖拽，在线编辑的方式来创建网站。

GitHub

https://github.com/SeriaWei/ZKEACMS.Core

欢迎Star，Fork，发PR。:)

插件化设计

纸壳CMS是基于插件化设计的，可以通过扩展插件来实现不同的功能。如何通过插件来扩展，可以参考这篇文章：

http://www.zkea.net/codesnippet/detail/zkeacms-plugin-development.html

纸壳CMS的插件是相互独立的，各插件的引用也相互独立，即各插件都可引用各自需要的nuget包来达到目的。而不用把引用加到底层。

插件存放目录

纸壳CMS的插件的存放目录在开发环境和已发布的程序中是不一样的。在开发环境，插件和其它的项目统一放在src目录下：

而发布程序以后，插件会在wwwroot/Plugins目录下：

所以，如果在开发过程中要使用插件目录时，需要使用特定的方法来获取真实的目录，如：

PluginBase.GetPath<SectionPlug>()

相关代码

有关插件用到的所有相关代码，都在 EasyFrameWork/Mvc/Plugin 目录下：

插件加载

纸壳CMS在程序启动时加载所有启用的插件Loader.cs：

public IEnumerable<IPluginStartup> LoadEnablePlugins(IServiceCollection serviceCollection)
{
    var start = DateTime.Now;
    Loaders.AddRange(GetPlugins().Where(m => m.Enable && m.ID.IsNotNullAndWhiteSpace()).Select(m =>
    {
        var loader = new AssemblyLoader();
        loader.CurrentPath = m.RelativePath;
        var assemblyPath = Path.Combine(m.RelativePath, (HostingEnvironment.IsDevelopment() ? Path.Combine(AltDevelopmentPath) : string.Empty), m.FileName);

        Console.WriteLine("Loading: {0}", m.Name);

        var assemblies = loader.LoadPlugin(assemblyPath);
        assemblies.Each(assembly =>
        {
            if (!LoadedAssemblies.ContainsKey(assembly.FullName))
            {
                LoadedAssemblies.Add(assembly.FullName, assembly);
            }
        });
        return loader;
    }));
    Console.WriteLine("All plugins are loaded. Elapsed: {0}ms", (DateTime.Now - start).Milliseconds);
    return serviceCollection.ConfigurePlugin().BuildServiceProvider().GetPlugins();
}

AssemblyLoader

AssemblyLoader是加载插件DLL的关键，纸壳CMS主要通过它来加载插件，并加载插件的相关依赖，并注册插件。

namespace Easy.Mvc.Plugin
{
    public class AssemblyLoader
    {
        private const string ControllerTypeNameSuffix = "Controller";
        private static bool Resolving { get; set; }
        public AssemblyLoader()
        {
            DependencyAssemblies = new List<Assembly>();
        }
        public string CurrentPath { get; set; }
        public string AssemblyPath { get; set; }
        public Assembly CurrentAssembly { get; private set; }
        public List<Assembly> DependencyAssemblies { get; private set; }
        private TypeInfo PluginTypeInfo = typeof(IPluginStartup).GetTypeInfo();
        public IEnumerable<Assembly> LoadPlugin(string path)
        {
            if (CurrentAssembly == null)
            {
                AssemblyPath = path;
                
                CurrentAssembly = AssemblyLoadContext.Default.LoadFromAssemblyPath(path);
                ResolveDenpendency(CurrentAssembly);
                RegistAssembly(CurrentAssembly);
                yield return CurrentAssembly;
                foreach (var item in DependencyAssemblies)
                {
                    yield return item;
                }
            }
            else { throw new Exception("A loader just can load one assembly."); }
        }

        private void ResolveDenpendency(Assembly assembly)
        {
            string currentName = assembly.GetName().Name;
            var dependencyCompilationLibrary = DependencyContext.Load(assembly)
                .CompileLibraries.Where(de => de.Name != currentName && !DependencyContext.Default.CompileLibraries.Any(m => m.Name == de.Name))
                .ToList();

            dependencyCompilationLibrary.Each(libaray =>
            {
                bool depLoaded = false;
                foreach (var item in libaray.Assemblies)
                {
                    var files = new DirectoryInfo(Path.GetDirectoryName(assembly.Location)).GetFiles(Path.GetFileName(item));
                    foreach (var file in files)
                    {
                        DependencyAssemblies.Add(AssemblyLoadContext.Default.LoadFromAssemblyPath(file.FullName));
                        depLoaded = true;
                        break;
                    }
                }
                if (!depLoaded)
                {
                    foreach (var item in libaray.ResolveReferencePaths())
                    {
                        if (File.Exists(item))
                        {
                            DependencyAssemblies.Add(AssemblyLoadContext.Default.LoadFromAssemblyPath(item));
                            break;
                        }
                    }
                }
            });


        }

        private void RegistAssembly(Assembly assembly)
        {
            List<TypeInfo> controllers = new List<TypeInfo>();
            PluginDescriptor plugin = null;
            foreach (var typeInfo in assembly.DefinedTypes)
            {
                if (typeInfo.IsAbstract || typeInfo.IsInterface) continue;

                if (IsController(typeInfo) && !controllers.Contains(typeInfo))
                {
                    controllers.Add(typeInfo);
                }
                else if (PluginTypeInfo.IsAssignableFrom(typeInfo))
                {
                    plugin = new PluginDescriptor();
                    plugin.PluginType = typeInfo.AsType();
                    plugin.Assembly = assembly;
                    plugin.CurrentPluginPath = CurrentPath;
                }
            }
            if (controllers.Count > 0 && !ActionDescriptorProvider.PluginControllers.ContainsKey(assembly.FullName))
            {
                ActionDescriptorProvider.PluginControllers.Add(assembly.FullName, controllers);
            }
            if (plugin != null)
            {
                PluginActivtor.LoadedPlugins.Add(plugin);
            }
        }
        protected bool IsController(TypeInfo typeInfo)
        {
            if (!typeInfo.IsClass)
            {
                return false;
            }

            if (typeInfo.IsAbstract)
            {
                return false;
            }


            if (!typeInfo.IsPublic)
            {
                return false;
            }

            if (typeInfo.ContainsGenericParameters)
            {
                return false;
            }

            if (typeInfo.IsDefined(typeof(NonControllerAttribute)))
            {
                return false;
            }

            if (!typeInfo.Name.EndsWith(ControllerTypeNameSuffix, StringComparison.OrdinalIgnoreCase) &&
                !typeInfo.IsDefined(typeof(ControllerAttribute)))
            {
                return false;
            }

            return true;
        }
    }
}

注册插件时，需要将插件中的所有Controller分析出来，当用户访问到插件的对应Controller时，才可以实例化Controller并调用。

动态编译插件视图

ASP.NET MVC 的视图（cshtml）是可以动态编译的。但由于插件是动态加载的，编译器并不知道编译视图所需要的引用在什么地方，这会导致插件中的视图编译失败。并且程序也需要告诉编译器到哪里去找这个视图。PluginRazorViewEngineOptionsSetup.cs 便起到了这个作用。

由于开发环境的目录不同，对以针对开发环境，需要一个视图文件提供程序来解析视图文件位置：

if (hostingEnvironment.IsDevelopment())
{
    options.FileProviders.Add(new DeveloperViewFileProvider(hostingEnvironment));
}

loader.GetPlugins().Where(m => m.Enable && m.ID.IsNotNullAndWhiteSpace()).Each(m =>
{
    var directory = new DirectoryInfo(m.RelativePath);
    if (hostingEnvironment.IsDevelopment())
    {
        options.ViewLocationFormats.Add($"{DeveloperViewFileProvider.ProjectRootPath}{directory.Name}" + "/Views/{1}/{0}" + RazorViewEngine.ViewExtension);
        options.ViewLocationFormats.Add($"{DeveloperViewFileProvider.ProjectRootPath}{directory.Name}" + "/Views/Shared/{0}" + RazorViewEngine.ViewExtension);
        options.ViewLocationFormats.Add($"{DeveloperViewFileProvider.ProjectRootPath}{directory.Name}" + "/Views/{0}" + RazorViewEngine.ViewExtension);
    }
    else
    {
        options.ViewLocationFormats.Add($"/wwwroot/{Loader.PluginFolder}/{directory.Name}" + "/Views/{1}/{0}" + RazorViewEngine.ViewExtension);
        options.ViewLocationFormats.Add($"/wwwroot/{Loader.PluginFolder}/{directory.Name}" + "/Views/Shared/{0}" + RazorViewEngine.ViewExtension);
        options.ViewLocationFormats.Add($"/wwwroot/{Loader.PluginFolder}/{directory.Name}" + "/Views/{0}" + RazorViewEngine.ViewExtension);
    }
});
options.ViewLocationFormats.Add("/Views/{0}" + RazorViewEngine.ViewExtension);

为了解决引用问题，需要把插件相关的所有引用都加入到编译环境中：

loader.GetPluginAssemblies().Each(assembly =>
{
    var reference = MetadataReference.CreateFromFile(assembly.Location);
    options.AdditionalCompilationReferences.Add(reference);                
});