基于ASP.NET MVC3 Razor的模块化/插件式架构实现

本文主要探讨了一种基于ASP.NET MVC3 Razor的模块化（Plugin）/插件（plugin）式架构的实现方法。本文借鉴了《Compile your asp.net mvc Razor views into a seperate dll》作者提供的方法。

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敬请注意。其实ASP.NET MVC的模块化（Plugin）/插件（plugin）式架构讨论的很多，但基于Razor视图引擎的很少（如：MVC2插件架构例子都是基于WebForm的，MVCContrib Portable Areas也是，还有这个Plugin架构）。要么就是非常复杂非常重量级的框架，例如Orchard CMS的模块化做的很好，可惜太重量级了，也没独立的模块可以剥离出来。所以我们追寻的是简单的基于ASP.NET MVC3 Razor的模块化（Plugin）/插件（plugin）式架构的实现方法。本文最后实现的项目结构如下图：（插件都放到~/Plugin目录下，按功能划分模块，每个模块都有M,V,C）

其中，业务模块（class library project）包含其所有的视图、控制器等，模型可以放在里面也可以单独放一个project。主web项目没有引用业务模块，业务模块会编译到主web项目的~/plugin目录下面（注意：不是bin目录），然后当web应用启动的时候自动加载plugin目录下面的模块。最后运行起来的效果如下图：

其中红色的区域都是plugin进去的，那个tab的标题plugin到母版页的主菜单，tab内容也来自plugin。下面说说如何实现这样的ASP.NET MVC插件式plugin架构（模块化架构）。

实现的难点在动态加载UI视图（*.cshtml, _layout.cshtml, _viewStart.cshtml)

废话少说，直入要害。基于ASP.NET MVC3 Razor的编译发生在两个层面：

• 控制器（Controller）, 模型（Models），和其它所有的C#代码等有msbuild（或者VisualStudio）编译到bin目录下的程序集（assembly）
• 视图（*.aspx, *.cshtml）由ASP.NET在运行时动态编译。当一个Razor视图（*.cshtml）显示前，Razor视图引擎调用BuildManager把视图(*.cshtml)编译到动态程序集assembly，然后使用Activator.CreateInstance来实例化新编译出来的对象，最后显示出来。如果视图(*.cshtml)用到@model绑定model，那么还会自动加载bin或者GAC里面的Model。

所以如果我们要动态加载插件（plugin），用反射bin目录下的程序集（assembly）的方法很容易搞定上面的第一部分（C#代码的部分），但UI视图的部分（上面第二部分）（特别是*.cshtml, 母版_layout.cshtml, 基视图_viewStart.cshtml）就比较难搞定。而且每次报错都是一样的，那就是Controller找不到相应的视图View，基本不知所云而且根本不是要点：view …. or its master was not found or no view engine supports the searched locations. The following locations were searched: …，因此要搞定UI视图的部分（上面第二部分）（特别是*.cshtml, 母版_layout.cshtml, 基视图_viewStart.cshtml），就需要自己动手了，基本原理是：

• 重载RazorBuildProvider，用来动态编译视图
• 实现一个自定义VirtualPathProvider，从虚拟路径自定义判断读取资源（从插件中加载资源），如果要使用编译的视图就返回编译的VirtualFile
• 实现一个容器Dictionary保存已编译的视图和虚拟路径，例如path <~/views/team/index.cshtml> type <Area.Module2.Views.Team._Page_Views_Team_Index_cshtml>，或者path <~/views/_viewstart.cshtml> type <Area.Module1.Views._Page_Views__ViewStart_cshtml>

代码：自定义VirtualPathProvider，从虚拟路径自定义判断读取资源（从插件中加载资源），如果要使用编译的视图就返回编译的VirtualFile

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Web.Caching;
using System.Web.Hosting;
using System.Web.WebPages;

namespace Common.Framework
{
    public class CompiledVirtualPathProvider: VirtualPathProvider
    {
        /// <summary>
        /// Gets a value that indicates whether a file exists in the virtual file system.
        /// </summary>
        /// <returns>
        /// true if the file exists in the virtual file system; otherwise, false.
        /// </returns>
        /// <param name="virtualPath">The path to the virtual file.</param>
        public override bool FileExists(string virtualPath)
        {
            return
                GetCompiledType(virtualPath) != null
                || Previous.FileExists(virtualPath);
        }

        public Type GetCompiledType(string virtualPath)
        {
            return ApplicationPartRegistry.Instance.GetCompiledType(virtualPath);
        }

        /// <summary>
        /// Gets a virtual file from the virtual file system.
        /// </summary>
        /// <returns>
        /// A descendent of the <see cref="T:System.Web.Hosting.VirtualFile"/> class that represents a file in the virtual file system.
        /// </returns>
        /// <param name="virtualPath">The path to the virtual file.</param>
        public override VirtualFile GetFile(string virtualPath)
        {
            if (Previous.FileExists(virtualPath))
            {
                return Previous.GetFile(virtualPath);
            }
            var compiledType = GetCompiledType(virtualPath);
            if (compiledType != null)
            {
                return new CompiledVirtualFile(virtualPath, compiledType);
            }
            return null;
        }

        public override System.Web.Caching.CacheDependency GetCacheDependency(string virtualPath, System.Collections.IEnumerable virtualPathDependencies, DateTime utcStart)
        {
            if (virtualPathDependencies == null)
                return Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);

            return Previous.GetCacheDependency(virtualPath,
                    from vp in virtualPathDependencies.Cast<string>()
                    where GetCompiledType(vp) == null
                    select vp
                  , utcStart);
        }

    }
}

代码：容器Dictionary保存已编译的视图和虚拟路径，例如path <~/views/team/index.cshtml> type <Area.Module2.Views.Team._Page_Views_Team_Index_cshtml>，路径注册以后，会从容器库全局搜索所有注册过的视图，也就是说即使你视图引用的_layout.cshtml和_viewStart.cshtml在其他的Class library project照样可以找到。

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Web;
using System.Web.WebPages;

namespace Common.Framework
{
    public class DictionaryBasedApplicationPartRegistry : IApplicationPartRegistry
    {
        private static readonly Type webPageType = typeof(WebPageRenderingBase);
        private readonly Dictionary<string, Type> registeredPaths = new Dictionary<string, Type>();

        /// <summary>
        ///
        /// </summary>
        /// <param name="virtualPath"></param>
        /// <returns></returns>
        public virtual Type GetCompiledType(string virtualPath)
        {
            if (virtualPath == null) throw new ArgumentNullException("virtualPath");

            //Debug.WriteLine(String.Format("---GetCompiledType : virtualPath <{0}>", virtualPath));

            if (virtualPath.StartsWith("/"))
                virtualPath = VirtualPathUtility.ToAppRelative(virtualPath);
            if (!virtualPath.StartsWith("~"))
                virtualPath = !virtualPath.StartsWith("/") ? "~/" + virtualPath : "~" + virtualPath;
            virtualPath = virtualPath.ToLower();
            return registeredPaths.ContainsKey(virtualPath)
                       ? registeredPaths[virtualPath]
                       : null;
        }

        public void Register(Assembly applicationPart)
        {
            ((IApplicationPartRegistry)this).Register(applicationPart, null);
        }

        public virtual void Register(Assembly applicationPart, string rootVirtualPath)
        {
            //Debug.WriteLine(String.Format("---Register assembly <{0}>, path <{1}>", applicationPart.FullName, rootVirtualPath));

            foreach (var type in applicationPart.GetTypes().Where(type => type.IsSubclassOf(webPageType)))
            {
                //Debug.WriteLine(String.Format("-----Register type <{0}>, path <{1}>", type.FullName, rootVirtualPath));

                ((IApplicationPartRegistry)this).RegisterWebPage(type, rootVirtualPath);
            }
        }

        public void RegisterWebPage(Type type)
        {
            ((IApplicationPartRegistry)this).RegisterWebPage(type, string.Empty);
        }

        public virtual void RegisterWebPage(Type type, string rootVirtualPath)
        {
            var attribute = type.GetCustomAttributes(typeof(PageVirtualPathAttribute), false).Cast<PageVirtualPathAttribute>().SingleOrDefault<PageVirtualPathAttribute>();
            if (attribute != null)
            {
                var rootRelativeVirtualPath = GetRootRelativeVirtualPath(rootVirtualPath ?? "", attribute.VirtualPath);

                //Debug.WriteLine(String.Format("---Register path/type : path <{0}> type <{1}>", rootRelativeVirtualPath.ToLower(),
                //                              type.FullName));
                registeredPaths[rootRelativeVirtualPath.ToLower()] = type;
            }
        }

        static string GetRootRelativeVirtualPath(string rootVirtualPath, string pageVirtualPath)
        {
            string relativePath = pageVirtualPath;
            if (relativePath.StartsWith("~/", StringComparison.Ordinal))
            {
                relativePath = relativePath.Substring(2);
            }
            if (!rootVirtualPath.EndsWith("/", StringComparison.OrdinalIgnoreCase))
            {
                rootVirtualPath = rootVirtualPath + "/";
            }
            relativePath = VirtualPathUtility.Combine(rootVirtualPath, relativePath);
            if (!relativePath.StartsWith("~"))
            {
                return !relativePath.StartsWith("/") ? "~/" + relativePath : "~" + relativePath;
            }
            return relativePath;
        }
    }
}

下面的代码很关键，用PreApplicationStartMethod关键字(.NET 4.0开始支持）使得代码在Application_Start之前执行。

有关[assembly: PreApplicationStartMethod(typeof(SomeClassLib.Initializer), "Initialize")]详细信息请参考这个页面和这个页面。

using System.Web;
using System.Web.Compilation;
using System.Web.Hosting;
using Common.Framework;
using Common.PrecompiledViews;

[assembly: PreApplicationStartMethod(typeof(PreApplicationStartCode), "Start")]

namespace Common.Framework
{
    public static class PreApplicationStartCode
    {
        private static bool _startWasCalled;

        public static void Start()
        {
            if (_startWasCalled)
            {
                return;
            }
            _startWasCalled = true;

            //Register virtual paths
            HostingEnvironment.RegisterVirtualPathProvider(new CompiledVirtualPathProvider());

            //Load Plugin Folder,
            PluginLoader.Initialize();
        }
    }
}

代码：PluginLoader，加载plugin目录里面的东东（assembly和module配置文件）

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Web;
using System.Web.Compilation;
using System.Web.Hosting;
using Common.Framework;
using Common.PrecompiledViews;

//[assembly: PreApplicationStartMethod(typeof(PluginLoader), "Initialize")]

namespace Common.PrecompiledViews
{
    public class PluginLoader
    {
        public static void Initialize(string folder = "~/Plugin")
        {
            LoadAssemblies(folder);
            LoadConfig(folder);
        }

        private static void LoadConfig(string folder, string defaultConfigName="*.config")
        {
            var directory = new DirectoryInfo(HostingEnvironment.MapPath(folder));
            var configFiles = directory.GetFiles(defaultConfigName, SearchOption.AllDirectories).ToList();
            if (configFiles.Count == 0) return;

            foreach (var configFile in configFiles.OrderBy(s => s.Name))
            {
                ModuleConfigContainer.Register(new ModuleConfiguration(configFile.FullName));
            }
        }

        private static void LoadAssemblies(string folder)
        {
            var directory = new DirectoryInfo(HostingEnvironment.MapPath(folder));
            var binFiles = directory.GetFiles("*.dll", SearchOption.AllDirectories).ToList();
            if (binFiles.Count == 0) return;

            foreach (var plug in binFiles)
            {
                //running in full trust
                //************
                //if (GetCurrentTrustLevel() != AspNetHostingPermissionLevel.Unrestricted)
                //set in web.config, probing to plugin\temp and copy all to that folder
                //************************
                var shadowCopyPlugFolder = new DirectoryInfo(AppDomain.CurrentDomain.DynamicDirectory);
                var shadowCopiedPlug = new FileInfo(Path.Combine(shadowCopyPlugFolder.FullName, plug.Name));
                File.Copy(plug.FullName, shadowCopiedPlug.FullName, true); //TODO: Exception handling here...
                var shadowCopiedAssembly = Assembly.Load(AssemblyName.GetAssemblyName(shadowCopiedPlug.FullName));

                //add the reference to the build manager
                BuildManager.AddReferencedAssembly(shadowCopiedAssembly);
            }
        }

        //private static AspNetHostingPermissionLevel GetCurrentTrustLevel()
        //{
        //    foreach (AspNetHostingPermissionLevel trustLevel in
        //        new AspNetHostingPermissionLevel[]
        //            {
        //                AspNetHostingPermissionLevel.Unrestricted,
        //                AspNetHostingPermissionLevel.High,
        //                AspNetHostingPermissionLevel.Medium,
        //                AspNetHostingPermissionLevel.Low,
        //                AspNetHostingPermissionLevel.Minimal
        //            })
        //    {
        //        try
        //        {
        //            new AspNetHostingPermission(trustLevel).Demand();
        //        }
        //        catch (System.Security.SecurityException)
        //        {
        //            continue;
        //        }

        //        return trustLevel;
        //    }

        //    return AspNetHostingPermissionLevel.None;
        //}

    }
}

此外，使用SingleFileGenerator的优点是性能提升，缺点是修改了视图就要重新编译。

如何让ASP.NET加载BIN目录之外的路径的Assembly

我们把各个模块编译出来的assembly和各个模块的配置文件自动放到一个bin平级的plugin目录，然后web应用启动的时候自动扫描这个plugin目录并加载各个模块plugin，这个怎么做到的？大家也许知道，ASP.NET只允许读取Bin目录下的assbmely，不可以读取其他路径，包括Bin\abc等，即使在web.config这样配置probing也不行：（不信你可以试一下）

<configuration> Element
  <runtime> Element
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <probing privatePath="bin;bin\abc;plugin;"/>
    </assemblyBinding>
   </runtime>
</configuration>

这个和TrustLevel有关，在Full Trust的情况下，可以这样读取非Bin目录下的assembly：

首先在和Bib平级的地方建一个目录Plugin，然后在模块class library project的属性里面加一个postBuildEvent，就是说在编译完成以后把模块的assbmely自动拷贝到主web项目的plugin目录：

copy /Y "$(TargetDir)$(ProjectName).dll" "$(SolutionDir)ModularWebApplication\Plugin\"
copy /Y "$(TargetDir)$(ProjectName).config" "$(SolutionDir)ModularWebApplication\Plugin\"

然后用下面的代码加载Plugin目录下的assembly：（只看LoadAssembly那一段）

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Web;
using System.Web.Compilation;
using System.Web.Hosting;
using Common.Framework;
using Common.PrecompiledViews;

//[assembly: PreApplicationStartMethod(typeof(PluginLoader), "Initialize")]

namespace Common.PrecompiledViews
{
    public class PluginLoader
    {
        public static void Initialize(string folder = "~/Plugin")
        {
            LoadAssemblies(folder);
            LoadConfig(folder);
        }

        private static void LoadConfig(string folder, string defaultConfigName="*.config")
        {
            var directory = new DirectoryInfo(HostingEnvironment.MapPath(folder));
            var configFiles = directory.GetFiles(defaultConfigName, SearchOption.AllDirectories).ToList();
            if (configFiles.Count == 0) return;

            foreach (var configFile in configFiles.OrderBy(s => s.Name))
            {
                ModuleConfigContainer.Register(new ModuleConfiguration(configFile.FullName));
            }
        }

        private static void LoadAssemblies(string folder)
        {
            var directory = new DirectoryInfo(HostingEnvironment.MapPath(folder));
            var binFiles = directory.GetFiles("*.dll", SearchOption.AllDirectories).ToList();
            if (binFiles.Count == 0) return;

            foreach (var plug in binFiles)
            {
                //running in full trust
                //************
                //if (GetCurrentTrustLevel() != AspNetHostingPermissionLevel.Unrestricted)
                //set in web.config, probing to plugin\temp and copy all to that folder
                //************************
                var shadowCopyPlugFolder = new DirectoryInfo(AppDomain.CurrentDomain.DynamicDirectory);
                var shadowCopiedPlug = new FileInfo(Path.Combine(shadowCopyPlugFolder.FullName, plug.Name));
                File.Copy(plug.FullName, shadowCopiedPlug.FullName, true); //TODO: Exception handling here...
                var shadowCopiedAssembly = Assembly.Load(AssemblyName.GetAssemblyName(shadowCopiedPlug.FullName));

                //add the reference to the build manager
                BuildManager.AddReferencedAssembly(shadowCopiedAssembly);
            }
        }

        //private static AspNetHostingPermissionLevel GetCurrentTrustLevel()
        //{
        //    foreach (AspNetHostingPermissionLevel trustLevel in
        //        new AspNetHostingPermissionLevel[]
        //            {
        //                AspNetHostingPermissionLevel.Unrestricted,
        //                AspNetHostingPermissionLevel.High,
        //                AspNetHostingPermissionLevel.Medium,
        //                AspNetHostingPermissionLevel.Low,
        //                AspNetHostingPermissionLevel.Minimal
        //            })
        //    {
        //        try
        //        {
        //            new AspNetHostingPermission(trustLevel).Demand();
        //        }
        //        catch (System.Security.SecurityException)
        //        {
        //            continue;
        //        }

        //        return trustLevel;
        //    }

        //    return AspNetHostingPermissionLevel.None;
        //}

    }
}

如果不是Full Trust，例如Medium Trust的情况下参考这个帖子《Developing-a-plugin-framework-in-ASPNET-with-medium-trust》。

如何在_layout.cshtml的主菜单注入plugin的菜单

在母版页_layout.cshtml有个主菜单，一般是这样写的：

<ul>
   <li>@Html.ActionLink("Home", "Index", "Home")</li>
   <li>@Html.ActionLink("About", "About", "Home")</li>
   <li>@Html.ActionLink("Team", "Index", "Team")</li>
</ul>

现在我们如何实现从模块插入plugin到这个主菜单呢？这个有点难。因为大家知道，_layout.cshml母版没有controller。怎么实现呢？方法是用controller基类，让所有controller继承自这个基类。然后在基类里面，读取plugin目录里面的配置文件，获取所有模块需要插入的主菜单项，然后放入viewBag，这样在_Layout.cshtml就可以获取viewBag，类似这样：

<ul>
   @foreach (MainMenuItemModel entry in ViewBag.MainMenuItems)
    {
        <li>@Html.ActionLink(entry.Text,
               entry.ActionName,
                entry.ControllerName)</li>
    }
</ul>

代码：基类Controller，读取plugin目录里面的配置文件，获取所有模块需要插入的主菜单项，然后放入viewBag

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Net.Mime;
using System.Text;
using System.Web.Mvc;

namespace Common.Framework
{
    public class BaseController : Controller
    {
        protected override void Initialize(System.Web.Routing.RequestContext requestContext)
        {
            base.Initialize(requestContext);

            // retireve data from plugins
            IEnumerable<ModuleConfiguration> ret = ModuleConfigContainer.GetConfig();

            var data = (from c in ret
                        from menu in c.MainMenuItems
                        select new MainMenuItemModel
                                   {
                                       Id = menu.Id, ActionName = menu.ActionName, ControllerName = menu.ControllerName, Text = menu.Text
                                   }).ToList();

            ViewBag.MainMenuItems = data.AsEnumerable();
        }

    }
}

代码：ModuleConfigContainer，用到单例模式，只读取一次

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Common.Framework
{
    public static class ModuleConfigContainer
    {
        static ModuleConfigContainer()
        {
            Instance = new ModuleConfigDictionary();
        }

        internal static IModuleConfigDictionary Instance { get; set; }

        public static void Register(ModuleConfiguration item)
        {
            Instance.Register(item);
        }

        public static IEnumerable<ModuleConfiguration> GetConfig()
        {
            return Instance.GetConfigs();
        }
    }
}

代码：ModuleConfigDictionary

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Common.Framework
{
    public class ModuleConfigDictionary : IModuleConfigDictionary
    {
        private readonly Dictionary<string, ModuleConfiguration>  _configurations = new Dictionary<string, ModuleConfiguration>();

        public IEnumerable<ModuleConfiguration> GetConfigs()
        {
            return _configurations.Values.AsEnumerable();
        }

        public void Register(ModuleConfiguration item)
        {
            if(_configurations.ContainsKey(item.ModuleName))
            {
                _configurations[item.ModuleName] = item;
            }
            else
            {
                _configurations.Add(item.ModuleName, item);
            }
        }
    }
}

代码：ModuleConfiguration，读取模块的配置文件

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace Common.Framework
{
    public class ModuleConfiguration
    {
        public ModuleConfiguration(string filePath)
        {
            try
            {
                var doc = XDocument.Load(filePath);
                var root = XElement.Parse(doc.ToString());

                if (!root.HasElements) return;

                var module = from e in root.Descendants("module")
                             //where e.Attribute("name").Value == "xxxx"
                             select e;

                if (!module.Any()) return;

                ModuleName = module.FirstOrDefault().Attribute("name").Value;

                var menus = from e in module.FirstOrDefault().Descendants("menu")
                            select e;

                if (!menus.Any()) return;

                var menuitems = menus.Select(xElement => new MainMenuItemModel
                                                             {
                                                                 Id = xElement.Attribute("id").Value,
                                                                 Text = xElement.Attribute("text").Value,
                                                                 ActionName = xElement.Attribute("action").Value,
                                                                 ControllerName = xElement.Attribute("controller").Value
                                                             }).ToList();

                MainMenuItems = menuitems;
            }
            catch
            {
                //TODO: logging
            }
        }
        public string ModuleName { get; set; }
        public IEnumerable<MainMenuItemModel> MainMenuItems { get; set; }
    }
}

每个模块的配置文件为{projectName}.config，格式如下：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <module name="Module2">
    <mainmenu>
      <menu id="modul2" text="Team" action="Index" controller="Team"/>
    </mainmenu>
  </module>
</configuration>

为了简单起见，只保留了注入主菜单的部分，为了让读者简单易懂。明白了以后你自己可以任意扩展…

代码：IModuleConfigDictionary，接口

模块配置文件{projectName}.config的位置：

为什么每个模块的Class library project都需要一个web.config呢？因为如果没有这个，那就没有Razor智能提示，大家可以参考这篇文章《How to get Razor intellisense for @model in a class library project》。

闲话几句插件式架构（Plugin Architecture）或者模块化（Modular）架构

插件式架构（Plugin Architecture）或者模块化（Modular）架构是大型应用必须的架构，关于什么是Plugin，什么是模块化模式，这种架构的优缺点等我就不说了，自己百谷歌度。关于.NET下面的插件式架构和模块化开发实现方法，基本上用AppDomain实现，当检测到一个新的插件Plugin时，实例化一个新的AppDomain并加载Assembly反射类等，由于AppDomain很好的隔离各个Plugin，所以跨域通信要用MarshalByRefObject类，具体做法可以参考这篇文章《基于AppDomain的"插件式"开发》。另外，有很多框架提供了模块化/插件开发的框架，例如Prism、MEF(Managed Extensibility Framework，.NET 4.0 内置)等。

客户端插件架构

还有一种插件架构是客户端插件架构（Javascript 模块化），如jQuery UI Widget Factory，Silk Project就是很好的例子。

本文源码下载

源码下载请点击此处。运行源码之前务必阅读此文和本文。注意：本文抛砖引玉，力求简单，易懂，并非完整的架构实现，更多丰富的功能实现一切皆有可能，只要在理解的基础上。