利用MEF实现插件机制（可根据输入类型来加载特定dll）

   最近在做PACS的项目中想利用插件来加载各个不同的SCP的操作实现。比如Worklist的查询数据库，可以有多个实现。 比如MPPS的更新，也可以有多个实现。 为了统一弹性处理插件模块，增加了类型输入，用来只加载特定的服务的实现。 

   [InheritedExport(typeof(ISCPBase))]     public interface ISCPBase     {         ISCPCfg SCPCfg         {             get;             set;         }           string CustomModuleName         {             get;         }     } 

   public class CustomExtensionManager     {         [ImportMany(typeof(ISCPBase), AllowRecomposition = true)]         public IEnumerable<ISCPBase> CustomModules { get; set; }           public CompositionContainer Container;           private Type[] _filterTypes;           private ModulesManagerCfg _mgrCfg;         public ModulesManagerCfg ModulesManagerConfig         {             get             {                 if (_mgrCfg == null)                 {                     try                     {                         _mgrCfg = XmlSerializeHelper<ModulesManagerCfg>.LoadFromFile(@"ModulesManagerCfg.xml");                     }                     catch (Exception ex)                     {                         Logger.ErrorWithFormat("Failed to load ModulesManagerCfg from ModulesManagerCfg.xml. {0}", ex.Message);                     }                       if (_mgrCfg == null)                         Logger.Error("ModulesManagerCfg is null, please check whether ModulesManagerCfg.xml exists.");                 }                   return _mgrCfg;             }         }           /// <summary>         /// Initialize the custom modules by interface type. It is well you can spec types.         /// If you do not care types, you can pass null. It will load all modules if inherited from ISCPBase.         /// </summary>         /// <param name="scpTypes">The type that inherited from ISCPBase. Like IWorklistQuery...</param>         public void Initialize(params Type[] scpTypes)         {             try             {                 if (null != scpTypes)                 {                     _filterTypes = scpTypes;                       var catalog = new AggregateCatalog(new TypeCatalog(scpTypes), new DirectoryCatalog(AppDomain.CurrentDomain.BaseDirectory));                       Container = new CompositionContainer(catalog);                 }                 else                 {                     var catalog = new AggregateCatalog(new TypeCatalog(scpTypes), new DirectoryCatalog(AppDomain.CurrentDomain.BaseDirectory));                       Container = new CompositionContainer(catalog);                 }                   Container.ComposeParts(this);             }             catch (Exception ex)             {                 Logger.ErrorWithFormat("Failed to initialize CustomExtensionManager. {0}", ex.Message);             }         }           public ISCPBase GetCurrentUsedModule()         {             if (null == ModulesManagerConfig)             {                 throw new ArgumentNullException("ModulesManagerCfg is null, please check whether ModulesManagerCfg.xml exists.");             }               if (String.IsNullOrEmpty(ModulesManagerConfig.CurrentUsedModuleName))             {                 throw new Exception("CurrentUsedModuleName is empty, please check ModulesManagerCfg.xml.");             }               if (null == Container)             {                 throw new Exception("Modules container is null, you can check your custom module and call Initialize() function to load modules.");             }               //var m = _container.GetExports<ISCPBase>()             //    .Where(e => e.Value.CustomModuleName.Equals(ModulesManagerConfig.CurrentUsedModuleName))             //    .FirstOrDefault();               //if (null != m)             //{             //    return m.Value;             //}               //return null;               if (null == _filterTypes)             {                 var m = CustomModules.FirstOrDefault(e => e.CustomModuleName.Equals(ModulesManagerConfig.CurrentUsedModuleName));                 return m;             }             else             {                  var m = from c in CustomModules

                         where _filterTypes.All(f => f.IsAssignableFrom(c.GetType()))

                          select c;

                   return m.FirstOrDefault();             }         }     }