MEF的一个例子

MEF(Managed Extensibility Framework) .net framework4.0 加入，system.componentModel.composition

MEF与MAF(Managed Addin Framework)最大不同在于：前者关注使用非常简单的方式来支持具有很强灵活性的可扩展支持，后者关注具有物理隔离、安全、多版本支持的插件平台架构;

MEF和Unity不同在于：前者强调组合，后者强调依赖注入。

namespace Interfaces
{
    public interface IPlugin
    {
       void Write();
    }
}

namespace OnePlugin
{
 [Export(typeof(IPlugin))]
    public class OnePlugin:IPlugin
    {
        public void Write()
        {
            Console.WriteLine("one plugin");
        }
    }
}

namespace TwoPlugin
{
    [Export(typeof(IPlugin))]
    public class TwoPlugin:IPlugin
    {
        public void Write()
        {
            Console.WriteLine("two plugin");
        }
    }
}

　　

namespace MEFSample
{
    class Program
    {
        static void Main(string[] args)
        {
            //使用反射的插件实现
            //IEnumerable<Type> pluginTypes = GetPluginTypes();
            //foreach (Type type in pluginTypes )
            //{
            //    IPlugin plugin = (IPlugin)Activator.CreateInstance(type);
            //    plugin.Write();
            //}
            PluginProvider provider = new PluginProvider();
            foreach (Lazy <IPlugin> plugin in provider .Plugins)
            { plugin.Value.Write(); }
            Console.Read();
        }

        /// <summary>
        /// 使用反射的插件实现
        /// </summary>
        /// <returns></returns>
        public static IEnumerable<Type> GetPluginTypes()
        {
            string root = AppDomain.CurrentDomain.BaseDirectory;
            string[] files = Directory.GetFiles(root,"*.dll", SearchOption.TopDirectoryOnly);
            List<Type> types = new List<Type>();
            foreach (string file in files)
            {
                Type[] typearray = Assembly.LoadFrom(file).GetTypes();
                foreach (Type type in typearray) types.Add(type);
            }
            return from type in types where type.IsClass && (typeof(IPlugin).IsAssignableFrom(type)) select type;  
            //或者用yield return 
        }
    }

    public class PluginProvider
    {
        [ImportMany]
        public IEnumerable<Lazy<IPlugin>> Plugins { get; private set; }
        //[Import]
        //public Lazy<IPlugin> PluginOne;
        public PluginProvider ()
        {
               //var catalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());
               AggregateCatalog catalog = new AggregateCatalog();
               catalog.Catalogs.Add(new DirectoryCatalog("."));
            var container = new CompositionContainer(catalog);
            container.ComposeParts(this);
        }
    }
}

还可以命名：

public interface ILogger
{
    void WriteLog(string message);
}
    
[Export("TXT",typeof(ILogger))]
public class TXTLogger : ILogger
{
    public void WriteLog(string message)
    {
        System.Console.WriteLine(message);
    }
}

[Export("DB",typeof(ILogger))]
public class DBLogger : ILogger
{
    public void WriteLog(string message)
    {
        System.Console.WriteLine(message);
    }
}

[Export]
public class FacadeService
{
    [Import("TXT")]
    public ILogger TXTLogger { get; set; }

    [Import("DB")]
    public ILogger DBLogger { get; set; }
}

[Import]
public FacadeService Service { get; set; }

　　

public MainPage()
{
    InitializeComponent();
  
    var service = (Application.Current as App).Service;
    service.TXTLogger.WriteLog("写日志到文本文件");
    service.DBLogger.WriteLog("写日志到数据库");
}
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