模块化程序.在主机中调用函数

我使用构建了一个模块化程序

http://www.codeproject.com/Articles/258681/Windows-Forms-Modular-App-using-MEF作为基础，我有几个模块在工作。

这是一个MDI Windows窗体应用程序，我需要回叫主机模块来获取一些东西。

a） MDI主机窗口的位置信息

b） 写入主机窗口中的状态栏。

我已经设法编译了应用程序，但当我调用主机函数时，它总是给我一个空异常

我确实看过使用C#的MEF，我如何从插件中调用主机上的方法？

这就是我的线路

public Exec.Core.Interfaces.IHost Host;

但是主机总是空的，所以我在尝试访问作为主机的MDIForm的成员时会遇到异常。

即使我做公共Exec.Core.Interfaces.IHost主机｛get；set；｝

这就是主机。

NameSpace Exec
{
  [Export(typeof(Exec.Core.Interfaces.IHost))]
   //  MDIForm is the host.    
  public partial class MDIForm : Form, Exec.Core.Interfaces.IHost
  {
     ///other stuff not related to the problem

      // defined in public interface IHost
    public Point myLocation()
    {
      return this.Location;  // need the window location
    }
      // defined in public interface IHost
    public IHost GetHost()
    {  // is this what GetHost Should Return? Not sure
      return this;
    }
      // defined in public interface IHost
    public void SendMessage(string message)
    {
      SetStatusBar(message); // print a message to MDIForm status bar
    }
  }
}

然后是IHosts.cs

namespace Exec.Core.Interfaces
{
    public interface IHost
    {
        IHost GetHost();
        void SendMessage(string message);
        Point myLocation();
       // MDIForm GetThis( );  /* this gives error. Can't resolve MDIForm
                                  I don't know why and can't resolve.*/
    }
}

这是我试图从主机获取内容的模块之一

namespace Exec.Modules.Tasks
{
   [Export]
   public partial class frmTasks : Form
   {
       [Import(typeof (Exec.Core.Interfaces.IHost))] 
       public Exec.Core.Interfaces.IHost Host;
           // unfortunately Host == NULL at this point
       private void SendMessage (string message)
       {
           try
           {
              Host.SendMessage(message);  <Throws System.NullReferenceException
           }
           catch (Exception ex)
           {
              MessageBox.Show(ex.ToString());
           }
       }
       private IHost WhichHost()
       {
           try
           {     /// not really sure what will be returned here
               return GetHost();<Throws System.NullReferenceException
           }
           catch (Exception ex)
           {
               MessageBox.Show(ex.ToString());
            }
       }
       private Point Location()
       {
          try
          {
             return mylocation(); <Throws  System.NullReferenceException
          }
          catch (Exception ex)
          {
              MessageBox.Show(ex.ToString());
          }
       }
   }
}

最后，这就是我如何将所有对象放在ModuleHandler.cs中这几乎是从上面的代码项目中截取的，将一些方法调用分离为两部分，这样我就可以理解它为什么会消亡。

 namespace Exec.Core   
 {
     [Export(typeof(IModuleHandler))]
     public class ModuleHandler : IDisposable, IModuleHandler
     {
        [ImportMany(typeof(IModule), AllowRecomposition = true)]
         // The ModuleList will be filled with the imported modules
        public List<Lazy<IModule, IModuleAttribute>> ModuleList
        { get; set; }
        [ImportMany(typeof(IMenu), AllowRecomposition = true)]
        // The MenuList will be filled with the imported Menus
        public List<Lazy<IMenu, IModuleAttribute>> MenuList { get; set; }
        [Import(typeof(IHost))]
        // The imported host form
        public IHost Host { get; set; }

       AggregateCatalog catalog = new AggregateCatalog();
       public void InitializeModules()
       {
          // Create a new instance of ModuleList
          ModuleList = new List<Lazy<IModule, IModuleAttribute>>();
          // Create a new instance of MenuList
          MenuList = new List<Lazy<IMenu, IModuleAttribute>>();
          // Foreach path in the main app App.Config      
          foreach (var s in ConfigurationManager.AppSettings.AllKeys)
          {
            if (s.StartsWith("Path"))
            {
             // Create a new DirectoryCatalog with the path loaded from the App.Config
                DirectoryCatalog cataloglist = new DirectoryCatalog(ConfigurationManager.AppSettings[s], "jobexe*.dll");
               catalog.Catalogs.Add(cataloglist);
             }
           }
            // Create a new catalog from the main app, to get the Host
           catalog.Catalogs.Add( new AssemblyCatalog(System.Reflection.Assembly.GetCallingAssembly()));
                    // Create a new catalog from the ModularWinApp.Core
            DirectoryCatalog catalogExecAssembly = new DirectoryCatalog( System.IO.Path.GetDirectoryName(
              System.Reflection.Assembly.GetExecutingAssembly().Location ), "exe*.dll");
            catalog.Catalogs.Add(catalogExecAssembly);
            // Create the CompositionContainer
            CompositionContainer cc = new CompositionContainer(catalog);
            try
            {
                cc.ComposeParts(this);
            }
            catch (ReflectionTypeLoadException e)
            { MessageBox.Show(e.ToString()); }
            catch (ChangeRejectedException e)
            { MessageBox.Show(e.ToString()); }     
        }            
    }
}

因此，模块独立工作，但无法调用回主机。想知道我做错了什么。

提前感谢的任何帮助

最后一件事可能与这个问题有关。

这是启动程序的代码

 public static ModuleHandler _modHandler = new ModuleHandler();
static void Main()
{
   Application.EnableVisualStyles();
   Application.SetCompatibleTextRenderingDefault(false);
  //Initialize the modules. Now the modules will be loaded.
   _modHandler.InitializeModules();
    // this goes straight to class MDIForm()  constructor
  Application.Run(_modHandler.Host as Form);
}

Colin

cc.ComposeParts(this);

[Import(typeof (Exec.Core.Interfaces.IHost))] 
public Exec.Core.Interfaces.IHost Host;

namespace Exec
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        /// 
        //Create a new instance of ModuleHandler. Only one must exist.
        public static ModuleHandler _modHandler = new ModuleHandler();
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            //Initialize the modules. Now the modules will be loaded.
          _modHandler.InitializeModules();

          Application.Run(_modHandler.Host as Form);

        }
    }
}

public static ModuleHandler _modHandler = new ModuleHandler();

public static class Program

namespace Exec.Modules.Tasks

public partial class frmTasks : Form
{
       [Import(typeof (Exec.Core.Interfaces.IHost))] 
       public Exec.Core.Interfaces.IHost Host;
      private void Load_Form(object sender, EventArgs e)
      {
         Host = Program._modHandler.Host.GetHost; << added this to initialize host
           other stuff....
      }
      other stuff that now works
}