MEF目录为空

我正在使用一个使用MEF的WPF应用程序。但是，即使我运行下面的代码(作为代码中某处的测试代码片段)，目录始终是空的。所有的示例代码都做了同样的事情，这些都工作得很好。但是我的坏了。我错过了一些重要的东西，我自己也弄不清楚。所以，我需要一些帮助。

var catalog = new AggregateCatalog();        
var x = Assembly.GetExecutingAssembly().Location;
catalog.Catalogs.Add(
new DirectoryCatalog(
          Path.GetDirectoryName(
          Assembly.GetExecutingAssembly().Location)));
CompositionContainer container = new CompositionContainer(catalog);

这是实际的场景代码。同一解决方案中有3个项目

1. wpf Project.
扩展项目
2. 。
合同项目
3. 。

Extension项目包含Exports。合同项目包含wpf项目和Extension项目共享的接口。

[Export("LoginManager", typeof(IEmployeeLoginManager))]
public class LoginManager : IEmployeeLoginManager
{
    public EmployeeLoginModel LoginEmployee(String userName, string password) 
    {
        DEmployeeLoginManager employeeLoginManager = new DEmployeeLoginManager();
        return employeeLoginManager.LoginEmployee(userName, password);
    }
}

这个Export在WPF项目中使用如下，

public partial class LoginWindow
{
    public EmployeeLoginModel LoggedInEmployee;
    [Import("LoginManager",AllowDefault = true)]
    private IEmployeeLoginManager LoginManager;
    public LoginWindow()
    {
        InitializeComponent();
    }
    private void RadWindow_Closed_1(object sender, Telerik.Windows.Controls.WindowClosedEventArgs e)
    {
        Application.Current.Shutdown();
        Environment.Exit(0);
        return;
    }
    private void RadButton_Click_1(object sender, RoutedEventArgs e)
    {
        string passWord = PasswordText.Password;
        LoggedInEmployee.Password = passWord;
        var container = MEFLoader.GetMEFContainer();
        container.ComposeParts(this);
        EmployeeLoginModel employee= LoginManager.LoginEmployee(LoggedInEmployee.UserName, passWord);
        if (employee.LoginStatus == true) 
        {
            this.Close();
        }
    }

PS:这是MEFLoader类:

public static class MEFLoader
{
    public static CompositionContainer GetMEFContainer() 
    {
        var catalog = new AggregateCatalog(new DirectoryCatalog("."), new AssemblyCatalog(Assembly.GetExecutingAssembly()));
        var container = new CompositionContainer(catalog);
        return container as CompositionContainer;
    }
}

我是MEF的新手，我也很欣赏我代码中的任何改进点。

 var catalog = new AggregateCatalog();         
catalog.Catalogs.Add(
new DirectoryCatalog(
          Path.GetDirectoryName(
          Assembly.GetExecutingAssembly().Location)));
CompositionContainer container = new CompositionContainer(catalog);

copy $(TargetPath) $(SolutionDir)'[Your running application folder]'bin'Debug