我的 MEF 出口有什么问题吗？

Question

我收到一个错误：

An exception has occurred while trying to add a view to region 'MenubarRegion'. 
    - The most likely causing exception was was: 
      'Microsoft.Practices.ServiceLocation.ActivationException: Activation error occured 
      while trying to get instance of type MenuView, key "" ---> 

我的 MenuView 使用 MEF 通过 MenuViewModel 设置其数据上下文，MEF 又导入了 IServiceFactory 的一个实例。 我确信错误是由于 IServiceFactory 和 MEF 而发生的。 ....... 我的意思是出口或进口。 我猜这是因为当我删除 MenuViewModel 中的 ImportingConstructor 和 IServiceFactory 声明时，我的程序运行良好。

我已经使用 MefX 检查了 MEF 上的错误。 结果如下：

这是我的代码：

菜单视图.xaml.cs

[Export]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class MenuView : UserControlViewBase
{
    [ImportingConstructor]
    public MenuView(MenuViewModel viewModel)
    {
        InitializeComponent();
        this.DataContext = viewModel;
    }
}

菜单视图模型.cs

[Export]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class MenuViewModel : ViewModelBase
{

    IServiceFactory _ServiceFactory;

    [ImportingConstructor]
    public MenuViewModel(IServiceFactory serviceFactory)
    {
        _ServiceFactory = serviceFactory;
    }

    protected override void OnViewLoaded()
    {
        _MenuItems = new ObservableCollection<MenuItem>();

        WithClient<IMenuItemService>(_ServiceFactory.CreateClient<IMenuItemService>(), menuItemClient =>
        {
            MenuItem[] menuItems = menuItemClient.GetAllParentMenuItemsWithChildren();
            if (menuItems != null)
            {
                foreach (MenuItem menuItem in menuItems)
                {
                    _MenuItems.Add(menuItem);
                }

                _SelectedMenuItem = _MenuItems[2];
            }

        });
    }

    private ObservableCollection<MenuItem> _MenuItems;

    public ObservableCollection<MenuItem> MenuItems
    {
        get
        {
            return _MenuItems;
        }
        set
        {
            if (_MenuItems != value)
            {
                _MenuItems = value;
                OnPropertyChanged(() => MenuItems, false);
            }
        }
    }

    private MenuItem _SelectedMenuItem;

    public MenuItem SelectedMenuItem
    {
        get
        {
            return _SelectedMenuItem;
        }
        set
        {
            if (_SelectedMenuItem != value)
            {
                _SelectedMenuItem = value;
                OnPropertyChanged(() => SelectedMenuItem);
            }
        }
    }

}

服务工厂.cs

public interface IServiceFactory
{
    T CreateClient<T>() where T : IServiceContract;
}

服务工厂.cs

[Export(typeof(IServiceFactory))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class ServiceFactory : IServiceFactory
{
    public T CreateClient<T>() where T : IServiceContract
    {
        return ObjectBase.Container.GetExportedValue<T>();
    }
}

引导程序（客户端）：

public static class MEFLoader
{
    public static CompositionContainer Init()
    {
        return Init(null);
    }

    public static CompositionContainer Init(ICollection<ComposablePartCatalog> catalogParts)
    {
        AggregateCatalog catalog = new AggregateCatalog();

        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MenuItemClient).Assembly));
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MEFLoader).Assembly));

        if (catalogParts != null)
            foreach (var part in catalogParts)
                catalog.Catalogs.Add(part);

        CompositionContainer container = new CompositionContainer(catalog);

        return container;
    }
}

Bootstrapper（业务方面）

public static class MEFLoader
{
    public static CompositionContainer Init()
    {
        AggregateCatalog catalog = new AggregateCatalog();

        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MunimPlusEngine).Assembly));
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MenuItemManager).Assembly));
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MenuItemRepository).Assembly));
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MEFLoader).Assembly));

        CompositionContainer container = new CompositionContainer(catalog);

        return container;

    }
}

引导程序（WPF 主应用程序）

public class BootStrapper : MefBootstrapper
{
    protected override DependencyObject CreateShell()
    {
        return Container.GetExportedValue<Shell>();
    }

    protected override void InitializeShell()
    {
        base.InitializeShell();
        App.Current.MainWindow = (Window)Shell;
        App.Current.MainWindow.Show();
    }

    protected override void ConfigureAggregateCatalog()
    {
        base.ConfigureAggregateCatalog();
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(BootStrapper).Assembly));
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(RegionNames).Assembly));
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(ModuleMenu.Module).Assembly));
    }
}

应用程序.xaml.cs

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        ObjectBase.Container = MEFLoader.Init(new List<ComposablePartCatalog>()
                                                    {
                                                        new AssemblyCatalog(Assembly.GetExecutingAssembly())
                                                    });

        BootStrapper bootstrapper = new BootStrapper();
        bootstrapper.Run();

    }
}

项目

如果有人想看一下，这是我的项目：

下载项目

Answer 1

问题是您的ServiceFactory实现没有添加到 MEF 目录中。 添加时：

    public class BootStrapper : MefBootstrapper
{
    protected override DependencyObject CreateShell()
    {
        return Container.GetExportedValue<Shell>();
    }

    protected override void InitializeShell()
    {
        base.InitializeShell();
        App.Current.MainWindow = (Window)Shell;
        App.Current.MainWindow.Show();
    }

    protected override void ConfigureAggregateCatalog()
    {
        base.ConfigureAggregateCatalog();
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(BootStrapper).Assembly));
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(RegionNames).Assembly));
        AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(ModuleMenu.Module).Assembly));
        //Added catalog 
        //--> 
            AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(ServiceFactory).Assembly));
    }
}

到您的引导程序配置，应用程序停止在启动时抛出异常。 （但是它仍然没有显示任何内容）

为了添加该类型，我需要在主应用程序中添加对附加项目的引用。