试图弄清楚这个MEF组合错误意味着什么

Question

我有一个问题,我收到的以下异常试图完成一个电话.ComposeParts(this):

该组合物产生单一组成误差.根本原因如下.查看CompositionException.Errors属性以获取更多详细信息.

1)导出'CustomersModule.CustomerMenu(ContractName ="ModLibrary.IMenu")'不能分配给'System.Collections.Generic.IEnumerable`1 [[ModLibrary.IMenu,ModLibrary,Version = 1.0.0.0,Culture = neutral] ,PublicKeyToken = null]]'.

导致:无法在部分'ModAppWorks.Host'上设置导入'ModAppWorks.Host.Menus(ContractName ="ModLibrary.IMenu")'.元素:ModAppWorks.Host.Menus(ContractName ="ModLibrary.IMenu") - > ModAppWorks.Host

那里有一个部分似乎错误意味着IMenu必须实现IEnumerable.这是我的作文代码:

static class Program
{
    [STAThread]
    static void Main()
    {
        Host host = new Host();
        host.Run();
    }
}

class Host
{
    #region Init
    public Host()
    { }
    #endregion

    #region Functions
    public void Run()
    {
        Compose();

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new AppHost());
    }

    private void Compose()
    {
        var agrCatalog = new AggregateCatalog();
        var dirCatalog = new DirectoryCatalog(Path.GetDirectoryName
            (Assembly.GetExecutingAssembly().Location) + "..\\..\\..\\Extensions", "*.dll");
        var asmCatalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());

        agrCatalog.Catalogs.Add(dirCatalog);
        agrCatalog.Catalogs.Add(asmCatalog);

        var hostContainer = new CompositionContainer(agrCatalog);
        hostContainer.ComposeParts(this);
    }
    #endregion

    #region Properties
    [Import(typeof(IMenu))]
    public IEnumerable<IMenu> Menus { get; set; }
    #endregion

我正在导入一个实例a的类ToolStripMenuItem.我的出口样本:

[Export(typeof(IMenu))]
public class CustomerMenu : IMenu
{
    #region Fields
    private System.Windows.Forms.ToolStripMenuItem CustomerMainMenu;
    private System.Windows.Forms.ToolStripSeparator mnuSeparator;
    private System.Windows.Forms.ToolStripMenuItem CustomersMenuItem;
    #endregion

    #region Init
    public CustomerMenu()
    {
        InitializeComponent();
        // 
        // CustomerMenu
        // 
        this.CustomerMainMenu.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
        this.mnuSeparator,
        this.CustomersMenuItem});
        this.CustomerMainMenu.Name = "CustomerMenu";
        this.CustomerMainMenu.Size = new System.Drawing.Size(94, 20);
        this.CustomerMainMenu.Text = "Customer Menu";
        // 
        // toolStripMenuItem1
        // 
        this.mnuSeparator.Name = "toolStripMenuItem1";
        this.mnuSeparator.Size = new System.Drawing.Size(149, 6);
        // 
        // Customers
        // 
        this.CustomersMenuItem.Name = "Customers";
        this.CustomersMenuItem.Size = new System.Drawing.Size(152, 22);
        this.CustomersMenuItem.Text = "Customers";
    }

    #endregion

    #region Functions
    private void InitializeComponent()
    {
        this.CustomerMainMenu = new System.Windows.Forms.ToolStripMenuItem();
        this.mnuSeparator = new System.Windows.Forms.ToolStripSeparator();
        this.CustomersMenuItem = new System.Windows.Forms.ToolStripMenuItem();
    }

    #endregion

如果IMenu是未实现所需IEnumerable,没有人看到的东西我可能是做错了？

Answer 1

导入导出集合时,需要使用ImportMany属性对其进行明确说明.像这样更改属性属性:

[ImportMany(typeof(IMenu))] 
public IEnumerable<IMenu> Menus { get; set; } 

您还应该能够排除合同("typeof(Menu)"参数),因为您导入的是导出的相同类型.保留合同的导出属性.

[ImportMany] 
public IEnumerable<IMenu> Menus { get; set; }