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MEF:使用组合零件和从组合零件导出满足导出零件

composition mef silverlight .net c#

Pop Catalin · 技术社区 · 14 年前

我在Silverlight 4中有以下场景:

我有通知服务

代码段

[InheritedExport]
public interface INotificationsService : IObservable<ReceivedNotification>
{
    void IssueNotifications(IEnumerable<ClientIssuedNotification> notifications);
}

以及这项服务的实施代码段

[PartCreationPolicy(CreationPolicy.NonShared)]
public class ClientNotificationService : INotificationsService
{
    [Import]
    IPlugin Plugin { get; set; }
    ...
}

我怎么能告诉MEF ClientNotificationService的Plugin属性必须由导入INotificationsService的导入类提供呢。

代码段

public class Client
{
    [Export]
    IPlugin Current { get; set; }

    [Import]
    INotificationService NotificationService;
}

我怎么说我想让MEF满足ClientNotificationService.Plugin部分和客户端类导出的IPlugin。

或者如果有其他的方法,比如使用元数据来做这件事,我会很感激任何的见解。我已经挣扎了一段时间了。

2 回复 | 直到 14 年前

Matthew Abbott 14 年前

您可以导出允许您访问插件的委托,例如:

public class Client
{
    [Export("PluginDelegate")]
    IPlugin GetPlugin()
    {
        return new SamplePlugin();
    }

    [Import]
    public INotificationService NotificationService { get; set; }
}

[PartCreationPolicy(CreationPolicy.NonShared)]
public class ClientNotificationService : INotificationService
{
    [Import("PluginDelegate")] Func<IPlugin> PluginDelegate;
}

Wim Coenen 14 年前

基本上我想要通知服务,接收导入服务器提供的唯一ID

您可以将ID(以及它需要初始化的事实)添加到 INotificationsService 合同:

public interface INotificationsService : IObservable<ReceivedNotification>
{
    /// <summary>
    /// Gets or sets the ID for this notification service. May only be set once.
    /// </summary>
    /// <exception cref="InvalidOperationException">
    /// The setter was called more than once, or the getter was called before the
    /// ID was initialized.
    /// </exception>
    string ID { get; set; }

    void IssueNotifications(IEnumerable<ClientIssuedNotification> notifications);
}

导入可以如下所示:

public class Client
{
    private readonly INotificationsService _notificationsService;

    [Import(typeof(INotificationService), 
        RequiredCreationPolicy = CreationPolicy.NonShared)]
    public INotificationsService NotificationsService
    {
        get
        {
            return _notificationsService;
        }
        set
        {
           _notificationsService = value;
           _notificationsService.ID = "SomeID"; 
        }
    }
}

public interface INotificationsServiceFactory
{
   INotificationsService Create(string ID);
}

两种方法都有不同的优点和缺点。例如,导入时初始化方法很简单,但它在组件生命周期中引入了一个额外的阶段(“已创建但尚未初始化”)。

一实例。如果需要清理,工厂方法也将处理容器中物品的责任转移给工厂客户。