MEF Lazy ImportMany with Creationpolicy.NonShared
我是 MEF 的初学者，所以我有一个问题:) 我有以下内容：
[PartCreationPolicy(CreationPolicy.Shared)]
[Export(typeof(SharedExport))]
public class SharedExport : INPCBase
{
[ImportMany(typeof(INonShared),RequiredCreationPolicy = CreationPolicy.NonShared)]
private IEnumerable<Lazy<INonShared,Dictionary<string,object>>> fac;
...
public void Open()
{
foreach (var lazy in fac)
{
this.Muster.Add(lazy.Value);
}
}
导入的类全部标记为非共享。
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(typeof(INonShared))]
[ExportMetadata("Muster","030")]
public sealed class NonShared1 : INPCBase, INonShared
{
public NonShared1()
{
Debug.WriteLine("ctor NonShared1" + this.GetHashCode().ToString());
}
#region Implementation of INonShared
public string Displayname
{
get { return "Muster 030 "+ this.GetHashCode().ToString();
}
}
#endregion
}
现在我的问题：当 Open() 执行时，不应该总是创建一个新的 NonShared1 实例吗？我总是一样。
i'm a beginner in mef and so i have a question :)
i have the following:
[PartCreationPolicy(CreationPolicy.Shared)]
[Export(typeof(SharedExport))]
public class SharedExport : INPCBase
{
[ImportMany(typeof(INonShared),RequiredCreationPolicy = CreationPolicy.NonShared)]
private IEnumerable<Lazy<INonShared,Dictionary<string,object>>> fac;
...
public void Open()
{
foreach (var lazy in fac)
{
this.Muster.Add(lazy.Value);
}
}
the imported classes all marked as nonshared.
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(typeof(INonShared))]
[ExportMetadata("Muster","030")]
public sealed class NonShared1 : INPCBase, INonShared
{
public NonShared1()
{
Debug.WriteLine("ctor NonShared1" + this.GetHashCode().ToString());
}
#region Implementation of INonShared
public string Displayname
{
get { return "Muster 030 "+ this.GetHashCode().ToString();
}
}
#endregion
}
now my question: when Open() execute, shouldn't there always a new NonShared1 instance be created? i got always the same.
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评论（2）
马修关于共享/非共享方面仅影响每次导入时给出的实例的说法是正确的，每次拉取 Lazy.Value 时都不会获得新实例。如果您想要每次获取一个新实例并处理它，您可能会考虑使用 ExportFactory。目前 ExportFactory 仅存在于 Silverlight 版本的 MEF 中，但如果您确实需要此功能，mef.codeplex.com 上有一个示例项目，可以将该功能添加到桌面版本的 MEF 中。
Matthew is correct about the Shared/NonShared aspect only affecting the instance given at each import, you will not get a new instance every time you pull on Lazy.Value. If what you want is to get a new instance each time and dispose it you might look into using ExportFactory. Currently ExportFactory only exists in the Silverlight version of MEF but there is a sample project on mef.codeplex.com that adds the functionality to the desktop version of MEF if you really need this functionality.
不，因为 Lazy<>实例。
Lazy专为延迟加载值而设计。该值是在您第一次访问.Value属性时创建的，此后对该属性的所有访问都会返回相同的实例。 NonShared/Shared 创建策略在导入过程中发挥作用，因此通过属性注入、构造函数注入、字段注入、.GetExportedValue等...No, because of the Lazy<> instance. A
Lazy<T>is designed for lazy loading of a value. The value is created the first time you access the.Valueproperty, and the same instance is returned for all access to that property thereafter. The NonShared/Shared creation policy comes into play doing the import process, so through property injection, constructor injection, field injection, .GetExportedValueetc...