[英]MEF-Import into Dictionary
Iam當前正在重構應用程序,並希望引入MEF。 Export類(Apple類)已完成,並用Export-keyword標記...在導入站點上,我目前有一個字典,其初始化如下所示:
Dictionary<int, Apple> dict = new Dictionary<int, Apple>();
for(int i=0; i < 10; i++)
dict.add(i, new Apple());
...
如何使用MEF初始化字典?
因此,我認為您的問題可以歸結為:“如何確保容器產生一個對象的多個實例,而不是每次請求都重復使用同一對象。” 嗯,這很容易-您只需指定CreationPolicy.NonShared
。
考慮一下IApple
示例實現:
public interface IApple { }
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(typeof(IApple))]
public class Apple : IApple
{
private static int appleCounter = 0;
private int id;
public Apple()
{
this.id = ++appleCounter;
}
public override string ToString()
{
return "Apple #" + this.id.ToString();
}
}
這是您可能使用它的一種方式:
class Program
{
public static void Main(string[] args)
{
var catalog = new ApplicationCatalog();
var container = new CompositionContainer(catalog);
IDictionary<int, IApple> dict = new Dictionary<int, IApple>();
for (int i = 0; i < 10; i++)
{
dict.Add(i, container.GetExportedValue<IApple>());
}
foreach (var pair in dict)
{
Console.WriteLine("{0}: {1}", pair.Key, pair.Value);
}
}
}
此處的代碼關鍵行是[PartCreationPolicy(CreationPolicy.NonShared)]
。 如果沒有這一點,將只有一個Apple
被創造出來。 當然,這並不像您期望的那樣有用。 這是生成字典的另一種方法,該方法更加靈活:
public interface IBasket
{
IDictionary<int, IApple> GetAppleDictionary();
}
[Export(typeof(IBasket))]
public class Basket : IBasket
{
private IDictionary<int, IApple> dict;
[ImportingConstructor]
public Basket([Import] CompositionContainer container)
{
this.dict = new Dictionary<int, IApple>();
for (int i = 0; i < 10; i++)
{
this.dict.Add(i, container.GetExportedValue<IApple>());
}
}
public IDictionary<int, IApple> GetAppleDictionary()
{
return dict;
}
}
class Program
{
[Import(typeof(IBasket))]
private IBasket basket = null;
public static void Main(string[] args)
{
var program = new Program();
program.Run();
}
private void Run()
{
var catalog = new ApplicationCatalog();
var container = CreateCompositionContainer(catalog);
container.ComposeParts(this);
foreach (var pair in this.basket.GetAppleDictionary())
{
Console.WriteLine("{0}: {1}", pair.Key, pair.Value);
}
}
private static CompositionContainer CreateCompositionContainer(ComposablePartCatalog catalog)
{
var wrappedCatalog = new AggregateCatalog(catalog, new TypeCatalog(typeof (CompositionContainer)));
var container = new CompositionContainer(wrappedCatalog);
container.ComposeExportedValue(container);
return container;
}
}
這里最棘手的部分是CreateCompositionContainer
。 此方法確保CompositionContainer
本身可用於滿足其所組成對象的導入。 這樣一來, Basket
可以直接操縱容器來生成所需的所有蘋果。
只是出於演示目的,這是您還可以使用[ImportMany]
屬性完成類似操作的一種方法(盡管所有這些[Export]
確實讓我畏縮了):
public interface IApple { }
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(typeof(IApple))]
[Export(typeof(IApple))]
/* ..repeat N times.. */
[Export(typeof(IApple))]
public class Apple : IApple
{
private static int appleCounter = 0;
private int id;
public Apple()
{
this.id = ++appleCounter;
}
public override string ToString()
{
return "Apple #" + this.id.ToString();
}
}
class Program
{
[ImportMany(typeof(IApple))]
private IEnumerable<IApple> apples = null;
public static void Main(string[] args)
{
var program = new Program();
program.Run();
}
void Run()
{
var catalog = new AssemblyCatalog(this.GetType().Assembly);
var container = new CompositionContainer(catalog);
container.ComposeParts(this);
apples.Dump();
}
}
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