[英]MEF-Import into Dictionary
Iam当前正在重构应用程序,并希望引入MEF。 Export类(Apple类)已完成,并用Export-keyword标记...在导入站点上,我目前有一个字典,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,我认为您的问题可以归结为:“如何确保容器产生一个对象的多个实例,而不是每次请求都重复使用同一对象。” 嗯,这很容易-您只需指定CreationPolicy.NonShared
。
考虑一下IApple
示例实现:
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();
}
}
这是您可能使用它的一种方式:
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);
}
}
}
此处的代码关键行是[PartCreationPolicy(CreationPolicy.NonShared)]
。 如果没有这一点,将只有一个Apple
被创造出来。 当然,这并不像您期望的那样有用。 这是生成字典的另一种方法,该方法更加灵活:
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;
}
}
这里最棘手的部分是CreateCompositionContainer
。 此方法确保CompositionContainer
本身可用于满足其所组成对象的导入。 这样一来, Basket
可以直接操纵容器来生成所需的所有苹果。
只是出于演示目的,这是您还可以使用[ImportMany]
属性完成类似操作的一种方法(尽管所有这些[Export]
确实让我畏缩了):
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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