c# - Ninject 相当于 MEF AssemblyCatalog

Question

在 MEF 中，AssemblyCatalog 用于扫描程序集以查找所有导出类型并配置容器。有 Ninject 的等效项吗？

var catalog = new AggregateCatalog();
catalog.Catalogs.Add(new AssemblyCatalog(Assembly.GetExecutingAssembly()));
var container = new CompositionContainer(catalog);

Answer 1

在 Ninject 中，使用类型属性和扫描程序集来添加绑定(bind)的能力是由名为 Ninject.Extensions.Conventions 的扩展提供的。 .

1. 添加约定包，例如使用包管理器控制台:

   Install-Package Ninject.Extensions.Conventions
   

2. 创建一些自定义属性以用于您的服务。这将等效于 MEF 中的 ExportAttribute:

   public enum ExportScope
   {
       Singleton,
       Transient
   }
   
   [AttributeUsage(AttributeTargets.Class)]
   public class ExportAttribute : Attribute
   {
       public ExportAttribute(Type serviceInterface, ExportScope scope = ExportScope.Singleton)
       {
           this.ServiceInterface = serviceInterface;
           this.Scope = scope;
       }
   
       public Type ServiceInterface { get; set; }
   
       public ExportScope Scope { get; set; }
   }
   

3. 创建自定义 BindingGenerator，它使用我们的 ExportAttribute 将类型绑定(bind)到给定接口(interface):

   public class ExportAttributeBindingGenerator : IBindingGenerator
   {
       public IEnumerable<IBindingWhenInNamedWithOrOnSyntax<object>> CreateBindings(Type type, IBindingRoot bindingRoot)
       {
           var attribute = type.GetCustomAttribute<ExportAttribute>();
           var serviceType = attribute.ServiceInterface;
   
           if (!serviceType.IsAssignableFrom(type))
           {
               throw new Exception(string.Format("Error in ExportAttribute: Cannot bind type '{0}' to type '{1}'.", 
                   serviceType, type));
           }
   
           var binding = bindingRoot.Bind(serviceType).To(type);
   
           switch (attribute.Scope)
           {
               case ExportScope.Singleton:
                   yield return (IBindingWhenInNamedWithOrOnSyntax<object>) binding.InSingletonScope();
                   break;
               case ExportScope.Transient:
                   yield return (IBindingWhenInNamedWithOrOnSyntax<object>) binding.InTransientScope();
                   break;
               default:
                   throw new ArgumentOutOfRangeException();
           }
       }
   }
   

4. 创建一个扩展方法以在内核上使用并添加约定:

   public static class NinjectBindingExtensions
   {
       public static void BindExportsInAssembly(this IBindingRoot root, Assembly assembly)
       {
           root.Bind(c => c.From(assembly)
                             .IncludingNonePublicTypes()
                             .SelectAllClasses()
                             .WithAttribute<ExportAttribute>()
                             .BindWith<ExportAttributeBindingGenerator>());
       }
   }
   

对于如此普通的东西，现在看起来需要做很多工作，但它非常灵活且可扩展。它做任何你想让它做的事。把它放在一个实用程序类库中，然后像这样在任何你想使用的地方使用它:

[Export(typeof(IFoo))]
public class Foo : IFoo
{

}

[Export(typeof(IBar), ExportScope.Transient)]
public class Bar : IBar
{

}

[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestNinjectConventions()
    {
        var kernel = new StandardKernel();

        kernel.BindExportsInAssembly(typeof(IFoo).Assembly);

        kernel.Get<IFoo>().Should().Be(kernel.Get<IFoo>());
        kernel.Get<IBar>().Should().NotBe(kernel.Get<IBar>());
    }
}