我已经为这个问题苦苦挣扎了几天,但我仍然不知道如何解决它。
我为 Unity Container 创建了一个容器扩展,使我能够轻松地在容器中注册装饰器类。这是我目前拥有的实现,与本文中的实现几乎相同:
public class DecoratorExtension : UnityContainerExtension
{
private int m_order;
private Dictionary<Type, IList<DecoratorRegistration>> m_typeStacks;
protected override void Initialize()
{
m_typeStacks = new Dictionary<Type, IList<DecoratorRegistration>>();
Context.Registering += AddRegistration;
Context.Strategies.Add(new DecoratorBuildStrategy(m_typeStacks), UnityBuildStage.PreCreation);
}
private void AddRegistration(object _sender, RegisterEventArgs _e)
{
if (_e.TypeFrom == null || !_e.TypeFrom.IsInterface)
return;
GetStack(_e.TypeFrom)
.Add(new DecoratorRegistration {Order = m_order++, Type = _e.TypeTo});
}
private IList<DecoratorRegistration> GetStack(Type _type)
{
if (!m_typeStacks.ContainsKey(_type))
m_typeStacks.Add(_type, new List<DecoratorRegistration>());
return m_typeStacks[_type];
}
}
这样做是为每种类型使用一个列表,以存储同一目标类型的所有类型注册,以便在调用 Resolve 时使用此构建策略重新组装它:
internal class DecoratorBuildStrategy : BuilderStrategy
{
private readonly Dictionary<Type, IList<DecoratorRegistration>> m_typeStacks;
internal DecoratorBuildStrategy(Dictionary<Type, IList<DecoratorRegistration>> _typeStacks)
{
m_typeStacks = _typeStacks;
}
public override void PreBuildUp(IBuilderContext _context)
{
var key = _context.OriginalBuildKey;
if (_context.GetOverriddenResolver(key.Type) != null)
return;
// Only interfaces can use decorators.
if (!key.Type.IsInterface)
return;
// Gets the list of types required to build the 'decorated' instance.
// The list is reversed so that the least dependent types are built first.
var decoratorTypes = GetDecoratorTypes(key.Type).Reverse().ToList();
if (!decoratorTypes.Any())
return;
object value = null;
foreach (var type in decoratorTypes)
{
Type typeToBuild = type;
if (typeToBuild.IsGenericTypeDefinition)
{
Type[] genericArgumentTypes = key.Type.GetGenericArguments();
typeToBuild = typeToBuild.MakeGenericType(genericArgumentTypes);
}
value = _context.NewBuildUp(new NamedTypeBuildKey(typeToBuild, key.Name));
// An Override is created so that in the next BuildUp the already
// built object gets used instead of doing the BuildUp again and
// entering an infinite loop
_context.AddResolverOverrides(new DependencyOverride(key.Type, value));
}
_context.Existing = value;
_context.BuildComplete = true;
}
private IEnumerable<Type> GetDecoratorTypes(Type _type)
{
var typeList = m_typeStacks.GetValueOrDefault(_type) ?? new List<DecoratorRegistration>(0);
if (!_type.IsGenericType)
return typeList.Select(_reg => _reg.Type);
// If the type is a generic type, we need to get all open generic registrations
// alongside the closed ones
var openGenericList = m_typeStacks
.GetValueOrDefault(_type.GetGenericTypeDefinition()) ??
new List<DecoratorRegistration>(0);
// The final result is an ordered concatenation of the closed and open registrations
// that should be used for the type
return typeList
.Concat(openGenericList)
.OrderBy(_registration => _registration.Order)
.Select(_reg => _reg.Type);
}
}
这就是使用 DecoratorRegistration 模型的地方。它只是一对表示注册顺序的 type/int。我创建它是为了能够正确混合打开和关闭的通用注册:
internal struct DecoratorRegistration
{
public int Order { get; set; }
public Type Type { get; set; }
}
这在很大程度上创造了奇迹。当我有一个实现两个接口的类时,问题就开始了,一个是装饰的,一个不是。
这是我正在尝试进行的当前测试用例:
private interface IAny<T> {}
private interface IAnotherInterface {}
private class Base<T> : IAnotherInterface, IAny<T> {}
private class Decorator1<T> : IAny<T>
{
internal readonly IAny<T> Decorated;
public Decorator1(IAny<T> _decorated)
{
Decorated = _decorated;
}
}
[TestMethod]
public void DecoratorExtensionDoesNotInterfereWithNormalRegistrations()
{
// Arrange
var container = new UnityContainer()
.AddNewExtension<DecoratorExtension>()
.RegisterType<Base<string>>(new ContainerControlledLifetimeManager())
.RegisterType<IAny<string>, Decorator1<string>>()
.RegisterType<IAny<string>, Base<string>>()
.RegisterType<IAnotherInterface, Base<string>>();
// Act
var decorated = container.Resolve<IAny<string>>();
var normal = container.Resolve<IAnotherInterface>();
var anotherDecorated = container.Resolve<IAny<string>>();
var anotherNormal = container.Resolve<IAnotherInterface>();
// Assert
Assert.IsInstanceOfType(normal, typeof (IAnotherInterface));
Assert.IsInstanceOfType(decorated, typeof (Decorator1<string>));
Assert.AreSame(normal, anotherNormal);
Assert.AreSame(decorated, anotherDecorated);
}
这个测试应该让我的意图清楚。我想要单例类,但是对 Resolve 的第一次调用,IAnotherInterface
或者IAny<string>
导致每个后续调用都返回相同的东西。因此,我得到一个例外:
System.InvalidCastException: Unable to cast object of type 'Decorator1`1[System.String]' to type 'IAnotherInterface'.
在这条线上:
var normal = container.Resolve<IAnotherInterface>();
我不确定在这里做什么。我不得不在我们的项目中暂时禁用单例,以便它可以按预期工作。我想要的是该Base<string>
实例是一个单例,但是当我请求它时IAny<string>
,它会创建一个新的实例,其中 SAME 基被装饰。
这仍然使用.Net 4.0,所以我在这里坚持使用Unity 2.1(不过在这种情况下应该没关系)。