[Autofac]服务类型、 名称和键

 TypedNamedAndKeyedServices  

Many implementations of the same service can be differentiated using names and keys.

同一服务的多个实现可以使用名称和键来区分。 
Autofac2

Updated Aug 17, 2010 by [e-mail]

Autofac provides three typical ways to identify services.

Autofac 提供了3种典型的方式来标识服务。

By Type 按类型

The default method of describing a service is as a type.

描述服务的默认方法是把他当作一个特定的类型。

builder.Register<OnlineState>().As<IDeviceState>();

This example associates the IDeviceState typed service with the OnlineState component. Instances of the component can be retrieved using the service type with the Resolve() method:

这个例子把IDeviceState类型的服务和OnlineState组件联系起来。组件实例可以通过Resolve() 方法并使用服务类型来获得。

var r = container.Resolve<IDeviceState>();

Typed services also work with Autowiring.

类型服务在自动装备中也同样有效。

By Name 按名称

Services can be further identified using a service name. Using this technique, the Named() registration method replaces As().

服务可以进一步使用名称来标识。这个技术通过使用Named()注册方法来替代As()方法。

builder.Register<OnlineState>().Named<IDeviceState>("online");

To retrieve a named service, the ResolveNamed() method is used:

要获取一个命名服务的实例，可以使用ResolveNamed() 方法。

var r = container.ResolveNamed<IDeviceState>("online");

In versions of Autofac prior to 2.3, ResolveNamed() is simply an overload of Resolve().

在Autofac之前的2.3版本中，ResolveNamed() 方法只是Resolve().方法的简单重载。

Named services are simply keyed services that use a string as a key, and so the techniques described in the next section apply equally to named services.

命名服务使用字符串来当作键值，它其实是键值服务的简单版本。所以下节描述的技术也同样适用于命名服务。

By Key 按键值

Using strings as component names is convenient in some cases, but in others we may wish to use keys of other types. Keyed services provide this ability.

在某些情况下，使用字符串作为组件的名称是很方便的。但在另外一些情况中，我们可能希望使用其他类型来作为键值。键值服务提供这种功能。

For example, an enum may describe the different device states in our example:

例如使用枚举来描述设备的不同状态。

public enum DeviceState { Online, Offline }

Each enum value corresponds to an implementation of the service:

每个枚举值和一个服务实现相对应：

public class OnlineState : IDeviceState { }

The enum values can then be registered as keys for the implementations as shown below.

可以向下面这样使用枚举值注册为服务的实现。

var builder = new ContainerBuilder();builder.RegisterType<OnlineState>().Keyed<IDeviceState>(DeviceState.Online);builder.RegisterType<OfflineState>().Keyed<IDeviceState>(DeviceState.Offline);// Register other components here

Resolving Explicitly 显示检索

The implementation can be resolved explicitly with ResolveKeyed():

服务实例可以使用 ResolveKeyed()来显示取得：

var r = container.ResolveKeyed<IDeviceState>(DeviceState.Online);

This does however result in using the container as a Service Locator, which is discouraged. As an alternative to this pattern, the IIndex type is provided.

但是，这会导致把容器当作服务定位器来使用，而这是不提倡的。Autofac提供了IIndex类型来作为这一模式的替代方案。

In versions of Autofac prior to 2.3, ResolveKeyed() is simply an overload of Resolve().

在Autofac之前的2.3版本中，ResolveKeyed() 方法只是Resolve().方法的简单重载。

Resolving with an Index 使用索引检索

Autofac.Features.Indexed.IIndex<K,V> is a relationship type that Autofac implements automatically. Components that need to choose between service implementations based on a key can do so by taking a constructor parameter of type IIndex<K,V>.

Autofac.Features.Indexed.IIndex<K,V>是Autofac自动实现的一个关系类型。通过键值选取的组件实现，也可以通过使用IIndex<K,V>作为构造函数参数来取得。

public class Modem : IHardwareDevice{    IIndex<DeviceState, IDeviceState> _states;    IDeviceState _currentState;    public Modem(IIndex<DeviceState, IDeviceState> states)    {         _states = states;         SwitchOn();    }    void SwitchOn()    {         _currentState = _states[DeviceState.Online];    }}

In the SwitchOn() method, the index is used to find the implementation of IDeviceState that was registered with the DeviceState.Online key.

在SwitchOn() 方法中，使用索引来取得通过DeviceState.Online键值注册的IDeviceState的实现。