具有无参数构造函数的 WCF 自定义 ServiceBehavior/InstanceProvider

Question

我们正在尝试对 WCF 服务使用依赖注入。该服务依赖于 Unity 容器。该容器用于查找实现 IJob 接口（基于方法调用中的 JobKey 参数）的适当类并调用其上的方法。

该服务托管在 MVC2 中。我从下面的片段中省略了尽可能多的不相关的内容。如果需要，可以提供完整的代码...

到目前为止我所做的：

基于此 MSDN 文章，我创建了一个自定义InstanceProvider，它应该实例化我的服务并向其传递一个容器。

然后，我创建了一个非常简单的 ServiceBehavior 来使用 InstanceProvider，最后创建了一个仅返回 ServiceBehavior 的 BehaviorExtension。

Public Class WCFDIInstanceProvider
    Implements IInstanceProvider

    Private ServiceType As Type

    Private Property _Container As IUnityContainer
    Private ReadOnly Property Container As IUnityContainer
        Get
            If _Container Is Nothing Then
                _Container = InitialiseContainer()
            End If
            Return _Container
        End Get
    End Property

    Public Sub New(ByVal ServiceType As Type)
        Me.ServiceType = ServiceType
    End Sub

    Private Function InitialiseContainer() As IUnityContainer
            'Code which scans assemblies and populates the container as appropriate
            'I'm confident this code works as I've tested it elsewhere
        Return Container
    End Function

    Public Function GetInstance(ByVal instanceContext As System.ServiceModel.InstanceContext) As Object Implements System.ServiceModel.Dispatcher.IInstanceProvider.GetInstance
        Return GetInstance(instanceContext, Nothing)
    End Function

    Public Function GetInstance(ByVal instanceContext As System.ServiceModel.InstanceContext, ByVal message As System.ServiceModel.Channels.Message) As Object Implements System.ServiceModel.Dispatcher.IInstanceProvider.GetInstance
        Return Container.Resolve(Me.ServiceType)
    End Function

End Class

还有 ServiceBehavior：

Public Class WCFDIServiceBehavior
Implements IServiceBehavior

    Public Sub ApplyDispatchBehavior(ByVal serviceDescription As System.ServiceModel.Description.ServiceDescription, ByVal serviceHostBase As System.ServiceModel.ServiceHostBase) Implements System.ServiceModel.Description.IServiceBehavior.ApplyDispatchBehavior
        For Each ChannelDispatcherBase As ChannelDispatcherBase In serviceHostBase.ChannelDispatchers
            Dim ChannelDispatcher As ChannelDispatcher = TryCast(ChannelDispatcherBase, ChannelDispatcher)
            If ChannelDispatcher IsNot Nothing Then
                For Each Dispatcher As EndpointDispatcher In ChannelDispatcher.Endpoints
                    Dispatcher.DispatchRuntime.InstanceProvider = New WCFDIInstanceProvider(serviceDescription.ServiceType)
                Next
            End If
        Next
    End Sub

最后，真正的行为扩展：

Public Class WCFDIBehaviorExtension
    Inherits BehaviorExtensionElement

    Public Overrides ReadOnly Property BehaviorType As System.Type
        Get
            Return GetType(WCFDIServiceBehavior)
        End Get
    End Property

    Protected Overrides Function CreateBehavior() As Object
        Return New WCFDIServiceBehavior
    End Function
End Class

WCF 配置工具似乎喜欢上述所有内容，并生成了以下配置 XML：

  <serviceHostingEnvironment multipleSiteBindingsEnabled="true"
                             aspNetCompatibilityEnabled="true">
      <serviceActivations>
          <add relativeAddress="WebJob.svc"
               service="MyApplication.WebJobService"
               factory="System.ServiceModel.Activation.ServiceHostFactory" />
      </serviceActivations>
  </serviceHostingEnvironment>
<standardEndpoints>
  <mexEndpoint>
    <standardEndpoint name="WebJobServiceMex" />
  </mexEndpoint>
</standardEndpoints>
<behaviors>
  <serviceBehaviors>
    <behavior name="WCFDIServiceBehavior">
      <serviceMetadata httpGetEnabled="true" />
      <serviceDebug includeExceptionDetailInFaults="true" />
      <WCFDIBehavior />
    </behavior>
  </serviceBehaviors>
</behaviors>
<services>
  <service name="WebJobService">
    <endpoint address="" binding="basicHttpBinding" bindingConfiguration="httpBinding"
      name="HTTPEndpoint" contract="MyApplication.JobService.Common.IWebJobService" />
    <endpoint binding="mexTcpBinding" bindingConfiguration="" name="mexEndpoint" />
  </service>
</services>

我得到的例外是：

System.ServiceModel.ServiceActivationException：服务 由于执行期间出现异常，无法激活“/MyAppDir/WebJob.svc” 汇编。异常消息为： 提供的服务类型 无法作为服务加载，因为它没有默认值 （无参数）构造函数。要解决该问题，请添加默认值 构造函数到该类型，或将该类型的实例传递给主机。

System.InvalidOperationException：提供的服务类型无法 被加载为服务，因为它没有默认值 （无参数）构造函数。要解决此问题，请添加默认值 构造函数到该类型，或将该类型的实例传递给主机。

WebHost failed to process a request.
 Sender Information: System.ServiceModel.ServiceHostingEnvironment+HostingManager/13982700
 Exception: System.ServiceModel.ServiceActivationException: The service '/MyAppDir/WebJob.svc' cannot be activated due to an exception during compilation.  The exception message is: The service type provided could not be loaded as a service because it does not have a default (parameter-less) constructor. To fix the problem, add a default constructor to the type, or pass an instance of the type to the host.. ---> System.InvalidOperationException: The service type provided could not be loaded as a service because it does not have a default (parameter-less) constructor. To fix the problem, add a default constructor to the type, or pass an instance of the type to the host.
   at System.ServiceModel.Dispatcher.InstanceBehavior..ctor(DispatchRuntime dispatch, ImmutableDispatchRuntime immutableRuntime)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime..ctor(DispatchRuntime dispatch)
   at System.ServiceModel.Dispatcher.DispatchRuntime.GetRuntimeCore()
   at System.ServiceModel.Dispatcher.ChannelDispatcher.OnOpened()
   at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)
   at System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout)
   [Blah]
 Process Name: w3wp
 Process ID: 2108

假设它没有应用我的自定义 ServiceBehavior ，这是有道理的 - 默认 ServiceBehavior 的 InstaceProvider 无法实例化该服务。

需要注意的一些事情：如果我向我的服务添加无参数构造函数，我不会收到异常（但当然，我也不会传递容器），所以我相当有信心我已经找到了来源问题

有人可以指出我做错了什么吗？

Answer 1

我猜问题出在 . Service 元素不包含behaviorConfiguration。此外，名称属性通常必须包含带有命名空间的类型名称。因此，在您的情况下，它应该是 MyApplication.WebJobService。

您还可以查看这些文章以获取替代实现 1，2。

Answer 2

我会把问题简单化。这与 Unity 无关，而是与实例化服务并将参数传递给构造函数有关。如果这是一个问题，请考虑使用属性注入。

我通常会让服务实例化 Unity 容器，这完全避免了这个问题。

“扫描程序集并填充容器的代码”听起来 MEF 可能比 Unity 更适合您。

编辑：我认为我建议属性注入是错误的。您根本不希望 Unity 创建服务实例。由于 UnityContainer.Resolve 是线程安全的（尽管配置需要锁定），您可以让服务创建并拥有容器的静态实例。容器实例将解决其他依赖关系。