IInstanceProvider Interface

 
System_CAPS_noteNote

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Declares methods that provide a service object or recycle a service object for a Windows Communication Foundation (WCF) service.

Namespace:   System.ServiceModel.Dispatcher
Assembly:  System.ServiceModel (in System.ServiceModel.dll)

Public Interface IInstanceProvider

NameDescription
System_CAPS_pubmethodGetInstance(InstanceContext)

Returns a service object given the specified InstanceContext object.

System_CAPS_pubmethodGetInstance(InstanceContext, Message)

Returns a service object given the specified InstanceContext object.

System_CAPS_pubmethodReleaseInstance(InstanceContext, Object)

Called when an InstanceContext object recycles a service object.

Implement the IInstanceProvider interface to control the creation and recycling of service objects when one is requested or disposed by an InstanceContext object.

Once the IInstanceProvider interface is implemented, you must assign your custom instance provider object to the InstanceProvider property using either an endpoint behavior (a IEndpointBehavior object) or a contract behavior (a IContractBehavior object).

If the insertion mechanism is an endpoint behavior you can also implement a BehaviorExtensionElement object that can insert your custom behavior using a configuration file. If the insertion mechanism is a contract behavior, you can insert the behavior programmatically prior to the opening of the service host or you can implement a custom attribute. (For an example of the contract behavior approach, see the Example section.)

IInstanceProvider has two methods, GetInstance and ReleaseInstance. These methods are typically implemented to create service objects using a non-default constructor or to initialize or dispose of some state related to the lifetime of the object. Service object pooling is one example of custom IInstanceProvider functionality.

Typically, the InstanceContext invokes the GetInstance when the InstanceContext is first created and invokes the ReleaseInstance method when the InstanceContext is closed.

There are two ways to cause an InstanceContext object to release a service object before the InstanceContext is closed. The first method is to set the ReleaseInstanceMode to AfterCall or BeforeAndAfterCall. The second method is to call the ReleaseServiceInstance method. If this is done, the InstanceContext calls the ReleaseInstance method on the dispatcher's instance provider. If a new message arrives after the instance has been released, WCF creates a new instance using the GetInstance method.

System_CAPS_noteNote

If the InstanceContextMode of the service is Single, the system does not call the GetInstance or ReleaseInstance methods even when the user did not provide a well-known service object unless the user directly calls ReleaseServiceInstance and then calls GetServiceInstance.

The following code example shows how to implement IInstanceProvider that provides "singleton" behavior; it always returns the same service instance and does not recycle it.

 Public Class ObjectProviderBehavior
  Implements IInstanceProvider

Private message As String
Private service As SampleService = Nothing

Public Sub New(ByVal msg As String)
  Console.WriteLine("The non-default constructor has been called.")
  Me.message = msg
  Me.service = New SampleService("Singleton sample service.")
End Sub

#Region "IInstanceProvider Members"

Public Function GetInstance(ByVal instanceContext As InstanceContext, ByVal message As System.ServiceModel.Channels.Message) As Object Implements IInstanceProvider.GetInstance
  Console.WriteLine("GetInstance is called:")
  Return Me.service
End Function

Public Function GetInstance(ByVal instanceContext As InstanceContext) As Object Implements IInstanceProvider.GetInstance
  Console.WriteLine("GetInstance is called:")
  Return Me.service
End Function

Public Sub ReleaseInstance(ByVal instanceContext As InstanceContext, ByVal instance As Object) Implements IInstanceProvider.ReleaseInstance
  Console.WriteLine("ReleaseInstance is called. The SingletonBehaviorAttribute never releases.")
End Sub

#End Region
 End Class

The following code example shows how to implement a custom attribute that implements IContractBehavior to insert the custom service instance provider. It also implements IContractBehaviorAttribute, which binds its use to a specific contract.

 Public Class SingletonBehaviorAttribute
  Inherits Attribute
  Implements IContractBehaviorAttribute, IContractBehavior

#Region "IContractBehaviorAttribute Members"

Public ReadOnly Property TargetContract() As Type Implements IContractBehaviorAttribute.TargetContract
  Get
	  Return GetType(ISampleService)
  End Get
End Property

#End Region

#Region "IContractBehavior Members"

Public Sub AddBindingParameters(ByVal description As ContractDescription, ByVal endpoint As ServiceEndpoint, ByVal parameters As System.ServiceModel.Channels.BindingParameterCollection) Implements IContractBehavior.AddBindingParameters
  Return
End Sub

Public Sub ApplyClientBehavior(ByVal description As ContractDescription, ByVal endpoint As ServiceEndpoint, ByVal clientRuntime As ClientRuntime) Implements IContractBehavior.ApplyClientBehavior
  Return
End Sub

Public Sub ApplyDispatchBehavior(ByVal description As ContractDescription, ByVal endpoint As ServiceEndpoint, ByVal dispatch As DispatchRuntime) Implements IContractBehavior.ApplyDispatchBehavior
  dispatch.InstanceProvider = New ObjectProviderBehavior("Custom ObjectProviderBehavior constructor.")
End Sub

Public Sub Validate(ByVal description As ContractDescription, ByVal endpoint As ServiceEndpoint) Implements IContractBehavior.Validate
  Return
End Sub

#End Region
 End Class

.NET Framework
Available since 3.0
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