Silverlight Exception Handling Application From WCF in VB.NET

This article explains about handling the exception in Silverlight application from WCF.
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This article explains about handling the exception in Silverlight application from WCF. I have created the sample Silverlight application, which uses the WCF service for process the data. While testing the application I came to know that exception message thrown from WCF cannot be received at the client side(Silverlight application) even after using the FaultException. I was always getting System.ServiceModel.CommunicationException: The remote server returned an error: NotFound.

Later I came to know that WCF throws the HTTP 500 series Fault message but Silverlight can handle only 200 series. So we need to convert the 500 series to 200 error message for Silverlight. Here is the sample application for exception handling between WCF and Silverlight.

Step 1: 

We can customize the Endpoint behavior of the WCF service by inheriting the BehaviorExtensionElement and implementing the IEndpointBehavior. Actual code for converting the 500 error serice to 200 serivce in BeforeSendReply method.

Create a ClassLibrary project and name it as "Silverlight_WCF_FaultBehavior" and name the class as "SilverlightFaultBehavior". Copy and paste the following code inside the SilverlightFaultBehavior class.

Imports System.ServiceModel.Configuration
Imports System.ServiceModel.Description
Imports System.ServiceModel.Dispatcher
Imports System.ServiceModel.Channels
Imports System.ServiceModel

    Public Class SilverlightFaultBehavior
        Inherits BehaviorExtensionElement
        Implements IEndpointBehavior
        Public Overrides ReadOnly Property BehaviorType() As System.Type
                Return GetType(SilverlightFaultBehavior)
            End Get
        End Property
        Protected Overrides Function CreateBehavior() As Object
            Return New SilverlightFaultBehavior
        End Function
        Public Sub AddBindingParameters(ByVal endpoint AsSystem.ServiceModel.Description.ServiceEndpoint, ByVal bindingParameters AsSystem.ServiceModel.Channels.BindingParameterCollection) ImplementsSystem.ServiceModel.Description.IEndpointBehavior.AddBindingParameters
        End Sub
        Public Sub ApplyClientBehavior(ByVal endpoint AsSystem.ServiceModel.Description.ServiceEndpoint, ByVal clientRuntime AsSystem.ServiceModel.Dispatcher.ClientRuntime) ImplementsSystem.ServiceModel.Description.IEndpointBehavior.ApplyClientBehavior
        End Sub
        Public Sub ApplyDispatchBehavior(ByVal endpoint AsSystem.ServiceModel.Description.ServiceEndpoint, ByVal endpointDispatcher AsSystem.ServiceModel.Dispatcher.EndpointDispatcher) ImplementsSystem.ServiceModel.Description.IEndpointBehavior.ApplyDispatchBehavior
            Dim inspector As New SilverlightFaultMessageInspector()
        End Sub
        Public Sub Validate(ByVal endpoint As System.ServiceModel.Description.ServiceEndpoint)Implementsystem.ServiceModel.Description.IEndpointBehavior.Validate
        End Sub
        Public Class SilverlightFaultMessageInspector
            Implements IDispatchMessageInspector
            Public Function AfterReceiveRequest(ByRef request AsSystem.ServiceModel.Channels.Message, ByVal channel As System.ServiceModel.IClientChannel,ByVal instanceContext As System.ServiceModel.InstanceContext) As Object ImplementsSystem.ServiceModel.Dispatcher.IDispatchMessageInspector.AfterReceiveRequest
                ' Do nothing to the incoming message.
                Return Nothing
            End Function
            Public Sub BeforeSendReply(ByRef reply As System.ServiceModel.Channels.Message, ByValcorrelationState As ObjectImplementsSystem.ServiceModel.Dispatcher.IDispatchMessageInspector.BeforeSendReply
                If reply.IsFault Then
                    Dim [property] As New HttpResponseMessageProperty() 
                    ' Here the response code is changed to 200.
                    [property].StatusCode = System.Net.HttpStatusCode.OK
                    reply.Properties(HttpResponseMessageProperty.Name) = [property]
                End If
            End Sub
        End Class
    End Class

Note: Highlighted code shows the conversion for 500 series to 200 series error code.

Step 2:

Build the project

Step 3: 

Create a new WCF service with Interface and implementation class as follows


<ServiceContract()> _
Public Interface IService
    <OperationContract()> _
    Function Add(ByVal num1 As IntegerByVal num2 As IntegerAs Integer
    <OperationContract()> _
    Function Subtract(ByVal num1 As IntegerByVal num2 As IntegerAs Integer  
End Interface


Public Class Service
    Implements IService
    Public Sub New()
    End Sub
    Public Function Add(ByVal num1 As IntegerByVal num2 As IntegerAs Integer ImplementsIService.Add
        Throw New FaultException("Error thrown by user for Add operation")
        'Return num1 + num2
    End Function
    Public Function Subtract(ByVal num1 As IntegerByVal num2 As IntegerAs Integer ImplementsIService.Subtract
        Return num1 - num2
    End Function
End Class

Step 4:
Add the Silverlight_WCF_FaultBehavior project dll as reference to WCF Service

Step 5:

In WCF we can extend the binding and behavior by using <extention> tag. In our case also we are extending the custom endpoint behavior as shown below. In the <behaviorExtensions> tag we need specify the fully qualified name of the custom behavior assembly.

Modify the Web.config file as shown below

      <service name="Service" behaviorConfiguration="ServiceBehavior">
        <!-- Service Endpoints -->
        <endpoint address="" binding="basicHttpBinding" contract="IService"behaviorConfiguration="SilverlightFaultBehavior">
              Upon deployment, the following identity element should be removed or replaced to reflect the
              identity under which the deployed service runs.  If removed, WCF will infer an appropriate identity
            <dns value="localhost"/>
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
        <behavior name="ServiceBehavior">
          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        <behavior name="SilverlightFaultBehavior">
        <add name="silverlightFaults"type="Silverlight_WCF_FaultBehavior.SilverlightFaultBehavior, Silverlight_WCF_FaultBehavior, Version=,
Culture=neutral, PublicKeyToken=null"/>

Step 6:

Create the any sample silverlight application as "Silverlight_WCF_Exception" and add this WCF service as Service Reference.

url: http://localhost/MathService/Service.svc 

Step 7: 

Add a button to the MainPage.xaml and call the WCF method as shown below

Private Sub Button_Click(ByVal sender As System.Object, ByVal e AsSystem.Windows.RoutedEventArgs)
        Dim proxy As New ServiceProxy.ServiceClient
        AddHandler proxy.AddCompleted, AddressOf AddOperationCompleted
        proxy.AddAsync(5, 6)
End Sub
Private Sub AddOperationCompleted(ByVal sender As ObjectByVal e AsServiceProxy.AddCompletedEventArgs)
        If e.Error IsNot Nothing Then
        End If
End Sub

Step 8:

Output will look like this


This article explains about handling the exception in Silverlight application from WCF. I will get back to you guy's with another article.


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