Handling Exception in Silverlight application from WCF
Attachment:
Silverlight_WCF_Exception.zipThis 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 Beha 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 “S
ilverlight_WCF_FaultBehavior” and name the class as “SilverlightFaultBehavior”. Copy and paste the follwing code inside the SilverlightFaultBehavior class.
Imports System.ServiceModel.ConfigurationrviceModel.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
Get Return GetType(SilverlightFaultBehavior)
End Get End Property
Protected Overrides Function CreateBehavior() As Object
Return New SilverlightFaultBehavior End Function
Public Sub AddBindingParameters(ByVal endpoint As ServiceEndpoint,
ByVal bindingParameters As BindingParameterCollection)
Implements IEndpointBehavior.AddBindingParameters End Sub
Public Sub ApplyClientBehavior(ByVal endpoint As ServiceEndpoint,
ByVal clientRuntime As ClientRuntime)
Implements IEndpointBehavior.ApplyClientBehavior End Sub
Public Sub ApplyDispatchBehavior(ByVal endpoint As ServiceEndpoint,
ByVal endpointDispatcher As EndpointDispatcher) Implements IEndpointBehavior.ApplyDispatchBehavior Dim inspector As New SilverlightFaultMessageInspector() endpointDispatcher.DispatchRuntime.MessageInspectors.Add(inspector) End Sub Public Sub Validate(ByVal endpoint As ServiceEndpoint) Implements IEndpointBehavior.Validate End Sub Public Class SilverlightFaultMessageInspector Implements IDispatchMessageInspector Public Function AfterReceiveRequest(ByRef request As Message, ByVal channel As IClientChannel, ByVal instanceContext As InstanceContext) As Object Implements IDispatchMessageInspector.AfterReceiveRequest ' Do nothing to the incoming message. Return Nothing End Function Public Sub BeforeSendReply(ByRef reply As System.ServiceModel.Channels.Message, ByVal correlationState As Object) Implements 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 conver
sion for 500 serices to 200 series error code.
Step 2: Build the project
Step 3: Create a new WCF service with Interface and implementation class as follows
Interface
<ServiceContract()> _ Public Interface IService
<OperationContract()> _ Function Add(ByVal num1 As Integer,
ByVal num2 As Integer) As Integer <OperationContract()> _
Function Subtract(ByVal num1 As Integer, ByVal num2 As Integer) As Integer
End Interface
Implementation
Public Class Service Implements ISe
rvice Public Sub New() End Sub< Add the Silverlight_WCF_FaultBehavior project dll as reference to WCF Service
Public Function Add(ByVal num1 As Integer, ByVal num2 As Integer)
As Integer Implements IService.Add
Throw New FaultException("Error thrown by user for Add operation")
'Return num1 + num2 End Function
Public Function Subtract(ByVal num1 As Integer,
ByVal num2 As Integer) As Integer Implements IService.Subtract
Return num1 - num2 End Function End Class
Step 5:
Step 5: In WCF we can extend the bin ding 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 cutom behaviour assembly.
Modify the Web.config file as shown be llow
<system.serviceModel> <services>
<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 automatically.-->
<identity> <dns value="localhost"/>
</identity> </endpoint>
<endpoint address="mex" binding="mexHttpBinding"
contract="IMetadataExchange"/> </service>
</services> <behaviors> <serviceBehaviors>
<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> </serviceBehaviors>
<endpointBehaviors> <behavior name="SilverlightFaultBehavior">
<silverlightFaults/> </behavior>
</endpointBehaviors> </behaviorss=“BlueCode”>>
<extensions> <behaviorExtensions>
<add name="silverlightFaults"
type="Silverlight_WCF_FaultBehavior.SilverlightFaultBehavior,
Silverlight_WCF_FaultBehavior, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=null"/> </behaviorExtensions>
</extensionss=“BlueCode”>> </system.serviceModel>
Step 6: Create the any sample silverlight application as “Silverlight_WCF_Exception” and add this WCF service as Service Reference.
url: http://localhost/MathService/S ervice.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 As System.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 Object, ByVal e As ServiceProxy.AddCompletedEventArgs) If e.Error IsNot Nothing Then MessageBox.Show(e.Error.Message) Else MessageBox.Show(e.Result) End If End Sub Step 8: Output will look like this
Step 8: Output will look like this
