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IErrorHandler.HandleError Method

Enables error-related processing and returns a value that indicates whether the dispatcher aborts the session and the instance context in certain cases.

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

bool HandleError(
	Exception error
)

Parameters

error
Type: System.Exception

The exception thrown during processing.

Return Value

Type: System.Boolean
true if Windows Communication Foundation (WCF) should not abort the session (if there is one) and instance context if the instance context is not Single; otherwise, false. The default is false.

Use the HandleError method to implement error-related behaviors such as error logging, system notifications, shutting down the application, and so on, and return a value that specifies whether the exception has been handled appropriately.

NoteNote

Because the HandleError method can be called from many different places there are no guarantees made about which thread the method is called on. Do not depend on HandleError method being called on the operation thread.

All IErrorHandler implementations are called. By default (when the return value is false), if there is an exception, the dispatcher aborts any session and aborts the InstanceContext if the InstanceContextMode is anything other than Single.  The exception is then considered unhandled and any state is considered corrupt.

Return true from HandleError to prevent this default behavior. If any error handler returns true it instructs WCF that it is safe to continue using state associated with the failed request.

If no error handler returns true from the HandleError method the exception is considered unhandled and the default response applies, potentially resulting in an aborted System.ServiceModel.InstanceContext and channel when communicating on a session channel or the ServiceBehaviorAttribute.InstanceContextMode property is not set to InstanceContextMode.Single.

The error parameter is never null and contains the exception object that was thrown.

The following code example demonstrates a service that implements IErrorHandler that returns only FaultException<TDetail> of type GreetingFault when a service method throws a managed exception.

#region IErrorHandler Members
public bool HandleError(Exception error)
{
  Console.WriteLine("HandleError called.");
  // Returning true indicates you performed your behavior. 
  return true;
}

// This is a trivial implementation that converts Exception to FaultException<GreetingFault>. 
public void ProvideFault(
  Exception error,
  MessageVersion ver,
  ref Message msg
)
{
  Console.WriteLine("ProvideFault called. Converting Exception to GreetingFault....");
  FaultException<GreetingFault> fe 
    = new FaultException<GreetingFault>(new GreetingFault(error.Message));
  MessageFault fault = fe.CreateMessageFault();
  msg = Message.CreateMessage(
    ver, 
    fault, 
    "http://microsoft.wcf.documentation/ISampleService/SampleMethodGreetingFaultFault"
  );
}
#endregion

The following code example shows how to use a service behavior to add the IErrorHandler implementation to the ErrorHandlers property.

// This behavior modifies no binding parameters.
#region IServiceBehavior Members
public void AddBindingParameters(
  ServiceDescription description, 
  ServiceHostBase serviceHostBase, 
  System.Collections.ObjectModel.Collection<ServiceEndpoint> endpoints, 
  System.ServiceModel.Channels.BindingParameterCollection parameters
)
{
  return;
}

// This behavior is an IErrorHandler implementation and  
// must be applied to each ChannelDispatcher. 
public void ApplyDispatchBehavior(ServiceDescription description, ServiceHostBase serviceHostBase)
{
  Console.WriteLine("The EnforceGreetingFaultBehavior has been applied.");
  foreach(ChannelDispatcher chanDisp in serviceHostBase.ChannelDispatchers)
  {
    chanDisp.ErrorHandlers.Add(this);      
  }
}

// This behavior requires that the contract have a SOAP fault with a detail type of GreetingFault. 
public void Validate(ServiceDescription description, ServiceHostBase serviceHostBase)
{
  Console.WriteLine("Validate is called.");
  foreach (ServiceEndpoint se in description.Endpoints)
  {
    // Must not examine any metadata endpoint. 
    if (se.Contract.Name.Equals("IMetadataExchange")
      && se.Contract.Namespace.Equals("http://schemas.microsoft.com/2006/04/mex"))
      continue;
    foreach (OperationDescription opDesc in se.Contract.Operations)
    {
      if (opDesc.Faults.Count == 0)
        throw new InvalidOperationException(String.Format(
          "EnforceGreetingFaultBehavior requires a "  
          + "FaultContractAttribute(typeof(GreetingFault)) in each operation contract.  "
          + "The \"{0}\" operation contains no FaultContractAttribute.",
          opDesc.Name)
        );
      bool gfExists = false;
      foreach (FaultDescription fault in opDesc.Faults)
      {
        if (fault.DetailType.Equals(typeof(GreetingFault)))
        {
          gfExists = true;
          continue;
        }
      }
      if (gfExists == false)
      {
        throw new InvalidOperationException(
"EnforceGreetingFaultBehavior requires a FaultContractAttribute(typeof(GreetingFault)) in an operation contract."
        );
      }
    }
  }
}
#endregion

The following code example shows how to configure the service to load the service behavior using an application configuration file. For more details about how to expose a service behavior in a configuration file, see IServiceBehavior.

<configuration>
  <system.serviceModel>
    <services>
      <service 
        name="Microsoft.WCF.Documentation.SampleService"
        behaviorConfiguration="metaAndErrors">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8080/SampleService"/>
          </baseAddresses>
        </host>
        <endpoint
          address=""
          binding="wsHttpBinding"
          contract="Microsoft.WCF.Documentation.ISampleService"
         />
        <endpoint
          address="mex"
          binding="mexHttpBinding"
          contract="IMetadataExchange"
         />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="metaAndErrors">
          <serviceDebug includeExceptionDetailInFaults="true"/>
          <serviceMetadata httpGetEnabled="true"/>
          <enforceGreetingFaults />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <extensions>
      <behaviorExtensions>
        <add 
          name="enforceGreetingFaults" 
          type="Microsoft.WCF.Documentation.EnforceGreetingFaultBehavior, HostApplication, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"
        />
      </behaviorExtensions>
    </extensions>
  </system.serviceModel>
</configuration>
<configuration>
  <system.serviceModel>
    <services>
      <service 
        name="Microsoft.WCF.Documentation.SampleService"
        behaviorConfiguration="metaAndErrors">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8080/SampleService"/>
          </baseAddresses>
        </host>
        <endpoint
          address=""
          binding="wsHttpBinding"
          contract="Microsoft.WCF.Documentation.ISampleService"
         />
        <endpoint
          address="mex"
          binding="mexHttpBinding"
          contract="IMetadataExchange"
         />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="metaAndErrors">
          <serviceDebug includeExceptionDetailInFaults="true"/>
          <serviceMetadata httpGetEnabled="true"/>
          <enforceGreetingFaults />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <extensions>
      <behaviorExtensions>
        <add 
          name="enforceGreetingFaults" 
          type="Microsoft.WCF.Documentation.EnforceGreetingFaultBehavior, HostApplication, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null"
        />
      </behaviorExtensions>
    </extensions>
  </system.serviceModel>
</configuration>

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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