Programming WCF Services, 3rd Edition

The Trace Interceptors

The first example I’ll show of using the generic interceptors framework is for tracing and logging. Example E-5 shows a simple example of implementing a generic service-side interceptor called ParameterTracerInvoker.

Example E-5. The ParameterTracerInvoker

class ParameterTracerInvoker : GenericInvoker
{
   public ParameterTracerInvoker(IOperationInvoker oldInvoker) : base(oldInvoker)
   {}

   protected override void PreInvoke(object instance,object[] inputs)
   {
      Trace.WriteLine("Input Parameters: ");

      foreach(object argument in inputs)
      {
         Trace.WriteLine(argument.ToString());
      }
   }
   protected override void PostInvoke(object instance,object returnedValue,
                                      object[] outputs,Exception exception)
   {

      foreach(object output in outputs)
      {
         Trace.WriteLine("Output Parameters: ");
         Trace.WriteLine(output.ToString());
      }

      Trace.WriteLine("Returned: " + returnedValue ?? String.Empty);
   }
}

ParameterTracerInvoker derives from GenericInvoker. Its constructor accepts the old invoker and passes it to the constructor of GenericInvoker. The implementations of PreInvoke() and PostInvoke() trace to the Output window in Visual Studio the values of the input and output parameters, respectively. You can install the ParameterTracerInvoker on service operations by defining the OperationParameterTracerAttribute:

public class OperationParameterTracerAttribute : OperationInterceptorBehaviorAttribute { protected override GenericInvoker CreateInvoker(IOperationInvoker oldInvoker) { return new ParameterTracerInvoker(oldInvoker); ...