Why WCF always gives CommunicationObjectFaultedException?

I have been frustrated regarding WCF - it always seemed to give the same obscure exception:

CommunicationObjectFaultedException - The communication object cannot be used because it is in the Faulted state

Finally I found out why.

Actually WCF usually throws clear exceptions. You just have to use it right.

I have been using WCF proxys with a C# using statement. And here the trouble lies.

What the C# using statement does is this: it wraps up the using block in a try clause, and in the finally clause it disposes the object given in the using clause. In other words, it ensures the object gets disposed even if an exception occured inside the block.

This is very good for working with files, etc. But with WCF it is a problem. Why? because the WCF proxy's Dispose method actually calls the proxy's Close method. But this Close method has a catch: if the proxy is in a Faulted state, Close() throws the infamous exception CommunicationObjectFaultedException.

So what happens is this: you call a method on a service and get an exception. This puts the proxy in a faulted state. Then the using block calls Dispose on the proxy, and the CommunicationObjectFaultedException is thrown.

A WCF proxy in a faulted state still holds some resources. And to dispose of them, you need to call the proxy's Abort method. This method does not throw an exception if the proxy is in a faulted state.

So the recommended pattern to use a WCF proxy is this:

// Create the proxy object here

try

{

     proxy.MyMethod();

}

finally
{
    if (proxy != null)
    {
        if (proxy.State == System.ServiceModel.CommunicationState.Faulted)
        {
            proxy.Abort();
        }
        else
        {
            proxy.Close();
        }
    }
}

The writer is a .Net team leader at Niloosoft Hunter HRMS