Question

Let’s say I have a “Processor” interface exposing an event – OnProcess. Usually the implementors do the processing. Thus I can safely subscribe on this event and be sure it will be fired. But one processor doesn’t do processing – thus I want to prevent subscribers to subscibe on it. Can I do that? In other words in the code below I want the last line to throw an exception:

var emptyProcessor = new EmptyProcessor();
emptyProcessor.OnProcess += event_handler; // This line should throw an exception.

Answer 1

class EmptyProcessor : IProcessor {

    [Obsolete("EmptyProcessor.OnProcess should not be directly accessed", true)]
    public event EventHandler OnProcess { 
        add { throw new NotImplementedException(" :( "); }
        remove { }
    }
}

In this situation, the true parameter on Obsolete causes a compile-time exception. so:

EmptyProcessor processor1 = new EmptyProcessor();
IProcessor processor2 = new EmptyProcessor();

processor1.OnProcess += handler;  // <-- compile-time error
processor2.OnProcess += handler;  // <-- run-time error