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copied!<p>I've written this up in a fair amount of detail in <a href="http://pobox.com/~skeet/csharp/events.html" rel="noreferrer">an article</a>, but here's the summary, assuming you're reasonably happy with <a href="http://msdn.microsoft.com/en-us/library/ms173171.aspx" rel="noreferrer">delegates</a> themselves:</p> <ul> <li>An event is just an "add" method and a "remove" method, in the same way that a property is really just a "get" method and a "set" method. (In fact, the CLI allows a "raise/fire" method as well, but C# never generates this.) Metadata describes the event with references to the methods.</li> <li>When you declare a <em><a href="http://msdn.microsoft.com/en-us/library/aa664455.aspx" rel="noreferrer">field-like event</a></em> (like your ElementAddedEvent) the compiler generates the methods <em>and a private field</em> (of the same type as the delegate). Within the class, when you refer to ElementAddedEvent you're referring to the field. Outside the class, you're referring to the field.</li> <li>When anyone subscribes to an event (with the += operator) that calls the add method. When they unsubscribe (with the -= operator) that calls the remove.</li> <li><p>For field-like events, there's some synchronization but otherwise the add/remove just call Delegate.<a href="http://msdn.microsoft.com/en-us/library/system.delegate.combine.aspx" rel="noreferrer">Combine</a>/<a href="http://msdn.microsoft.com/en-us/library/system.delegate.remove.aspx" rel="noreferrer">Remove</a> to change the value of the auto-generated field. Both of these operations assign to the backing field - remember that delegates are immutable. In other words, the autogenerated code is very much like this:</p> <pre><code>// Backing field // The underscores just make it simpler to see what's going on here. // In the rest of your source code for this class, if you refer to // ElementAddedEvent, you're really referring to this field. private EventHandler<EventArgs> __ElementAddedEvent; // Actual event public EventHandler<EventArgs> ElementAddedEvent { add { lock(this) { // Equivalent to __ElementAddedEvent += value; __ElementAddedEvent = Delegate.Combine(__ElementAddedEvent, value); } } remove { lock(this) { // Equivalent to __ElementAddedEvent -= value; __ElementAddedEvent = Delegate.Remove(__ElementAddedEvent, value); } } } </code></pre></li> <li><p>The initial value of the generated field in your case is <code>null</code> - and it will always become <code>null</code> again if all subscribers are removed, as that is the behaviour of Delegate.Remove.</p></li> <li><p>If you want a "no-op" handler to subscribe to your event, so as to avoid the nullity check, you can do:</p> <pre><code>public EventHandler<EventArgs> ElementAddedEvent = delegate {}; </code></pre> <p>The <code>delegate {}</code> is just an anonymous method which doesn't care about its parameters and does nothing.</p></li> </ul> <p>If there's anything that's still unclear, please ask and I'll try to help!</p>

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