You should centralize calls to an event. That is, create a virtual method in your component that calls the application's event handler (if it assigns one) and provides any default handling. 

Putting all the event calls in one place ensures that someone deriving a new component from yours can customize event handling by overriding a single method, rather than searching through your code for places where you call the event. 

There are two other considerations when calling the event:

• Empty handlers must be valid.
• Users can override default handling.