Event Handlers Are Optional
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When creating events, remember that developers using your components may not attach handlers to them. This means that your component should not fail or generate errors simply because there is no handler attached to a particular event. (The mechanics of calling handlers and dealing with events that have no attached handler are explained in Calling the Event.)
Events happen almost constantly in a GUI application. Just moving the mouse pointer across a visual component sends numerous mouse-move messages, which the component translates into OnMouseMove events. In most cases, developers do not want to handle the mouse-move events, and this should not cause a problem. So the components you create should not require handlers for their events.
Moreover, application developers can write any code they want in an event handler. The components in the class library have events written in such a way as to minimize the chance of an event handler generating errors. Obviously, you cannot protect against logic errors in application code, but you can ensure that data structures are initialized before calling events so that application developers do not try to access invalid data.