When you delete a component from a form using the Form Designer, the Code editor removes the component from the form's type declaration. It does not, however, delete any associated methods from the unit file, since these methods may still be called by other components on the form. You can manually delete a method—such as an event handler—but if you do so, be sure to delete both the method's forward declaration (in the unit's interface section) and its implementation (in the implementation section). Otherwise you'll get a compiler error when you build your project.