Making Events Visible
Go Up to Implementing the Standard Events
The declarations of the standard events in TControl and TWinControl are protected, as are the methods that correspond to them. If you are inheriting from one of these abstract classes and want to make their events accessible at run time or design time, you need to redeclare the events as either public or published.
Redeclaring a property without specifying its implementation keeps the same implementation methods, but changes the protection level. You can, therefore, take an event that is defined in TControl but not made visible, and surface it by declaring it as public or published.