Events Are Method Pointers
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Delphi uses method pointers to implement events. A method pointer is a special pointer type that points to a specific method in a specific class instance. As a component writer, you can treat the method pointer as a placeholder: When your code detects that an event occurs, you call the method (if any) specified by the user for that event.
Method pointers work just like any other procedural type, but they maintain a hidden pointer to a class instance. When the application developer assigns a handler to a component's event, the assignment is not just to a method with a particular name, but rather to a method of a specific class instance. That instance is usually the form that contains the component, but it need not be.