typedef TScrollEvent TScrollEvent;
TScrollEvent is the type of an OnScroll event handler.
TScrollEvent defines the type of method procedure that you must define in order to implement the OnScroll event of a visual component such as TScrollBar.
The OnScroll event occurs when the user scrolls a scroll bar with the mouse or keyboard.
Sender is a reference to the component invoking the OnScroll event.
ScrollCode defines the user scroll action that was performed.
ScrollPos provides the new scroll position.