Originally Posted by
alone882
The :ListBox1KeyPress method takes a pointer to a TObject called Sender. Mostly, every event handler, in c++, will have at least a Sender parameter. When the button is clicked, the event handler (:ListBox1KeyPress) for the KeyPress event is called.
The parameter "Sender" references the control that was used to call the method. If you press on the ListBox1 control, causing the ListBox1KeyPress method to be called, a reference or pointer to the ListBox1 object is passed to ListBox1KeyPress in the parameter called Sender